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      • MA Rui, LIU Zhenlei, HE Pingping, YU Haifeng

        Available online:February 16, 2020  DOI: 10.7500/AEPS20190217002

        Abstract:In view of the fact that the traditional continuous power flow method is difficult to adapt to the AC/DC interconnected systems with access of large-scale wind power, this paper proposes a probabilistic continuous power flow calculation method for AC/DC systems with wind power. Based on the frequency regulation characteristics of conventional units and the voltage and frequency static characteristics of loads, the randomness of wind power output, the DC control mode and the frequency fluctuation deviation constraints are taken into account. Then this paper establishes the probabilistic continuous power flow equation of AC/DC systems with wind power considering the frequency modulation of power sources and load static characteristics of loads. Based on the Jacobian matrix of the modified equation, the load margin sensitivity index reflecting the frequency fluctuation, wind power output and control mode is derived. The power flow solution and load margin in multiple scenarios of N and N-1 states are obtained by combining Monte Carlo method and predictor-corrector method. The correctness and validity of the proposed method are verified by simulation results of the modified IEEE 39-bus system.

      • AN Haiqing, LI Zhendong, YUE Na, HUA Huichun, CHEN Junfa, ZHANG Guoliang

        Available online:February 16, 2020  DOI: 10.7500/AEPS20190613006

        Abstract:Flicker envelope tracking is the key to analyze voltage fluctuation and flicker. The square detection method recommended by IEC has a large error in the low frequency range of the voltage flicker. It is not suitable for the envelope tracking of voltage flicker caused by wind power integration. Aiming at the problem of voltage flicker caused by wind power integration, this paper proposes an envelope tracking method of voltage flicker based on sparse recovery algorithm. The extreme points of the voltage flicker signal are taken as the observation sequence, and a discrete cosine transform base with varying frequency is constructed according to the smoother variation characteristics of the flicker envelope at the low frequency band. Then the orthogonal matching pursuit algorithm is used to recover the optimal flicker envelope. By analyzing several types of voltage flicker signal with single-frequency flicker, multi-frequency flicker, fundamental frequency variation, harmonics and noise, the accuracy of the proposed algorithm to track the flicker envelope is demonstrated. Finally, the measured voltage fluctuation signals of the wind farm in Zhangbei flexible DC grid are analyzed, which verifies the feasibility and effectiveness of the proposed algorithm for tracking the voltage flicker envelope caused by wind power integration.

      • WANG Can, DU Chuan, XU Jiexiong

        Available online:February 16, 2020  DOI: 10.7500/AEPS20191021006

        Abstract:With the development of DC power transmission and distribution system, in order to better meet the requirements of DC system fault suppression and fault current removal, DC circuit breaker can be used to solve the problems of speed, stability and economy in DC fault removal. This paper discusses the development status of dc circuit breaker, and summarizes the DC circuit breaker cut-off topology proposed at home and abroad in recent years.On this basis, the mechanical, Z source structure,combined, cascade module, device combination DC circuit breaker topology and DC circuit breaker test circuit are discussed in detail.The topology principle, advantages and main problems of each aspect are discussed, the literature in the same field is compared. Finally, the possible future development direction and related problems of DC circuit breaker are put forward.

      • YANG Yulian, QI Linhai, WANG Hong, SU Linping, XU Yonghai

        Available online:February 16, 2020  DOI: 10.7500/AEPS20190605007

        Abstract:Traditional data missing reconstruction technology mostly relies on mathematical statistics method and prior knowledge combined with mechanism analysis to construct mathematical models. However, distribution network measurement data has high dimensional, time-varying, non-linear characteristics, high complexity, difficult characterization, and it is difficult to ensure high-precision reconstruction. In this paper, an unsupervised generation antagonism training method is proposed to extract data features independently and reconstruct missing data with dual semantic perception constraints. Among them, the reconstructed model based on 2D-CNN (two-dimensional convolution) and the two-dimensional gray image training of measurement data enhance the generalization ability and stability of the model. This method does not need prior knowledge distribution hypothesis and explicit physical modeling, and can effectively improve the accuracy of reconstructed data while guaranteeing maximum feature extraction. The validity of this method in reconstructing missing data is verified by the measured data.

      • CHENG Xin, XU Liang, ZHOU Shucan, LIU Zhenchao, LIN Yong, GONG Xianfu

        Available online:February 16, 2020  DOI: 10.7500/AEPS20190717008

        Abstract:As new energy is connected to the grid in a large scale, uncertainty caused by power supply has been higher than uncertainty of load demand. In addition, the probabilistic load flow of power system makes the management of operation department even more difficult. This paper proposes a novel method of energy storage configuration, which is based on trajectory sensitivity analysis of new energy output guarantee rate. Firstly, a probabilistic load flow over-limit equation of tested components is set up according to the uncertainties of new energy output. Secondly, a trajectory sensitivity analysis model of probabilistic load flow is built by setting the new energy output guarantee rate as a parameter. Thirdly, a strategy of energy storage configuration method is proposed to make the probabilistic load flow not exceed limit. In the meanwhile, power and energy requirements of energy storage are calculated for component-related nodes which have low trajectory sensitivity. Finally, the proposed method is simulated and verified on a practical power system in a peninsula of South China, which indicate that the method provides an effective reference for grid companies to develop energy storage planning.

      • JIANG Yicheng, CAO Hongxia, YANG Li, FEI Fan, LI Jing, LIN Zhemin

        Available online:February 16, 2020  DOI: 10.7500/AEPS20190602001

        Abstract:With the continuous expansion of renewable energy market in China, the pressure of government’s subsidy for renewable energy is gradually increasing due to the existing Feed-in Tariff (FIT). Renewable Portfolio Standard (RPS) has become the targeted renewable energy incentive mechanism in China currently. Firstly, the implementation of two main types of renewable energy incentive policy are discussed, including government-subsidized type and market-oriented type, and the FIT and RPS which are involved in the transformation are compared. Then, the overall framework, core design elements and supporting mechanisms of RPS are respectively introduced. Then, according to the implementation and research of RPS in various countries, the influences of RPS on the behavior of market participants and the overall performance of power market and green certificate market are summarized. Finally, the analysis shows that China should promote RPS in stages. The FIT-RPS double-track mechanism should be considered, with options on either FIT or RPS implemented for different types of power producers and various kinds of renewable energy sources.Meanwhile, supporting measures such as penalty and carbon emission trading should be constructed as well.

      • WU Hangfei, YANG Xiaodong, ZHANG Youbing, YANG Yu, PAN Hongwu, HUANG Xiaoming

        Available online:February 14, 2020  DOI: 10.7500/AEPS20190521001

        Abstract:This paper proposes an automatic demand response strategy based on event-driven mechanism, considering the diversity and richness of residential loads and great challenges brought by random electricity consumption behaviors to residential multimicrogrid system. The operational statuses of residential microgrids are divided into different events by using event-driven mechanism. The residential load is guided to fulfil consumption optimization considering price incentive and schedulable potential with the event-driven signal, so as to achieve automatic demand response. On this basis, the concept of energy level is introduced to the energy sharing model. By calculating the energy levels of each sub-microgrid in multi-microgrid system, the interactive power among microgrids is determined. The decoupling between inter-network and intra-network can decrease the complexity of energy sharing strategy. The numerical simulation results of a residential multi-microgrid system show that the proposed algorithm can effectively reduce operating cost of residential multi-microgrid system and improve optimization efficiency. This work is supported by National Natural Science Foundation of China (No. 51777193) and National Postdoctoral Program for Innovative Talents of China (No. BX20190126).

      • XIAO Bai, LIANG Xuefeng, JIANG Zhuo, NIU Xiangzhi, NIU Qiang, LI Jiefu

        Available online:February 14, 2020  DOI: 10.7500/AEPS20190521008

        Abstract:For the spatial load forecasting of urban power grids if the annual maximum value in the measured data of the cellular load is directly used, it is highly probable that the random fluctuation caused by errors such as measurement and communication will be brought into the prediction result, which leads to the problem of lowering the prediction accuracy. A method for determining the reasonable maximum value of cellular load by using complementary ensemble empirical mode decomposition and runs test technique is proposed. The method decomposes each class I cellular load sequence by analyzing the historical load data of the class I cells and the complementary ensemble empirical mode decomposition technique. Each class I cell obtains a set of intrinsic mode functions and uses runs test technique for each intrinsic mode function. The intrinsic mode function is tested for randomness, and the criterion for identifying the high-frequency component is established. The high-frequency intrinsic mode function that characterizes the random fluctuation of the cellular load is removed, and the remaining regularity and trend of the cellular load are analyzed. The intrinsic mode function is reconstructed to obtain the main component, and the maximum value of the main component is taken as the reasonable maximum value of the class I cellular load. Finally, the reasonable maximum value is used to predict the space load based on class I cells, and spatial load forecasting results based on class II cells are obtained by grid technology. The engineering example shows that the method is correct and effective.

      • Gong Jin-Xia, Liu Yanmin

        Available online:February 14, 2020  DOI: 10.7500/AEPS20190321010

        Abstract:In order to promote the application of the new generation of artificial intelligence in smart grid and energy internet, and realize the timely and effective utility of high- penetration renewable energy, the Deep Deterministic Policy Gradient (DDPG) method is applied in the optimal operation of Active Distribution Network (ADN) in this paper. The DDPG method can process the operation information of ADN and output the optimization scheme fast and continuously. In the proposed method, the goals of ADN optimal operation are minimizing the total voltage deviation and line loss of ADN, minimizing the variation of the power regulation of the microgrid(MG) to reduce the impact on the operation of the MGs in ADN, and balancing the tie-line power to reduce the impact on the distribution network. Then the DDPG-based optimal control of ADN are analyzed detailedly, including: sample data processing, return function designing and model training process. Finally, the effectiveness and superiority of the DDPG-based optimal control of ADN method are verified by the simulation results of the improved IEEE14-node example.

      • YANG Na, LIU Dunnan, LIU Mingguang, YE Bin, MA Jing, LI Xiaotong

        Available online:February 13, 2020  DOI: 10.7500/AEPS20190118007

        Abstract:Under the environment of transmission and distribution price reform, the profit mode of power grid enterprises has changed. Improving the precision investment capability of power grid enterprises is of great significance to the future development of power grid enterprises. Firstly, based on the Logistic model, this paper analyses the regional development stage according to the per capita electricity consumption index, and introduces the adaptability of regional economy and power grid development to revise the results. Secondly, the dynamic adjustment mechanism of transmission and distribution price is analyzed, and the evaluation model and process of power grid investment planning strategy are constructed. The differential investment strategy of power grid is designed in three typical modes: all new construction, all expansion and parallel construction. Finally, four typical cities are selected for calculation and analysis. The results show that: on the one hand, the cities in the post-rapid development stage should adopt all new investment strategies, on the other hand, the cities in the saturated growth stage should adopt all expansion models, and the optimal investment strategies of the cities in the rapid growth stage should be analyzed concretely. Based on the traditional investment decision-making, the strategy of grid differentiation investment considering transmission and distribution price verification and city development stage can provide reference for resource optimization of provincial power grid among cities.

      • LI Man, WANG Bing, QU Linan, TANG Zhen

        Available online:February 13, 2020  DOI: 10.7500/AEPS20190603011

        Abstract:The traditional high voltage ride through (HVRT) control strategy of photovoltaic (PV) grid-connected inverter (GCI) improves reactive power output at the cost of reducing active power, which is difficult to achieve a balance between grid-side current and DC bus voltage, and suppress the transient impact caused by sudden changes in voltage and current after fault removal. Based on the analysis about the transient power characteristics at high voltage, an HVRT control strategy that maintains active power output and adjusts the reactive current instruction is proposed in this paper. Firstly, a small-signal model is used to analyze the HVRT transient power characteristics, which reveal that the active power is constant and reactive redundancy is the key parameter for suppressing voltage recovery. A method for estimating the reference value of reactive current is then proposed according to the voltage surge amplitude. On this basis, by combining with active current control, the control capacity of the GCI under three different voltage surge amplitudes is discussed, and the HVRT control strategies are described respectively. Finally, the simulation and experiment are performed to verify the accuracy of the analysis about high-voltage transient power characteristics and the effectiveness of the proposed control strategy. Our control strategy adjusts the active and reactive current reference value adaptively according to the voltage surge amplitude without reducing the active power, thereby improving system voltage and current in an efficient and stable manner.

      • HU Jingzhe, WANG Xu, JIANG Chuanwen, CONG Hao

        Available online:February 13, 2020  DOI: 10.7500/AEPS20190611005

        Abstract:Considering the residents’ appeal to environment in the worst-hit areas, a comprehensive index carbon emission rights allocation scheme based on regional carbon emission balance is proposed in this paper. The allocation scheme is obtained by entropy method with indicators of the benchmark scheme in operation and regional carbon emissions. In order to study the effects of carbon price on emissions in power system, a three-stage optimal tiered emission pricing model is established, in which the first stage is unit commitment problem under normal conditions, the second stage is to find the worst N-1 fault scenarios, and the third stage is the solution of the optimal stepped carbon price. The model is solved by the column and constraint generation algorithm and dichotomy. Case study shows that when the emission task is small, tiered emission price can control carbon emissions with less carbon trading cost. Carbon emission right allocation scheme based on comprehensive indicators has a significant effect on balancing regional carbon emissions differences

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      • CHEN Qiaodi, ZHANG Xing, LI Ming, GUO Zixuan, LIU Xiaoxi, ZHAO Wei

        Available online:February 13, 2020  DOI: 10.7500/AEPS20190612007

        Abstract:In order to ensure the safety and power quality, the distributed generation system based on grid-connected inverters needs islanding detection function. The conventional islanding detection methods are not suitable for the grid-connected inverter with droop control, and the existing islanding detection methods designed for grid-connected inverters with droop control have to change the droop characteristics and exist non-detection zone. To solve the problems above, this paper proposes an islanding detection method for the grid-connected inverter with droop control based on impedance identification. The method injects voltage disturbance at the common coupling point, identifies the impedance by voltage and current disturbance signals, and then decides whether the islanding effect occurs according to the impedance variation. In order to improve the detection sensitivity, the harmonic disturbance injection is adopted to amplify the differences of characteristic parameters before and after islanding. In addition, the disturbance signals are extracted by recursive discrete Fourier transform, which improves the accuracy and timeliness of impedance identification. The experimental results verify the effectiveness of the proposed method.

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      • ZHANG Zhimei, HUANG Shaowei, MEI Shengwei, ZHANG Xuemin, JIANG Yefeng

        Available online:February 09, 2020  DOI: 10.7500/AEPS20190626005

        Abstract:The assessment of the vulnerability of transmission lines is an important step in the subsequent analysis and prevention of cascading outages. Existing vulnerability indices have problems including unclear physical meaning, no consideration of interaction and impact of multiple outages. To address the issues, this paper constructs a cooperative game framework of transmission lines. According to the result of the game, the loss caused by a fault chain is distributed properly to its member transmission lines as their vulnerabilities. This index can reflect the risk caused by the outage of the transmission line to the power grid, and therefore its physical meaning is clear. Faced with the non-superadditivity of the original cooperative game, the corresponding multi-objective programming is transformed into a two-stage optimization model, which copes with collective and individual rationality sequentially. The two-stage optimization model uses genetic algorithm and linear programming respectively. The case study of IEEE 39-node system verifies the validity of the proposed indices.

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      • Li Dongdong, Duan Weiyi, Lin Shunfu, Zhou Bo, Yao Yin

        Available online:February 08, 2020  DOI: 10.7500/AEPS20190726003

        Abstract:With the rapid growth of the amount of Electric Vehicles (EV), the demand for battery charging and discharging is also increasing correspondingly, but the growth rate of infrastructure construction is still relatively slow. The current situation is there is more EVs than charging piles. This has led to the problem of unbalanced distribution of charging piles. Based on this problem and combined with the real-time market demand, a user-guided EV-charging pile matching strategy is proposed. Firstly, an allocation function is established from the energy aggregator"s viewpoint and generate the information of available charging piles. Secondly, an optimization function is established from the user"s viewpoint to determine the geographical range of available charging piles. Finally, considering real-time electricity prices, EV users are encouraged to select appropriate charging piles for charging and discharging battery within the selected geographical range and effectively participate in power dispatch by updating subsidy fees. The Simulation results show that under the market requirements, the EV-charging pile matching strategy considers the two-way willingness of users and aggregators, and provides a decision basis for the rational distribution of charging piles.

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      • LI Xiaodong, ZHANG Zheren, XU Zheng, XU Yuzhe

        Available online:February 08, 2020  DOI: 10.7500/AEPS20190511001

        Abstract:Two key problems faced by meshed DC power grids are insufficient freedom of DC power flow control and DC line faults. In view of the above two problems, this paper proposes an integrated high voltage direct current (HVDC) circuit breaker with current flow control capability for DC power grid. Firstly, the basic structure and the working principle of the modular multilevel power flow controller (MMPFC) and hybrid HVDC circuit breaker are introduced. Then, the integrated HVDC circuit breaker is proposed, and the basic structure, the configuration principle, control mode and operation principle are introduced, respectively. Based on the analysis model of DC fault for single inverter, the capability to isolate the DC fault by integrated HVDC circuit breaker is analyzed. Finally, a four-terminal flexible HVDC grid is built on the PSCAD/EMTDC simulation platform to verify the current regulation capability and DC fault handling capability of integrated HVDC circuit breaker. The simulation results show that the integrated HVDC circuit breaker can control the DC power flow effectively and has the ability to deal with DC line faults.

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      • HUANG Wei, LIU Siqi, YE bo

        Available online:February 07, 2020  DOI: 10.7500/AEPS20190521003

        Abstract:A two-level model of station-network cooperative optimization is established in this paper. The upper-level model is an improved p-median model, and the decision variables are the location, capacity of energy stations and network layout. Considering the demand response characteristics of electric and heat loads, the lower model coordinates the interruptible load with the energy station supported by the power-heat-gas multi-energy flow. The GVNC algorithm is used to solve the model, which can improve the computational efficiency and obtain the global optimal solution. SOCR is used to transform the non-linear programming problem into a SOCP problem which is easy to solve. CCP is used to solve the problem of accuracy recovery after relaxation. The example shows that considering the influence of source-load interaction, the operation cost of the system can be effectively reduced, and the planned capacity of the energy station can be more economical and reasonable.

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      • WU Wenchuan, ZHANG Boming, SUN Hongbin, WANG Bin, YANG Yue, LIU Haotian, Lin Chenhui, WANG Siyuan

        Available online:February 05, 2020  DOI: 10.7500/AEPS20191030001

        Abstract:The traditional centralized control system in an active distribution network (ADN) would meet the problems of control agility, system reliability, mass communication and information privacy. This paper proposed a novel architecture of the energy management and operation regulation system for AND. Three are thee control levels in this hierarchical control system, including distribution controller for renewable energy resource cluster, optimization of the distribution networks incorporated with multi-clusters and coordination operation of integrated transmission & distribution networks. The paper mainly introduces the characteristics of the proposed system and some key technologies about cluster control, multi-level coordination optimization: (1) network analysis technology for ADN; (2) distributed cluster control technology; (3) active power and reactive coordination optimization technology for distribution network considering uncertainty; (4) distributed coordination and dispatching technology for integrated transmission and distribution networks. Finally, a pilot project is briefly described, and future researches are proposed.

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      • LIU Qiuhua, YUAN Hao, YANG Zhenglin, FAN Haifeng, XU Chunlei

        Available online:February 03, 2020  DOI: 10.7500/AEPS20191108007

        Abstract:The method of quantifying ancillary services as corresponding green certificates can motivate the enthusiasm of ancillary service providers, which is conducive to the consumption of renewable energy. After analyzing the additional increase of ancillary service caused by connecting renewable energy in the paper, the unfairness of current cost allocation way of ancillary service is pointed out. Then, based on the deviation theory of prediction curve, a green certificate calculation method for compensating the ancillary service by transferring the deviation between predicted curve and actual curve into the numbers of certificates. Furthermore, a quantitative method of green certificate allocation for frequency regulation ancillary service is designed. The effects and possible problems of this method are discussed.

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      • YANG Dongfeng, JIANG Chao, CAI Guowei, HUANG Nantian, LIU Xiaojun, HUANG Zheng

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190731014

        Abstract:with the development trend of the increasingly close electricity-heat connection and the maturity of AC/DC microgrid, a bi-level optimization model considering electricity/heat coupling for AC/DC hybrid microgrid is proposed. This model takes the annual investment cost, annual CO2 emission and annual transmission loss as the optimization objectives with giving consideration of the electric/heat power balance, self-government and other operational constraints as well. The upper layer is the capacity planning model of each device in the microgrid, and the lower layer determines the operation strategy of each device in the microgrid. Through the joint optimization of the upper and lower levels, the capacity configuration of each device in the micro-grid is studied. By comparing different planning scenarios, the influence of electricity/heat coupling system on optimization objectives is analyzed. Through annual equipment power output and power balance curve of typical days, the energy supply reliability of AC/DC micro-grid with electricity/heat coupling system are illustrated. Finally, the rationality and effectiveness of the model are verified.

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      • LI Xiaohua, LIANG Zipeng, FENG Jiawei, ZHANG Shaofan, CAO Jie, DING Xiaobing

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190310003

        Abstract:The DC transmission projects in China have long transmission distance and large span, and the crossing between AC lines and DC lines is increasing day by day. The power grid presents new fault type, that is touching fault for AC/DC transmission lines. There is lack of fault characteristics for touching fault and their influence on relay protection. Theoretical analysis on characteristics of touching fault for AC/DC transmission lines is made. AC/DC model is developed based on PSCAD/EMTDC simulation platform of detailed DC project. The characteristic quantities and key factors caused by touching fault are investigated, and potential challenges of which on operating characteristic of AC/DC protection are analyzed. Simulation results show that the fundamental frequency component introduced by touching fault can reduce the action rate of traveling wave protection for DC lines, there is a action dead zone in protection range between traveling wave protection and touching protection for AC/DC lines, and the sensitivity of AC distance protection is lower. This work is supported by National Natural Science Foundation of China (No. 51777079) and National Natural Science Foundation of China-State Grid Joint Fund for Smart Grid (No. U1766213).

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      • WANG Zhenhao, ZHAO Jiajing, CHENG Long, LIU Jie, LI Guoqing

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190619009

        Abstract:In view of the fact that the conventional semi-bridge modular multilevel converter (MMC) cannot block the fault current, and the existing MMC with the fault clearing capability takes too long to clear the fault, an active-grounded MMC (AG-MMC) topology with DC fault clearing capability is proposed. On the basis of conventional semi-bridge MMC, a current transfer branch is added outside the inductors on the upper and lower bridge arms of each phase of the converter, and a cut-off branch and an energy absorption branch are added at the DC outlet of the converter. When a bipolar short circuit occurs on the DC side of the MMC, the cut-off branch can effectively isolate the circuit breaker and the DC line. The current transfer branch can consume AC current and inductor current, and the energy absorption branch can quickly clear the fault current. The topology of AG-MMC and the process of realizing fault isolation and clearing are analyzed in detail, and the design and calculation method of key parameters are given. Finally, the two-terminal MMC and four-terminal MMC simulation systems is built by using RT-LAB OP5607 software. Comparative analysis shows that the proposed AG-MMC can clear faults within ten milliseconds, which has great advantages in terms of economy and practicality.

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      • YU Guoxing, HOU Rui, WANG Renxiao, SONG Huihui, QU Yanbin

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190603004

        Abstract:In order to improve the microgrid frequency regulation and power optimization performance, a two-layer control structure is proposed, in which the primary control converts the traditional power-frequency droop into the power-increment factor droop to accommodate this structure. The secondary control uses a consensus protocol to achieve the goals of frequency synchronization, frequency no-difference, and power optimization in a distributed manner. In addition, it is found through analysis that if only the saturator is used for power constraint, it will lead to a conflicts between frequency regulation and power optimization. To solve this conflict, a corresponding power constraint control method is proposed. Finally, The stability of the proposed control strategy in the system is demonstrated by the Lyapunov direct method and the effectiveness of the strategy is verified by a 5-node island microgrid simulation example.

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      • HAO Jinbao, ZHANG Yongjun, LIU Zehuai, ZHOU Lai, CHEN Boda, CHEN Jiachao

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190519002

        Abstract:Firstly, this paper proposes a load aggregator dispatching architecture, and a step function between the average air conditioning load and the difference of starting set temperature and ending set temperature in an hour is obtained by optimizing the fixed-frequency air conditioning load minutely, then a temperature difference-power model for air conditioning hourly scheduling is established by linearizing the feature of the step function above. Secondly, according to the feature of the air-conditioning temperature difference-power model, the applicability air-conditioning grouping method is proposed. Then, this paper proposes a non-cooperative game model of air-conditioning load aggregator for the multiple load aggregators in the distribution area, and introduces a continuous intermediate variable for the problem of control variables discretization in the game profit function, then set up a hierarchical optimization model of the game, the proof and solution method of the unique pure strategy Nash equilibrium solution for the hierarchical optimization of the game are given. Finally, the feasibility of the proposed method is verified by a simulation.

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      • MA Wenzhong, ZHOU Guanyu, SUN Peng, SAILIJIANG Gulipali, ZHANG Zi’ang, DONG Lei

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190411002

        Abstract:DC circuit breaker is a key element in VSC-MTDC system for DC fault clearance. For the stable operation of a DC breaker, a large DC reactor in series is required to limit the rising rate of the fault current, which could decrease the damping of critical poles, causing side effects to system stability. In this paper, based on a generalized VSC-MTDC small-signal model with DC breakers, modal analysis is performed to illustrate the main factors which could affect the stability. Furthermore, in the framework of H∞ mixed sensitivity theory, a robust damping controller is designed to improve the damping of the MTDC system. Finally, with a four-terminal VSC-MTDC model implemented in Matlab/Simulink environment, time simulations and root locus analysis are conducted and the results show that the proposed approach can efficiently suppress the DC oscillations, improve the system stability and address problems caused by strong disturbances and uncertainties.

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      • ZHANG Xueguang, ZHANG Yage, FANG Ran, CHEN Lie, XU Dianguo

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190216002

        Abstract:An improved control strategy for doubly-fed induction generator (DFIG) based on point of common coupling voltage disturbance compensation is proposed in this paper in order to solve the problem of grid-connected stability under weak grid. A unified impedance model of DFIG, including rotor side converter(RSC) and grid-side converter(GSC), is established in a synchronous reference frame. Based on the established impedance model, the transfer relationship between the point of common coupling voltage and the controller output is analyzed. The voltage disturbance compensation term is introduced into the rotor current loop and the grid-side current loop respectively to improve the converter control. The generalized Nyquist criterion (GNC) proves that the proposed method can effectively improve the grid-connected stability of DFIG under weak grid conditions. The analysis shows that the RSC and GSC improved controllers based on the point of common coupling voltage disturbance compensation can improve the impedance characteristics of DFIG so as to improve their stability under weak grid condition. Finally, the effectiveness of the proposed improved control method is verified by simulation.

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      • LI Baoqin, WU Junyong, SHAO Meiyang, ZHANG Ruoyu, HAO Liangliang

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190528009

        Abstract:In order to further improve the prediction accuracy of power system transient stability and give more refined evaluation results, the deep learning is combined with the power system transient stability, and based on the characteristics of the generator power angle "trajectory cluster" after fault removal. A refined power system transient stability evaluation model based on deep belief network (DBN) with different structures. The base classifier DBN of the model can effectively utilize the feature extraction ability of the deep architecture and fully exploit the nonlinear mapping relationship between the input features and the transient stability evaluation results. Experimental results on the New England 10-machine 39-node system show that this method is not only superior to the shallow learning framework, but also superior to the partial deep learning model. In addition, the ensemble DBN algorithm not only has higher prediction accuracy, but also can effectively evaluate the stability margin and instability level of the system; it shows strong robustness when some PMU information is missing and contains noise.

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      • WU Yongbin, WANG Su’e, XIONG Liansong, ZHANG Donghui, XU Zhao

        Available online:February 03, 2020  DOI: 10.7500/AEPS20190308009

        Abstract:The grid-connected power generation system integrated with photovoltaic (PV) and energy storage system (ESS) is taken as the research object, and multiple time-scales is used in the modeling ideas. Focusing on the main time-scale affecting the dynamic characteristics of system frequency—the DC voltage time-scale, this paper develops a DC time-scale dynamic model for the analysis of the system inertia and damping characteristics. On the basis of this model, the electric torque analysis method is used to analyze the main factors and their action laws on the inertia effect, damping capacity and synchronization characteristics from the physical mechanism level. The research results show that the dynamic characteristics of the system are determined by its control parameters, structural parameters and steady-state operation point parameters. The inertia effect and synchronization characteristics of the system are respectively affected by the proportional controller and integral controller in the DC bus voltage control loop. The damping capacity of the system is mainly affected by the frequency droop control in the energy storage device. The system dynamic characteristics will not be affected by the PV converter operating in the MPPT mode. In addition, the system dynamic characteristics are also affected by the structural parameters (such as line impedance, DC bus capacitance), and the steady-state operation point parameters (such as the AC/DC bus voltage level of the system) and the steady-state operation power (power angle). Finally, the correctness of the above analysis is verified by the simulation and experiment results.

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      • LOU Xiansi, MA Guang, GUO Chuangxin, WANG Luyu

        Available online:January 17, 2020  DOI: 10.7500/AEPS20190429011

        Abstract:In view of the multiple uncertain risk factors faced by the operation of power grid, this paper analyzes the necessity of risk coordination control from the perspective of risk development and dispatching mode. Based on the view point of risk coordination control, a system of risk coordination control for the whole process of power grid operation including four stages of medium and short-term, day-ahead, real-time and post-contingency is proposed. The risk optimization models, control measures and coordination strategies in each stage are elaborated in detail. A solution based on five-tier software framework is proposed and key technologies for supporting system application are discussed. Finally, the preliminary implementation of the whole process risk coordination control system in the Zhejiang Power Grid is introduced. The results of theoretical analysis and engineering practice show that the proposed system and framework in this paper can adapt to the “open, fair and just” power dispatching, coordinate the risk control decisions in each stage and realize the step-by-step tracking and rolling control for the operation risk of power grids.

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      • LI Zhen, SHENG Wanxing, DU Songhuai, LI Penghua, WANG Jianhua

        Available online:January 16, 2020  DOI: 10.7500/AEPS20190812008

        Abstract:Supplying power for loads and realizing the connection of distributed generators (DGs) are the essential functions of the flexible distribution equipment (FDE). Consequently, the control of AC port in FDE is intensely crucial. Aiming at the voltage control of AC port in FDE, the three-phase voltage is controlled independently based on the virtual synchronous generator (VSG) control, and its dynamic performance is improved by cascaded quasi proportional-resonant (PR) voltage outer-loop and current inner-loop. Furthermore, the influence of output current of AC port in FDE on the voltage is analyzed in detail by taking single-phase voltage as an example. And the current feedforward control strategy is proposed to ensure the voltage stability of AC port while loads and DGs are varied. The output impedance of AC port is obtained by the impedance modeling method, and the stability of AC port in FDE is analyzed by generalized Nyquist stability criterion when FDE supplies power for loads and realizes the DGs’ connection. Finally, the correctness and effectiveness of the proposed control strategy are verified by simulation and experiment.

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      • WEI Nengqiao, ZHOU Niancheng, LUO Yongjie, WANG Qianggang

        Available online:January 15, 2020  DOI: 10.7500/AEPS20190626004

        Abstract:DC circuit breakers (DC circuit breaker,DCCB) need high operate speed and current break ability because fault current of flexible dc grid rising fast and conventional half-bridge Modular Multilevel Converters are short of over current resistant ability. Fault current limiter (fault current limiter,FCL) can retrain fault current when short-circuit fault is identified, and reduce the requirement of DCCB. This paper calculate the fault current and voltage stress of FCL with different type of fault limiting impedance, and the change with parameters are analyzed; a parameters optimization method of fault limiting impedance which optimization objectives are breaking current of DCCB and cost of FCL is established. The method proposed in this paper can adjust to different flexible dc system and type of current limiting impedance, and optimize parameters with constraints. Works in this paper are verified through PSCAD/EMTDC simulation.

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      • HU Changbin, WANG Haipeng, LUO Shanna, ZHOU Jinghua, SHI Yuntao, MA Rui

        Available online:January 15, 2020  DOI: 10.7500/AEPS20190805002

        Abstract:Abstract: Aiming at the problem of bus voltage control in DC microgrid, a dynamic compensation control strategy based on robust disturbance observer is designed to complete voltage compensation of DC-DC converter. Firstly, based on the DC microgrid system architecture, the theoretical analysis of the bus voltage fluctuation is carried out. Secondly, the state space mathematical model of the DC-DC converter of the DC microgrid system is established, and the input and output relationship of the control system is obtained. According to the robust dual-mass decomposition and Youla"s parameterized stability controller theory, the proposed robust disturbance observer control architecture is proved. The model matching theory is applied to compensate the output value generated by the current disturbance. The voltage loop compensation controller Q(s) is solved by a linear matrix inequality (LMI) method, and the current loop compensation controller H(s) is designed according to the dynamic structure diagram of the DC-DC converter. The results of semi-physical experiments show that the architecture can improve the dynamic performance of DC-DC converter without changing the structural parameters of the original system, and suppress DC bus voltage fluctuation caused by load switching, power fluctuation and AC side load imbalance, and enhances the robustness of the system.

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      • ZHENG Tao, WU Qiong, LYU Wenxuan, LI Rui, XU Lie

        Available online:January 15, 2020  DOI: 10.7500/AEPS20191114003

        Abstract:DC faults in the flexible DC distribution network could easily lead to overcurrent, which seriously threaten the safe operation of the network. FBSM-MMC blocking is mostly used to cut off the fault current in the distribution network which based on the FBSM-MMC. But the blocking will cause power outage of the whole network for a moment, which is not conducive to the reliability of the power network. Aiming at the problem, a protection scheme combined by the control of MMC and the protection of DC network is proposed, which consists of three stages. After a short-circuit fault occurs, the output DC current of the inverter will be limited to 1.2pu by the control of MMC(Stage 1). The faulty line is identified according to the synchronous zero-crossing characteristic at both ends of each line(Stage 2). A fault isolation scheme which contains the cooperation of DC circuit breakers and high speed switches is proposed(Stage 3). The switch in the faulty line can be turned off quickly with the associated DC breaker disconnected and the associated MMC’s output current reduced to 0. Finally, the feasibility of the proposed protection scheme and the isolation scheme is verified by a large number of simulations in PSCAD/EMTDC.

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      • SHEN Jun, LIU Wei, LI Hucheng, LI Na, WEN Zhen, YIN Minghui

        Available online:January 15, 2020  DOI: 10.7500/AEPS20190521007

        Abstract:Aiming at the problem of frequency and voltage static deviation caused by primary control of distributed generation in microgrid, a distributed secondary optimal control based on reinforcement learning local feedback method is proposed, which addresses the need of frequency recovery and voltage adjustment by just using local information. Firstly, according to the demand of microgrid economy, frequency and voltage control and the comprehensive performance of distributed generation (environmental benefit, economic benefit and technical benefit), a local reward is defined to coordinate the frequency recovery and voltage regulation of multi-microgrid. Secondly, in view of the actual operation of the power grid, while satisfying the balance between supply and demand, the multi-agent reinforcement learning algorithm is used to optimize and modify the global reward feedback, so that the frequency deviation can be eliminated asymptotically and the stable operation of the microgrid can be guaranteed. Finally, the effectiveness and adaptability of the proposed control are verified by the analysis of case study.

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      • ZHAO Chengyong, SONG Bingqian, XU Jianzhong

        Available online:January 14, 2020  DOI: 10.7500/AEPS20190626003

        Abstract:The structure and operation modes of flexible DC grid are diverse, and there are strong coupling relationships among various power electronic devices. The fault characteristics are complex, coordination control is difficult, and proactive control of fault current still faces great challenges. Based on the fault current development mechanism of flexible DC grid, the paper compares and summa-rizes the fault characteristics of AC and DC grids, and illustrates the necessity and possibility of active control of fault current in flexible DC grid. The basic scheme of active control scheme for fault current of flexible DC grid is determined. Principles; summarizing domestic and foreign research results, classifying active control schemes according to selectivity principle and suppression principle; taking several typical schemes as examples, analyzing the characteristics of different types of active control schemes, and simulating them in PSCAD/EMTDC Verification, comparing and summarizing the characteristics of different active control schemes. The results show that the active control of fault current is coordinated by the source side and the network side equipment, which has a good development prospect.

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      • LI Yalou, SUN Qianhao, MENG Jingwei, MU Qing, ZHANG Xing

        Available online:January 14, 2020  DOI: 10.7500/AEPS20190715001

        Abstract:The electromagnetic transient (EMT) simulation of hybrid modular multilevel converter (MMC) is an important basis for the related researches about hybrid MMC. However, because there are various kinds of sub-module (SM) circuits can be employed in hybrid MMC, and a lot of power electronic switches are included in each SM circuit, the detailed EMT model of hybrid MMC will reduce the simulation efficiency seriously. In view of this background, the unified dynamic averaging equivalent model of the series structure of the various SM circuits is proposed in this paper based on the switching function and the dynamic characteristic of capacitor. Besides, a unified terminal high efficiency EMT model of hybrid MMC based on the proposed dynamic model of the series structure is also presented and analyzed. The proposed unified model in this paper not only is convenient but also has the great simulation accuracy and efficiency, which is especially important for a research tool. The simulation accuracy and efficiency of the proposed model are validated by the comparison with the detailed model in ADPSS.

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      • ZHANG Fuxuan, GUO Xianshan, WANG Nannan, TIAN Jie, LU Yu, DONG Yunlong

        Available online:January 14, 2020  DOI: 10.7500/AEPS20190225001

        Abstract:Large-capacity renewable energy is transmitted through bipolar voltage source converter based high voltage direct current (VSC-HVDC) system in the island mode, which has broad application prospects. This paper analyzes the power surplus characteristics under the non-fault-pole overload and DC overvoltage conditions. Then the scheme of grouped AC energy dissipation resistor is proposed. The power surplus control strategies are designed in the cases of converter fault in sending end and DC overvoltage. By accurately switching the grouped AC energy dissipation resistor, the outage of bipolar VSC-HVDC system caused by power surplus is avoided. The proposed two power surplus control strategies are verified in real-time digital simulator (RTDS) and EMTDC simulation system of four-terminal VSC-HVDC power grid. Simulation results show that the proposed strategies can realize fault ride-through under the condition of power surplus, and the expansion of fault coverage can be avoided.

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      • LI Botong, YANG Xinlu, LI Bin, LYU Huijie

        Available online:January 14, 2020  DOI: 10.7500/AEPS20190418004

        Abstract:The isolation and recovery of faults is the key issue to guarantee the supply reliability in the DC distribution network. Using converters with fault clearance capability and isolating switches to achieve fault current blocking and isolation has become an important development direction of DC distribution network. From the three aspects of protection technology and fault location, fault isolation and fault recovery, this paper summarizes the research status of fault processing technology based on blocking converters in the DC distribution network. Then the problems and difficulties of fault processing technology based on blocking converters in the DC distribution network are sorted out. Finally, the development trend of key technologies in this research direction is prospected.

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      • LI Yan, HuangYu, GONG Yanfeng, PanXudong

        Available online:January 14, 2020  DOI: 10.7500/AEPS20190425008

        Abstract:For MMC-based flexible DC grid with symmetric monopolar topology, this paper studies the evolution law of fault currents of single pole to ground fault and bipolar fault, and thus reveals that non-faulted line charging and fault waves are respectively the main reasons for the overvoltage of single pole to ground fault and bipolar fault. Then, a three-terminal flexible DC grid is used for simulation and verification, and the influences of different factors on overvoltage are analyzed. The results show that the fault resistance has a great effect on the peak value of the overvoltage, while the converter blocking, grounding scheme and line protection have little effect. Finally, the overvoltage of single pole to ground fault and bipolar fault are summarized and compared.

      • XUE Shimin, LIU Cunjia, LI Zheng, LU Junchi, ZHU Xiaoshuai

        Available online:January 14, 2020  DOI: 10.7500/AEPS20190529006

        Abstract:At present, the protection schemes of DC microgrid mostly depend on the fast breaking ability of DC circuit breakers at both ends of the line and the reliability of communication equipment. However, at this stage, the cost of DC circuit breakers is high, and the communication between the two ends of the line will greatly increase the construction and operation cost of DC microgrid. Based on the above background, this paper proposes a single-ended ranging protection technology based on control and protection cooperation for the four-terminal ring DC microgrid system. This method can be divided into two stages: fault control and protection implementation. In the phase of fault control, the fault current of DC line is controlled to be zero by changing the active control strategy of voltage source converter (VSC) itself and the external controllable elements. In the phase of protection implementation, based on the periodicity (20 ms) of the output voltage on the DC side of VSC after active control and the controllability of power electronic components, the unique loop between VSC and fault point is constructed. Then the single-ended fault location without error can be realized based on the traditional R-L algorithm. Differential fault location will lead to continuous zero-crossing of line current. On this basis, fault isolation can be achieved by fast disconnector. Based on the idea of control and protection cooperation, this method eliminates the interference of terminal current in single-end fault location of ring network system, and there is no need to configure DC circuit breakers at both ends of the line. Fault isolation can be achieved only by using fast disconnector and fault control strategy to cooperate logically in time sequence. Finally, a four-terminal ring DC microgrid system model is built on the PSCAD/EMTDC simulation platform, which verifies the effectiveness of the control and protection scheme.

      • HUANG Xinyu, ZHANG Jiakui, XU Qianming, CHU Xu, WANG Yichao

        Available online:January 14, 2020  DOI: 10.7500/AEPS20190730005

        Abstract:To solve the problem of lack of freedom of power flow control in multi-terminal DC transmission system, a modular DC power flow controller (DCPFC) is proposed, which adopts modular structure to facilitate the expansion of multiple lines and has the ability of DC fault current limiting. Firstly, the topology of DCPFC is introduced, and its equivalent circuit model is established, while the principles of power flow control and fault current limiting are described. Then the power transfer characteristics of bridge arm of DCPFC in the power flow control mode are analyzed, and the power balance mechanism of bridge arm based on AC circulation is studied. On this basis, the power distribution control and power balance control methods of DCPFC are proposed, and their control strategies in the fault current limiting mode are illustrated. Finally, a three-terminal DC transmission system is built in PLECS simulation software to verify the effectiveness of DCPFC in the conditions of power flow distribution, power flow reversal, power step and fault current limiting.

      • HAO Liangliang, LI Weijie, WANG Zhuoya, GU Yaqi, WANG Guang

        Available online:January 13, 2020  DOI: 10.7500/AEPS20190729015

        Abstract:As an effective means to support the adoption of high proportion of renewable energy, MMC-HVDC has become an important direction of power grid development. The pole-to-pole fault is the most serious fault in transmission lines. At present, state equations of DC system are usually written in the s domain, and then fault currents are solved based on the Inverse Laplace Transformation,while a practical engineering calculation method for fault current is needed urgently. In this paper, Zhangbei MMC-HVDC grid is taken as the research object, the fault characteristics and coupling mechanism of DC polo-to-pole fault are analyzed firstly. On this basis, the two ends of the fault lines near the valve side are regarded as two-ports respectively, the relationship between the fault currents and the voltages of the two-ports are analyzed. Secondly, based on the idea that the voltage of the two ports of the positive and negative lines does not change much, the annular MMC-HVDC grid is simplified to a two-terminal system or an open system. The practical calculation method of fault line current is obtained to calculate fault current directly, while it is no longer necessary to solve the high order Inverse Laplace Transformation. Finally, the feasibility and efficiency of the practical calculation method are verified by comparing with the electromagnetic transient simulation results.

      • Song zhao, SHU Dewu, yan zheng, Luo Xiao

        Available online:January 13, 2020  DOI: 10.7500/AEPS20190805005

        Abstract:In order to accurately simulate dynamics of large-scale AC/DC grids and interactions between individual components, a simulation method with high precision and efficiency is highly required. To revolve these issues, a multi-domain simulation method combining phasor- and time-domain models is proposed. In this method, the DC grids are partitioned into the phasor subsystem, which are presented by their phasor models. This method can adopt large time-step to improve the efficiency while the accuracy is guaranteed. Further, a multi-domain interface model between different subsystems is proposed. The interface model can reflect both instantaneous and wide-band phasor waveforms simultaneously. Finally, a practical AC/DC system integrating four terminal VSCs in China has validated the effectiveness of the proposed method.

      • LI Binbin, ZHANG Yujie, ZHANG Shuxin, ZHAO Xiaodong, XU Dianguo

        Available online:January 13, 2020  DOI: 10.7500/AEPS20190730002

        Abstract:As the key equipment for the future DC power grid, the high-voltage and high-capacity DC/DC converter has become the hot research topic in recent years. This paper proposes a hybrid DC/DC converter topology combing thyristors with half-bridge sub-modules. The hybrid DC/DC converter can block the short-circuit faults on the high-voltage and low-voltage sides by latching sub-modules and thyristors, and has the advantages of low cost and high efficiency. The working principle, fault protection mechanism, control strategy, parameter design and economy of the topology are analyzed and demonstrated. Finally, the feasibility of the proposed topology and control strategy are verified by simulation results based on MATLAB/Simulink.

      • Cui Liangjie, SUN Yi, LIU Yaoxian, WEN Yafeng

        Available online:January 13, 2020  DOI: 10.7500/AEPS20190225006

        Abstract:Load monitoring is an important part of intelligent electricity consumption. A non-intrusive load decomposition method considering time-phase behavior is proposed considering the problem that existing low frequency non-intrusive load decomposition methods require more priori information and have lower accuracy for load with similar or low power. Firstly, power data of the load device is clustered to construct a load state template.An intelligent optimization method for the typical behavior time period that does not require a specified number of time periods is proposed. Load state behavior law is extracted by time-phase to construct a load behavior template. On the basis of the traditional power characteristics, considering the two dimensions of probability and time, the time-phased state probability factor (TSPF) is introduced into the objective function as a new load characteristic, and the load decomposition is realized by multi-feature genetic optimization iteration. Finally, the validity and accuracy of the method are verified on the public data set.

      • LI Guoqing, BIAN Jing, WANG He, SUN Yunhe, WANG Zhenhao

        Available online:January 13, 2020  DOI: 10.7500/AEPS20190607003

        Abstract:Fault current limitation in DC power grid has become one of the important problems that must be faced and urgently solved in related fields. Most of the existing fault limitation methods adopt single component. In order to fully limit the rising rate and peak value of fault current, this paper proposes a fault limitation and optimal configuration method combining the characteristics of DC reactor and capacitive current limiter. Firstly, based on the fault equivalent circuit of modular multilevel converter, the necessity of installing fault current limiter is analyzed from two aspects of limitation principle and action sequence. Secondly, the limitation characteristics of inductance and capacitance to fault current are calculated and analyzed, and the equivalent circuit and solution method are extended to DC ring grid. The optimal configuration model is constructed with the objective of fault current and DC reactor. Finally, the optimization results are applied to PSCAD/EMTDC simulation model. Compared with the scheme using DC reactor only, the configuration results can further reduce 40% of the fault current without prolonging the fault clearance time. It is verified that the combination of DC reactor and capacitive current limiter can significantly reduce the fault current and the breaking capacity of DC circuit breaker.

      • LI Zhendong, AN Haiqing, FAN Xiaowei, YANG Dawei, YANG Minxiang, ZHANG Jianpo

        Available online:January 13, 2020  DOI: 10.7500/AEPS20190715003

        Abstract:Abstract: The symmetrical and bipolar flexible high voltage direct current(HVDC) transmission system has higher transmission capacity and higher reliability than the monopole system. Therefore, it is gradually being applied to practical engineering. In view of AC/DC outlet ground faults of modular multilevel converter in bipolar systems, the transient characteristics of voltage and current after converter fault blocking were studied, and the mathematical analytical formula of the fault component was derived. The research results show that a single phase-to-ground fault in the AC outlet lead to the up-arm of blocked converter on the non-fault phase over-voltage and the lower-arm over-current on the non-fault phase. And the DC bias on the AC-side current causes the fault phase short-circuit current to have no zero-crossing. When the DC outlet occurs a pole-to-ground fault, the short-circuit current of the bridge arm of the blocked converter is mainly composed of the steady-state current injected by the AC system and the circulating current between the upper and lower arm. A phase-selective trip protection strategy is proposed for this special fault characteristic of single-phase ground fault at AC outlet. The problem that the AC circuit breaker cannot be normally opened when the zero-crossing point of the fault current does not exist is solved.A simulation model of the zhangbei flexible DC grid was built. The simulation results show that the analysis of the fault characteristics in the converter outlet is accurate and the proposed strategy is effective and feasible.

      • LI Guoqing, LIU Xianchao, ZHANG Song, JIANG Tao, CHEN Houhe, LI Xue

        Available online:January 13, 2020  DOI: 10.7500/AEPS20190601001

        Abstract:The three wires bipole structure based high voltage direct current (TWBS-HVDC) system can greatly enhance the transmission capacity of the DC lines, which has become an effective method for converting AC line into DC line and lines capacity improvement. Aiming at the difference between TWBS-HVDC and bipole direct current system in connection ways, a DC side short-circuit fault current calculation method for TWBS-HVDC system was proposed. Firstly, the transient equivalent model of TWBS-HVDC system was established based on MMC transient equivalent circuit. The number of independent circuits and the order of dynamic components in the transient equivalent circuit were taken as the standard, all DC faults were classified into three categories, and the state equations of each kind of fault was analyzed and deduced. The analytical expression of fault current was obtained by solving the eigenvalue and eigenvector of coefficient matrix in the state equation. Finally, a two-terminal TWBS-HVDC system simulation model was established in the MATLAB/Simulink digital simulation platform, and the simulation results validated the effectiveness and accuracy of the short-circuit fault state equation solution method on the DC side of the TWBS-HVDC system proposed in this paper, which can provide a scientific basis for the selection of system main circuit parameter and the setting of relay protection action time.

      • LIU Shuo, SU Jianhui, LAI Jidong, ZHANG Jian, WANG Haining

        Available online:January 10, 2020  DOI: 10.7500/AEPS20190408002

        Abstract:The calculation of voltage gain-frequency characteristic is vital in the design of LLC resonant converter. The LLC converter have various operation modes due to the existence of nonlinearity in the rectifier part of the converter. And the voltage gain-frequency characteristic is closely related to operation modes. The PO mode is a discontinuous conduction mode (DCM), which is beneficial to reduce switching losses of the converter. However, the voltage gain-frequency characteristic of converter in the PO mode is hard to be worked out because it involves complex computations. On the basis of subinterval analysis method, this paper analyzes the operation characteristics in the PO mode of LLC resonant converter, and deduces a simplified and high-accuracy calculation formula of voltage gain. In addition, the parsing and concise expressions of power boundary conditions both in DCM mode and PO mode are provided in accordance with nonlinear characteristic in rectifier part of the converter. A simulation model and an experimental prototype of LLC converter are developed, and the simulation and experiment results verify the validity of the deduced voltage gain formula and power boundary condition.

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      • XU Fangwei, WANG Chuan, YANG Honggeng, XU Lin, ZHAO Jinshuai, WANG Yang

        Available online:December 27, 2019  DOI: 10.7500/AEPS20190824004

        Abstract:All the existing quantification methods of harmonic responsibility of distributed multiple harmonic sources use the external port current (hereinafter referred to as the port current of harmonic source) of the harmonic source equivalent circuit (Norton equivalent model in common use) to calculate the harmonic contribution of the harmonic source to the concerned bus. Since the harmonic source port current is constrained by the Kirchhoff’s law, as long as the harmonic source port current changes in the power grid, the harmonic contributions of all harmonic sources to the concerned bus will change accordingly. However, the harmonic source port current is usually the result of the coupling of harmonic source and background harmonic, so the harmonic contributions calculated by this current cannot truly reflect the harmonic emission level of the harmonic source. Therefore, this paper quantifies the harmonic responsibility of each harmonic source to the concerned bus by harmonic source current itself rather than harmonic source port current. The proposed method directly solves the complex harmonic voltage contribution of each harmonic source to the concerned bus, and it does not need to solve the harmonic transfer impedance of the harmonic source to the concerned bus, which reduces the effect of cumulative errors, can more fairly and reasonably reflect the harmonic responsibility of each harmonic source. The effectiveness and accuracy of the proposed method are verified by simulation and experimental example.

      • LI Bin, WANG Chenyang, HE Jiawei, YE Shilei

        Available online:December 24, 2019  DOI: 10.7500/AEPS20190418012

        Abstract:In order to eliminate the adverse effects of conventional current-limiting reactance on the operation stability of DC system and the breaking speed of DC circuit breaker, the bridge current-limiting solid-state circuit breaker has achieved excellent performance of both adaptive fault current limiting and breaking. However, the DC bias power supply in the bridge circuit has the shortcomings of no overcurrent protection and relatively high power capacity and investment cost. For the bridge-type current-limiting solid-state circuit breaker, this paper designs a DC bias power supply based on three-phase half-wave rectifier circuit. The method of selecting the parameters of bias power supply and setting the voltage is put forward, which effectively reduces the number of power electronic devices, realizes the over-current protection circuit of bias power supply, and reduces the designed capacity and cost of bias power supply. The prototype experiment and simulation examples verify the advantages of the proposed bias power supply of self-adaptive current-limiting solid-state circuit breaker.

      • FENG Zhuocheng, WAN Kaiyao, JIANG Tong

        Available online:November 30, 2019  DOI: 10.7500/AEPS20190301001

        Abstract:In order to calculate the steady voltage stability margin rapidly and precisely, an algorithm based on asymptotic numerical method is proposed. By analyzing the equations formulated by the voltage collapse point, the general formula of the high-order partial derivatives of the voltage stability boundary are obtained. Based on the asymptotic numerical method, the relationship between the fitting error and the boundary area is analyzed. The method avoids the multiple traditional flow calculation with higher accuracy and lower time cost.On the other hand, the factor table of the existing coefficient matrices can be reused when calculating the high-order partial derivatives, which decreases the calculation burden. The related applications based on the method are presented. Testing examples based on IEEE 118 node system are established to verify the effectiveness of this method at length.

      • WANG Yibo, CAI Guowei, LIU Chuang, GUO Dongbo, WANG Peng, ZHU Bingda

        Available online:November 19, 2019  DOI: 10.7500/AEPS20190409006

        Abstract:Dynamic voltage restorer (DVR) is a power electronic device connected in series with source and load, which is used to rapidly compensate voltage fluctuation in the power system. However, due to the energy storage equipment, the conventional DVR based on voltage source inverters (VSIs) has some shortcomings. And DVR based on direct AC/AC conversion with pulse width modulation (PWM) has the shortages of commutation problem and voltage balance of flying capacitor. Therefore, this paper proposes a single-phase DVR based on bipolar direct AC/AC conversion. The AC/AC converter topology with PWM used in the proposed DVR has the characteristics of common grounding between the input and output ports. In addition, the proposed DVR can achieve bipolar voltage regulation under a simple control strategy and solve the commutation problem during operation effectively. In order to verify the engineering value of the proposed DVR, a 1 kW experimental platform has been built to verify its rationality and effectiveness on the basis of theoretical analysis.

      • ZU Guoqiang, XIAO Jun, MU Yunfei, ZHU Xiaohui, YAO Ying, JI Dalong

        Available online:November 19, 2019  DOI: 10.7500/AEPS20190617001

        Abstract:The China urban power grid is evolving to smart distribution grid, of which the operating circumstance will be more complicated. Security region is a new method for the distribution system operating. This paper studies the smart distribution system security region (DSSR) from the view of user load, taking two main elements into account, which are distributed generation (DG) and demand response (DR). Firstly, it analyzes and formulates the characteristics of security operating for distribution systems with DG and DR then the DSSR with DG and DR is modeled. It observes the DSSR 2D sections on case grids and studies the mechanism of DG and DR on DSSR, based on which the guidance for the distribution system planning and operating is proposed. The DSSR in this paper is consistent with the usual practice of dispatchers and could be a useful tool of the security monitoring and analysis for urban power grids, in which the user load service is more important than the service of DG and DR.

      • LIANG Deliang, LIU Yibin, KOU Peng, CAI Shengliang, ZHOU Kun, ZHANG Mingkang

        Available online:November 04, 2019  DOI: 10.7500/AEPS20190507007

        Abstract:Intelligent distribution transformer is a key device to construct the new generation of intelligent distribution network with the rapid development of smart grid. This paper analyzes the main functions of the intelligent distribution transformer combining development trend of the distributed generation of renewable power and AC/DC hybrid distribution power system, and states that the key of realizing the intelligent distribution transformer is the high controllability, which can be achieved by utillizing the power electronic devices. Based on this, the analysis shows that the power electronic transformer (PET) and hybrid distribution transformer (HDT) are two alternative circuit schemes for the intelligent distribution transformer. The basic working principle of PET and HDT are introduced, and the several typical topologies of the intelligent distribution transformer based on PET, HDT and the extended HDT are presented and their characteristics are analysed. Based on a specific application scenario in the distribution network, the working principle, reliability, economy, controllability of the intelligent distribution transformer based on PET and HDT are compared, and the variation trend of each performance is presented when the ratio of the conversion power is increasing. Finally, the future developmemnt trend of the intelligent distribution transformer are analysed.

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      • LONG Kaihua, LI Xiaoqian, LI Ziming, XIE Xiaorong, CAI Wei, HUANG Jinkui

        Available online:November 01, 2019  DOI: 10.7500/AEPS20190408013

        Abstract:In order to prevent the trip of modular multilevel converter (MMC) due to block, the rising speed of DC short-circuit current should be limited. The active current-limiting control of MMC is a new current-limiting method, which can limit the DC short-circuit current by reducing the discharging time of capacitor without extra cost. The existing calculation method of DC short-circuit current cannot reflect the change of circuit structures and parameters caused by active current-limiting control. This paper proposes a calculation method of DC short-circuit current considering active current-limiting control of MMC. A duty circle index for discharging state of capacitor is introduced to represent the effect of active current-limiting control on DC short-circuit current. The state equation of DC short-circuit current is built based on state space averaging method, and the time-domain analytical expression of DC short-circuit current is given. The effectiveness of the proposed calculation method is validated by the simulation results based on PSCAD/EMTDC.

      • XIE Jiping, ZHANG Wen, YANG Hao

        Available online:October 31, 2019  DOI: 10.7500/AEPS20190403005

        Abstract:Compared with the conventional single-layer connection mode of ultra-high voltage direct current (UHVDC) system, the hierarchical connection mode improves the ability of AC system in acceptance and providing voltage support for multi-infeed UHVDC systems from the aspect of grid structure, and it makes power flow distribution and control more flexible and reasonable. In order to make full use of the fast power adjustment capability of UHVDC systems in the hierarchical connection mode, and avoid or reduce the economic loss caused by the load shedding during the medium-term and long-term voltage instability process, this paper proposes a coordinated control method for AC/DC power systems with hierarchical connection of UHVDC systems. Firstly, based on the quasi-steady model of UHVDC system in the hierarchical connection mode, this paper deduces the analytical expressions of sensitivities of the converter bus voltages with different control mode of UHVDC systems to the inverter transmission powers of UHVDC systems in hierarchical connection mode. Secondly, the voltage trajectory prediction model of AC/DC system is established based on the derived sensitivities. Finally, considering modulations of the DC current and the extinguishing angle of high and low ends of the inverter, a receding horizon optimization model of coordinated voltage control is constructed based on the predicted trajectory. The hierarchical DC injection powers and the voltage control means of AC system are coordinately controlled. The simulation analysis of the planning system of Shandong power grid shows that the proposed method can effectively coordinate the distribution of DC transmission power in AC grid, which enhances the system voltage stability and reduces the load shedding loss.

      • ZHANG Yanke, LIU Yuan, JI Changming, ZHANG Jiaxin

        Available online:October 30, 2019  DOI: 10.7500/AEPS20190411007

        Abstract:In the operation optimization of cascade hydropower reservoirs, it is a usually simplified way that neglecting time-lags of flow routing and regarding the upstream reservoir outflow as the downstream reservoir inflow, which have an impact on accuracy of operation scheme when time-lag is big enough. In order to reduce the effect of time-lags of flow routing, firstly, the relationship between upstream reservoir outflow, local inflow, downstream reservoir water level and downstream reservoir inflow is quantized based on the principle of linear space. Secondly, the artificial neural network, Kmeans and Relief methods in date mining are comprehensively applied to solve and determine the mapping relationship. And then, a short-term generation optimization model of cascade hydropower reservoirs considering time-lags of flow routing is established. Finally, to verify the feasibility and effectiveness of the model, it is applied to solve the operation optimization of cascade hydropower reservoirs in Yalong River, and the results show that the established model can considerably improve the accuracy of short-term optimal operation plan. So it can give full play to the utilization efficiency of water resources, and provide reference for actual operation.

      • WANG Shouxiang, GUO Luyang, CHEN Haiwen, DENG Xinyu

        Available online:October 21, 2019  DOI: 10.7500/AEPS20190625010

        Abstract:Aiming at the limitation of using single equipment features for load identification, we proposed a non-invasive load identification algorithm based on feature fusion and deep learning. Firstly, The V-I trajectory image features and power numerical features are extracted by analyzing the high frequency sampling data of the equipment. Then the fusion of V-I track image features and power numerical features is realized by using the advanced feature extraction ability of ANN. Finally, the BP neural network is trained to identify equipment by using fusion feature as the new feature of the equipment. We used PLAID data set to verify the identification performance of the algorithm, and compared the performance of different classification algorithms for feature fusion and load identification ability. The results show that the proposed algorithm makes use of the complementarity of different features, overcomes the disadvantage that V-I track features cannot reflect the power of the equipment, and improves the load identification ability of V-I track features. In embedded devices, the computing speed of proposed algorithms can reach the millisecond level.

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      • ZHAO Yitong, WANG Huifang, HE Benteng, XU Weina

        Available online:October 21, 2019  DOI: 10.7500/AEPS20190507001

        Abstract:In order to improve the economy of the investment and operation of user-side battery energy storage and reduce the cost of user power consumption, a rolling optimization method of user-side battery energy storage configuration and operation scheduling is proposed. Firstly, the benefit of users after installing energy storage and the constraints of energy storage operation are analyzed. Then the energy storage configuration optimization model, the energy storage optimization model before month and the rolling optimization model for intra-day operation are constructed and solved by CPLEX solver. Energy storage performance constraints are added to the model, which can effectively reduce the number of transitions between charging and discharging states and prolong the life of energy storage. In the pre-month optimization, a predicted monthly demand defense value is determined. In the intra-day rolling optimization, a subsection optimization model for daily operation of energy storage and a renewal model for monthly demand defense value are constructed. The daily load data and monthly demand defense value are updated in real time, and the rolling optimization is carried out to continuously correct the impact of load forecasting error. Finally, a large industrial user is simulated to verify the validity of the model.

      • SUN Yuwei, WU Chengjie, FU Chao, ZHANG Shuai, GAO Zhen

        Available online:October 18, 2019  DOI: 10.7500/AEPS20190513001

        Abstract:Power electronic transformers (PETs) are the key equipment in AC/DC hybrid distribution network. In order to improve the operation efficiency of cascaded PET under the condition of light-load, this paper proposes an efficiency optimization strategy based on active unbalanced power control, which utilizes the unbalanced characteristics of hybrid pulse width modulation (HPWM) technology. By analyzing the power losses of both cascaded H-bridge converter with HPWM and isolated bidirectional DC/DC converter, the operation efficiency model of cascaded PET is established. Based on the efficiency model, the feasibility for improving the overall efficiency of PET through unbalanced power distribution of each module is analyzed. The power stable operation range for each unit with HPWM is derived, and the active unbalanced power control strategy suitable for system efficiency optimization under the condition of light-load is proposed. Finally, the validation of the proposed strategy in comparison with the traditional power balanced control is confirmed by experiments, and the results show that the proposed unbalanced power control can reduce the power loss under the condition of light-load and improve the overall efficiency of PET.

      • ZHANG Xueyin, XU Yonghai, XU Shaobo, XIAO Xiangning

        Available online:September 04, 2019  DOI: 10.7500/AEPS20190328001

        Abstract:Medium-voltage multilevel converters usually adopt a modular structure. They can be used in AC/DC distribution networks. As a result of the relatively low voltage in distribution networks, the number of converter sub-modules is small. Therefore, carrier phase shift pulse width modulation (CPS-PWM) is widely used to increase the equivalent switching frequency. The modeling of CPS-PWM is one of the fundamentals of converter system modeling. The modulation stage is nonlinear, and thus, only the fundamental frequency component is usually considered. The existing fundamental approximation model of CPS-PWM is based on equivalent switching frequency, hence the low time delay and large errors when asymmetric regular sampling is adopted. In this work, the following three forms of fundamental approximation models of CPS-PWM are established: zero order holder (ZOH) delay approximation, ZOH no approximation, and delay Padé approximation. These models are developed by combining the outputs of sub-models on the basis of a sub-module. The proposed models more accurately reflect the frequency characteristics of CPS-PWM than the traditional one. A simulation study verifies the correctness of the theoretical analysis.

      • MI Yang, SONG Genxin, SONG Yuanyuan, YUAN Minghan, FU Yang, WANG Chengshan

        Available online:September 03, 2019  DOI: 10.7500/AEPS20190108003

        Abstract:The AC/DC hybrid multi-microgrids consists of multiple AC and DC sub-microgrid, and its stable operation depends on reasonable power management. How to play the autonomous feature of sub-microgrid and realize the power interaction between sub-microgrids is one of the key issues for the power management of AC/DC hybrid multi-microgrids. A multi-level power management strategy is proposed for the islanded AC/DC hybrid multi-microgrids. This management strategy consists of two parts: multi-level power allocation control and multi-level power interaction management. Reasonable allocation of power is achieved through power autonomous level, power interaction level, and power balance level. Considering the normal communication and communication failure, the multi-level power interaction management strategy is designed to ensure the power quality of the islanded AC/DC hybrid multi-microgrids and to reduce the unnecessary power interaction loss. The multi-level power interaction management strategy only exchanges data at the event triggering time, which reduces the amount of system information exchange and reduces the system requirements for the communication network. And the results of MATLAB/SIMULINK proved that the proposed control strategy is correct and feasible.

      • YANG Jingxu, YI Yingqi, ZHANG Yongjun, MO Yifu, HUANG Tingcheng, XIE Xiaoyu

        Available online:August 30, 2019  DOI: 10.7500/AEPS20190303007

        Abstract:Aiming at the analysis of operation risk of the distribution network caused by electric vehicle to grid, the indicator of loss severity with amplification factor is proposed, and the distribution entropy is used to measure the risk caused by the uncertainty of the distribution of the state variables of the distribution network. Weighting the distribution entropy using loss severity, the weighted distribution entropy (WDE) is established, based on which the voltage risk index and the load-flow risk index are established. The weighted sum of WDE is calculated according to the component importance, so as to evaluate the voltage risk and the load-flow risk of the network. Taking into account both types of risks, a comprehensive set of indexes is constructed to evaluate the operation risk of distribution networks. Finally, simulation studies are conducted on an improved IEEE 33-node distribution system with wind power and photovoltaic accessed, and the superiority of WDE over traditional risk indicators and the rationality of the comprehensive index are analyzed by dynamic probabilistic power flow simulation. In addition, the variation of the operational risk with the access location and capacity of electric vehicle load are studied. By the simulation studies, the effectiveness of the indicators and models proposed in this paper is verified.

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      • ZHU Yongqiang, ZHANG Quan, LIU Kang, WANG Zhi, WANG Fuyuan

        Available online:August 27, 2019  DOI: 10.7500/AEPS20190227008

        Abstract:In order to solve the power fluctuation caused by the change of micro-sources output, loads and power of energy storage devices in hybrid AC/DC microgrid, a segmented coordination control strategy for hybrid microgrid is proposed in this paper. Aiming at the hybrid microgrid in islanded state, the typical topology of the hybrid microgrid and the power relations under different operation modes are analyzed. The characteristic quantity which can represents the whole operation state of hybrid microgrid are obtained by standardization method. According to the variation of the characteristic quantity, the control strategy is divided into segments. Then the working principle of each section control is analyzed in detail and the coordinated control of the converters in different control segments are studied. Aiming at the possible power oscillation and frequent switching of ILC operation modes, the action criterion is compensated. Finally, a simulation model is established in PSCAD/EMTDC. The simulation results show that all converters can respond quickly under different operating conditions to ensure the stable operation of the system.

      • YUAN Hongtao, WEI Gang, ZHANG He, LUO Zhigang, HU Jue

        Available online:August 27, 2019  DOI: 10.7500/AEPS20190509008

        Abstract:This paper proposes an optimal scheduling model capable of considering comprehensively electric vehicle charging-swapping-storage integrated station and active distribution network. According to fast-charging users’ behavior characteristics and speed-flow practical model of city roads, battery fast charging station model and battery swapping station model are established respectively, which combined the cascade energy storage system as the integrated station model. In the active distribution network integrated with wind turbines, photovoltaics, micro-turbines and the integrated station, the optimal scheduling model is established, and the model is proposed to solve the problem via being transformed into a mixed integer second-order cone model. The multi-time scale optimization scheduling strategy based on model predictive control is used to realize day-ahead scheduling, intra-day rolling scheduling and real-time feedback correction, which reduces the impact of distributed generation and load prediction errors on distribution network operation. Taking the actual road conditions of a city"s bus lines as example, it is verified that the optimal scheduling strategy proposed in this paper has advantages of meeting the charging load demand of electric vehicles, suppressing power fluctuation and reducing ADN daily total operation cost.

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      • LI Guang, XUE Yongduan, YANG Fan, XU Bingyin

        Available online:August 20, 2019  DOI: 10.7500/AEPS20190127009

        Abstract:The physical simulation of the distribution network is receiving more and more attention. The transmission line often adopts the Π-shaped equivalent circuit chain network simulation. How to construct the transmission line model economically and effectively is very important. This paper has given the input impedance expressions of the lossless Π-shaped circuit chain network at different cascade numbers and clarified the difference in phase-frequency characteristics between the chain network and the lossless uniform transmission line. The amplitude-frequency error of the characteristic impedance between the Π-shaped circuit chain network and the lossless uniform transmission line is analyzed. It is found that when the operating frequency approaches or exceeds the upper limit frequency, with which the Π-shaped circuit chain network simulate the lossless uniform transmission line, the two are essentially different. Besides, the ratio between any frequency and the upper limit frequency is only related to the characteristic impedance error. The ratio of any frequency to the upper limit frequency is only related to the characteristic impedance error. In the chain network, each Π-shaped circuit is premised on working within its first resonant frequency, so that the reasonable error range of the characteristic impedance can be determined. Furthermore, the reasonable number of cascades suitable for Π-shaped circuit chain network of the distribution network can also be obtained. Through the calculation and simulation of typical transmission line parameters, the method is verified to be reasonable and effective.

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      • ZHAO Chengyong, LI Shuai, ZHANG Jiyuan, LI Jialong, XU Jianzhong

        Available online:July 31, 2019  DOI: 10.7500/AEPS20190128005

        Abstract:With the development of HVDC transmission technology, the isolation of DC faults is becoming increasingly important. As the most effective solution, hybrid HVDC circuit breaker is not mature enough, which restricted its engineering application. Accordingly, this paper proposes a low-cost DC fault isolation scheme suitable for HVDC grid. In this scheme, the traditional half-bridge MMC is partially innovated to have the ability of auxiliary breaking operation. With the effect of the MMC auxiliary breaking operation at both ends of the fault line, the DC fault current can be easily interrupted and isolated by low-cost circuit breaker unit installed in the DC transmission line. The equivalent circuit under the fault isolation process is analyzed, and the fault isolation sequences are designed. Furthermore, the devices usage comparative analysis among three schemes is performed. Finally, a four-terminal bipolar HVDC grid test model is built in PSCAD/EMTDC, in addition, an MMC prototype with proposed scheme is also developed. The simulation and experimental results validate the effectiveness of the proposed scheme.

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      Display Method: |

      Volume 44,2020 Issue 3

        >Views
      • CAO Wei, ZHANG Tian, FU Yesheng, YAO Yingbei, CHEN Siyuan

        2020,44(3):1-10, DOI: 10.7500/AEPS20190429015

        Abstract:With the increase of non-synchronous generators such as renewable energy and high voltage direct current transmission system, the inertia of power system has been reduced, which in turn leads significant changes to frequency characteristics of power system. Synchronous condensers as one type of synchronous machines has inertial responses, which provides short-time frequency support for the system. Firstly, the principle of inertial response of synchronous condensers and its interaction with synchronous generators are introduced. Secondly, taking the application of inertial response for synchronous condenser as entry point, the worldwide work on improving the inertial responses and frequency characteristics of power system is sorted out, including the synchronous inertia level of power system, the measurements to improve the synchronous inertia, the effect of synchronous inertia on frequency response in power system and so on. Finally, combined with the worldwide research experiences, the necessity for East China Power Grid to apply synchronous condensers to enhance the frequency support of power system is analyzed, and relevant suggestions are put forward.

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      • >Energy Transformation and Power Support
      • CHEN Zexing, LIN Kaidong, ZHANG Yongjun, CHEN Boda, SU Jieying

        2020,44(3):11-23, DOI: 10.7500/AEPS20190613001

        Abstract:Integrated electricity-gas system (IEGS) based on bi-directional coupling of gas turbine and power to gas (P2G) is an important carrier to realize accommodation of high-proportion renewable energy and improve terminal energy utilization efficiency. Firstly, based on the comparison of transmission characteristics of power system and natural gas system, the connotation, characteristics and advantages of IEGS are described. Secondly, the technical principle and modeling method of P2G in IEGS are introduced. Furthermore, the research progress of relevant technology is emphatically summarized from two dimensions: solution of IEGS energy flow model and optimization of IEGS operation scheduling. In terms of research on optimal operation scheduling, it is discussed from five aspects, including basic scheduling model and consideration of system randomness, energy flow difference and market operation mechanism and non-linear processing method of model. Finally, the prospect of future research on IEGS modeling and operation optimization are proposed.

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      • NIU Qifan, WU Peng, ZHANG Jing, CHENG Haozhong, ZENG Yi, YANG Jianlin

        2020,44(3):24-31, DOI: 10.7500/AEPS20190425002

        Abstract:The electricity-natural gas coupling system consisting of gas generation units and power to gas (P2G) facilities improves the interaction of different energy systems. In order to realize the safe and economic operation of the coupling system during planning year, an optimal planning method for electricity-gas coupling system considering P2G is proposed, which aims at minimizing the sum of annual investment cost and annual operation cost. This optimization method can obtain the construction state of gas generation units, P2G plants, power lines, gas pipelines and optimal output of typical daily gas generation units and P2G plants in the planning year. Then, based on the proposed method, 7-node natural gas and 9-node power system can be modeled and calculated in different scenarios. Finally, the results of immune algorithm show that the reasonable location planning for P2G plants can reduce the construction cost of natural gas network pipeline, and the output adjustment of gas generation units and P2G plants can reduce the operation cost of the system.

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      • >Basic Research
      • SUN Li, CHEN Wu, JIANG Xiaojian, PAN Pengpeng, ZHANG Ke

        2020,44(3):32-39, DOI: 10.7500/AEPS20190404005

        Abstract:Multi-port energy router is an effective topology structure of integrating photovoltaic, energy storage and charging pile of electric vehicle. When energy routing is performed at different ports, the energy router involves multiple operation modes. Therefore, seamless mode transition is a major difficulty. In the Energy Internet framework, hierarchical control of multi-port energy router enables coordinated operation to achieve seamless mode transition in power grid dispatching, grid-connected/off-grid conditions or in the condition that electric vehicle is integrated or cut off. The control layer of micro-network adopts centralized control to maintain the overall energy balance of the system with various operation modes, which interacts with the upper-level scheduling layer to respond to scheduling, communicates with the lower-level local control layer by sampling the state information of each port, and calculates the references current of energy storage and the charging pile. In the local control layer, ports of photovoltaic and voltage source converter adopt distributed control to reduce the communication bandwidth. Ports of energy storage and the charging pile adopt the proposed new droop control strategy based on current tracking to accurately transmit the required power and control the voltage stability of DC bus. Finally, the effectiveness of the proposed unified coordinated control strategy is verified by MATLAB simulation.

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      • HU Liping, SUN Yingyun, WANG Chunfei, PU Tianjiao, CHEN Naishi, SUN Ke

        2020,44(3):40-48, DOI: 10.7500/AEPS20190319005

        Abstract:For the complexity of operation mode of the power electronic transformer (PET) ports and their multiple combinations in hybrid AC/DC grid composed of several PETs, an optimal combination method of operation strategy for PETs based on generalized AC/DC droop control (GADDC) is proposed, the objective of which is to fully utilize the renewable energy while maintaining the stability operation of power system. The switching between different control modes of PET ports could be approximated by adjusting the coefficients of GADDC, which avoids importing integer variables in the non-linear programming model, thus effectively reducing the complexity of the proposed model. Based on this, a robust combined optimization model of PET operation strategy considering the uncertainty of renewable energy is established. Furthermore, a bi-level optimization method is adopted to solve the proposed model. Simulation results verify the effectiveness and feasibility of the proposed method.

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      • WEI Chun, XU Jianqi, LU Haiqiang, WANG Jinyue, ZHANG Youbing

        2020,44(3):49-55, DOI: 10.7500/AEPS20190120006

        Abstract:The control objective of DC microgrid is to ensure the accuracy of current distribution and reduce the deviation of DC bus voltage, so as to maintain the power balance of the system. These two control objectives cannot be achieved simultaneously by the traditional droop control. By using the distributed secondary control framework, this paper proposes an improved control strategy for DC microgrid based on discrete time interaction, including continuous-voltage control and discrete-current control, which can ensure the accuracy of current distribution and reduce the voltage deviation of DC bus simultaneously. Different from other proposed control methods, the proposed method in this paper only needs to sample the average current information at discrete times, which reduces the communication burden. The system model is built in MATLAB/Simulink to verify the effectiveness of the proposed control strategy.

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      • YANG Jing, WANG Tong, BI Jingtian, LI Yan

        2020,44(3):56-65, DOI: 10.7500/AEPS20190128009

        Abstract:The fluctuation of wind power may lead to the change of operation point in power system. In order to effectively improve the adaptability of subsynchronous oscillation damping control, a subsynchronous oscillation robust damping controller is designed by using the additional control method of direct-drive wind turbines. Firstly, based on the linearized state space model, the mixed H 2/H control with regional pole placement is used to suppress the power system subsynchronous oscillation caused by random disturbance. The convex polytope model is constructed by using different operation points as the vertices of the convex polytope to adapt to the wide variation of system operation points caused by wind power output fluctuations and improve the robustness of the controller. Secondly, a linear matrix inequality is applied to solve the state feedback matrix and design a subsynchronous oscillation robust damping controller. Finally, a four-machine two-area system with two direct-drive wind turbines is used as the test system for time domain simulation. The simulation results show that the robust damping controller based on convex polytope can provide sufficient damping for the subsynchronous oscillation modes, and the controller also has good control effect when the outputs of wind power change over a wide range.

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      • LIU Haobang, MA Hui, XIONG Zhizhi

        2020,44(3):66-73, DOI: 10.7500/AEPS20190401006

        Abstract:With the increasing penetration rate of renewable energy in power system, the system ability of supporting frequency is getting worse and worse. Configuring virtual inertia for power system is an effective way to solve this problem. To effectively allocate the virtual inertia, the Voronoi diagram interpolation method is proposed to optimize the virtual inertia distribution. The mathematical model of virtual inertia in power system is established. The stability of the system is judged by Lyapunov direct method and the 2-norm of the decision matrix is used as comprehensive evaluation performance indicators. The stability of the system frequency is analyzed when multiple influence factors interact. The Voronoi diagram and center of gravity interpolation method is used to find the optimal solution of the inertia. The optimization results are verified by simulation. Compared with other traditional methods, simulation results show that the virtual inertia is configured based on the method. The result is more accurate and the calculation speed is faster, and it could use virtual inertia more effectively to improve system frequency stability.

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      • XU Chengsi, DONG Shufeng, WU Jincheng, HAN Rongjie, SHOU Ting, LI Jianbin

        2020,44(3):74-82, DOI: 10.7500/AEPS20190520010

        Abstract:In order to scientifically determine the number and location of energy stations and the distribution of energy supply pipelines in regional integrated energy system, the planning method of energy stations and pipelines considering topological characteristics of regional integrated energy system is proposed. Firstly, the topological characteristics of regional integrated energy system are summarized. According to the urban planning scheme and geographic information system, the optional energy station sites and pipeline channels are obtained. Secondly, a topological description model of energy system is established based on energy flow balance constraints and heating network characteristics. To minimize the cost of initial construction and later operation, the layout planning model of energy station and energy supply pipeline is established, and orthogonal polynomial approximation is used to simplify the optimization model. The simulation results show that the proposed method could obtain a more economical planning scheme.

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      • ZHANG Ruiqi, DONG Xiaoming, WANG Mengxia, YANG Ming, WANG Yong

        2020,44(3):83-88, DOI: 10.7500/AEPS20190619007

        Abstract:Taking long-distance large-scale wind farms connected to the grid as the research background, and considering the synchronization effect of environmental factors on the current-carrying law of the transmission line and its mechanical performance degradation, electro-thermal coordination theory and line aging failure model are organically combined. Based on the electro-thermal coupling and life-cycle cost, the maximum allowable temperature assessment model for renewable transmission lines is proposed, which provides an evaluation basis for the renewable energy consumption capacity and operation performance of the grid. The model continuously processes the environmental variable values according to various setting schemes of maximum allowable temperature, and simulates annual variations of electrical and physical state parameters of the line based on the thermal inertia equation of the overhead conductor.Then, the duration of each temperature interval is calculated and the life-cycle performance of line is predicted based on the aging failure model of transmission line. The life-cycle cost of the line can be obtained according to the failure rate model, the annual average profit of investment for transmission line and analytic function expression of the maximum allowable temperature for transmission line on the premise that the access income of unit wind power is fixed, thereby achieving the goal of maximizing the annual average profit. Finally, effectiveness of the proposed model and its effect on improving the economic and safety of the system operation are verified by the actual case study.

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      • LIU Hong, ZHENG Nan, GE Shaoyun, XU Zhengyang, GUO Li

        2020,44(3):89-97, DOI: 10.7500/AEPS20190312010

        Abstract:In the coordinated planning process of distributed generator (DG) and network structure of active distribution system, it is difficult to consider their interaction in the operation process simutaneously. To solve this problem, a mathematical model and solving algorithm for multi-agent balance of interest considering planning and operation alternative optimization are proposed. Firstly, considering demand response and operation strategy, a tri-level optimization framework and mathematical model based on the optimal cost-effectiveness of distribution network and DG are established. Secondly, the network simplification method based on topological equivalence principle is presented. Based on the in-depth analysis of the topological structure variation in the network structure generation process, a rapid generation strategy for link and loop network based on broken circle method is proposed. Then an encoding/decoding scheme of particle swarm optimization is developed. Thirdly, based on the load characteristics and demand response willingness of customers, an optimization method and operation strategy for dynamic time-of-use price are proposed, and coordinated planning solution process of the source and network considering the operation optimization is presented. Finally, the efficiency and practicability of the method are demonstrated on a practical system.

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      • ZHAO Hongshan, YAN Xihui, DAI Xiang, WEN Haiyan

        2020,44(3):98-104, DOI: 10.7500/AEPS20190516005

        Abstract:Domestic electric water heater (EWH) has great potential in the demand response (DR) market because its power consumption is highly correlated with daily load patterns and it accounts for a high proportion of the household consumption. Recognizing load patterns of residential EWHs and quantifying their flexibility in DR help grid operators develop reasonable regulatory strategies. Firstly, probability statistic models are established for load patterns (the start time, the end time and the duration of the power event) of residential EWH with different time types. Secondly, a training-less non-intrusive load extracting (NILE) algorithm based on load signatures and power block extremum is proposed, which can automatically separate EWH loads with different rated power levels. Finally, an incentive price-based DR model is established to optimize load patterns of EWH, and flexibility of EWH is quantified based on changes in their usage behavior before and after optimization. Furthermore, the validity of the proposed algorithm is verified with an actual dataset, and the flexibility of EWH participating DR in different conditions is quantified based on the separated load data.

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      • JIANG Tingyu, JU Ping, WANG Chong

        2020,44(3):105-113, DOI: 10.7500/AEPS20190325008

        Abstract:Large-scale aggregated air-conditioning load can change its aggregated power through demand response, which plays an important role in peak shaving, balancing fluctuations of renewable energy and providing auxiliary service. For the dispatching of power grid, it has a practical meaning to establish a model to describe the characteristics of aggregated air-conditioning loads. Compared with the extensive researches on independent model for air-conditioning loads, there are few researches on aggregated model for air-conditioning loads which requires accurate parameters in modeling. Based on the method of adjusting the temperature setting of air-conditioning, this paper proposes a simplified aggregated power model for air-conditioning loads considering outdoor environment temperature variations and the stochastic adjustment behaviors of the consumers. In addition, the proposed model is simplified based on the state queuing model, which can effectively reduce computation burden and real-time communication pressure during dispatching. The accuracy and feasibility of the proposed model are verified through simulation analysis.

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      • WANG Yi, GU Yi, DING Zhuang, LI Songnong, WAN Yi, HU Xiaorui

        2020,44(3):114-121, DOI: 10.7500/AEPS20190424013

        Abstract:A charging demand forecasting method of electric vehicle based on empirical mode decomposition-fuzzy entropy and ensemble learning is proposed. This method decomposes the time series of charging demand for electric vehicle into relatively simple components by empirical mode decomposition. In order to avoid the cumbersome calculation and error accumulation caused by excessive components, firstly, the complexity of each component is calculated by using fuzzy entropy. The components are superimposed and combined to obtain a series of sub-sequences to reduce the number of components. Secondly, long short-term memory (LSTM) neural networks and supported vector regression (SVR) are used as the base learner for prediction of sub-sequences with different frequencies. Finally, the prediction result of base learner, the weather data and time series data of the pre-decomposed charging demand are combined to form the feature set by the Stacking integrated learning strategy. Final forecasting results are obtained through a fully connected neural network. Single-step and multi-step prediction experiments are carried out based on real data of charging demand for electric vehicle in a certain area of a certain city in Southwest China, and the comparison with other algorithms is made, which shows the reliability of the proposed method..

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      • DING Renjie, SHEN Zhongting

        2020,44(3):122-131, DOI: 10.7500/AEPS20190321005

        Abstract:The paper proposes a mode identification method for low frequency oscillations in power systems based on exact mode order-exponentially damped sinusoids neural network (EMO-EDSNN). Firstly, the mode order is estimated via singular value decomposition. An EMO method is employed to solve the key problem of order determination. It comprehensively considers the variation laws of singular values change and the values themselves, thus overcoming shortages of artificial thresholds and enhancing the accuracy of order determination. Secondly, the EDSNN is constructed to translate the parameter estimation into an optimization problem. After training the neural network via the self-adaptive Levenberg-Marquardt algorithm aiming for a minimum square error between output and real signals, all the mode parameters can be obtained simultaneously. Finally, simulations of numerical signals, EPRI-36 system and actual signals are carried out. The results show that the proposed method can identify the mode parameters in an accurate and reliable manner.

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      • LI Bin, JIA Bincheng, SUN Yi, QI Bing, JING Dongsheng, XI Peifeng

        2020,44(3):132-138, DOI: 10.7500/AEPS20190428002

        Abstract:Due to the particularity of power industry, the reliability of power communication network carrying its business transmission has been paid more and more attention. With the continuous improvement of the communication network structrue, the network gradually presents the characteristics of vertical layering, which makes cross-layer joint protection possible. A cross-layer protection based on network coding (CLPBNC) strategy is proposed for power communication network. In IP layer, network coding is used to protect links. In optical transmission network, preconfigured cycle (P-cycle) is used to recover link failure. And conditions of cross-layer joint protection are studied to improve protection efficiency. The simulation results show that CLPBNC can effectively reduce the redundancy of protection, improve the efficiency of protection and optimize the overall performance of the network.

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      • SHAN Hua, WANG Qian, YUAN Chao, ZHANG Cunjian, MEI Rui, LUO Zhao

        2020,44(3):139-146, DOI: 10.7500/AEPS20190123009

        Abstract:Pumped-storage power station has the auxiliary service function of phase modulation, which provides reliable supporting for stable operation of power grid. Firstly, in view of the current situation that no compensation analysis is made for phase modulation service of pumped-storage power station in electricity market environment, this paper designs a compensation mechanism for the phase modulation service with “two-part system” price of reactive power in order to objectively measure the quality of the phase modulation service of pumped-storage power station and balance the benefits between power grid enterprise and pumped-storage power station. Secondly, based on Stackelberg game theory, a compensation model of pumped-storage power station is constructed and the existence and uniqueness of Nash equilibrium solution are proved. Finally, simulation analysis of Liyang pumped-storage power station in Jiangsu Province of China is carried out to obtain the benefits of both sides of the game with the equilibrium solution. The example shows that the reactive power compensation cost of power grid enterprise is related to the type of phase modulation service. Through the draft of reactive power price, the benefits of both pumped-storage power station and power grid enterprise can be increased, and the pumped-storage power station can be encouraged to provide the phase modulation service. Also, suggestions on reactive power bidding and compensation mechanism of the phase modulation are given.

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      • >Application Research
      • ZHANG Wen, SHENG Wanxing, DU Songhuai, JIA Dongli, KANG Tianyuan

        2020,44(3):147-153, DOI: 10.7500/AEPS20190520009

        Abstract:Accurate faults prediction and potential risk scanning of distribution network through flexible analysis and application of multi-source heterogeneous data are meaningful to realize efficient and accurate operation analysis decision of distribution network. The overall structure and function design of a distribution network operation analysis system based on mass data are introduced, and the functions and analysis results of each module are demonstrated by an application example. The system integrates data such as geographic information system (GIS), marketing business application and distribution automation. By using improved machine learning algorithm and weak point identification method, the functions of data correlation analysis, fault risk level prediction and weak point identification of target distribution network are extended. It is beneficial for relevant departments to propose corresponding technologies and management methods to carry out the operation and maintenance of distribution network, improve the scientific and practicality of the existing distribution network analysis system, and ultimately lay the foundation for the informatization, intellectualization and leanization of distribution network operation analysis.

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      • NIE Zheng, ZHANG Jianmin, FU Huawei

        2020,44(3):154-161, DOI: 10.7500/AEPS20190524005

        Abstract:The low-voltage distribution network is the most core area of the application of electric power Internet of Things (EPIoT). It is necessary to extend the smart low-voltage distribution network to EPIoT in nature. Present data acquisition and automation system for low-voltage distribution network needs to be developed into the cloud-edge node-edge device system architecture. As a core edge node, distribution transformer terminal unit (TTU) should have a quick iteration capability to realize the edged fusion and cloud-edge coordination of various old/new businesses. To meet such technique requirements, the key technologies such as container technology to support edge node are analyzed firstly. Secondly, the key implementation technologies to make TTU becoming a containerized edge node are proposed including hardware platform, software architecture, container deployment and interaction, container management, coordination between cloud and edge. Finally, by adding a new low-voltage circuit terminal unit (CTU), the application scenario for TTU is designed and its necessity to become a containerized edge node is demonstrated.

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      • SU Yunguang, LUO Jun, XIONG Hao, FAN Qing, WU Haiwei, CHEN Lianjie

        2020,44(3):162-166, DOI: 10.7500/AEPS20190404002

        Abstract:Because there are many types of equipment in the substation, the wiring is complex and each place has its own wiring graph drawing habits, it is difficult to automatically generate high-availability substation wiring graphs that meet users’ drawing habits. A topological analysis method based on the graphic description specification for electric power system CIM/G is proposed, which is used to identify and extract the features of the inventory graphs, to establish the graphic feature database, and to realize the automatic generation of the substation wiring graph by using the graphic features. This paper presents a case of generating a 220 kV substation graph in Lianyungang, Jiangsu Province of China, and verifies the correctness and effectiveness of the automatic generation of substation wiring graph based on the topological analysis of inventory graphs.

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      • GAO Yinghan, TANG Fen, LIU Jingdou, XIAO Qi, WU Xuezhi, LI Xiangjun

        2020,44(3):167-175, DOI: 10.7500/AEPS20190330002

        Abstract:The grid-connected control based on inductor current on the side of converter in synchronous rotating coordinate system is widely applied in the grid-connected converter with LCL-filter. However, the axe-cross-coupling exist in the dq models of LCL filter and digital delay, which constrains the grid-connected performance and becomes worse as the switching frequency decreases. To address this issue, based on the complex vector modeling of grid-connected converter with LCL-filter, this paper analyzes the coupling characteristics of the grid-connected converter and the conventional decoupling scheme. Aiming at the shortcomings of the existing control strategies, this paper proposes an improved control strategy of the grid-connected converter with LCL-filter based on phase compensation and virtual impedance optimization. Then, the effect of virtual impedance on system coupling and system damping characteristics is analyzed in detail through the zero-pole plots. And the method for determining optimization values of three parameters are given. Finally, the simulation and experimental results show that the proposed strategy can achieve independent control of system coupling degree and damping characteristics, while effectively realize decoupling and improve system dynamic performance.

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      • XU Chenhua, WU Jiansong, LIU Bin, CHEN Yanming, LU Yimin, LYU Zhilin

        2020,44(3):176-184, DOI: 10.7500/AEPS20190512006

        Abstract:The derivation of the traditional modulation strategy for unipolar and bipolar single-phase inverters is based on the assumption that the DC bus voltage is an ideal constant DC parameter. However, due to the DC/AC power coupling, the DC bus voltage of the single-phase inverter contains a large amount of ripple component of double AC voltage frequency in the practical single-phase inverter. With the traditional modulation strategy, the second-order ripple component causes the increase of the third-order harmonic on the AC side, and impacts the power quality of AC output voltage. By means of the double Fourier transform method, the harmonic characteristics of output voltage are theoretically evaluated. Then, this paper proposes a harmonic reduction modulation strategy of single-phase inverter with a high second-order ripple rate of voltage on the DC side. Based on the third-order generalized integrator, the second-order ripple component in the DC bus voltage is extracted by the enhanced phase-locked loop (PLL). By injecting the opposite second-order components into the modulation coefficient, the third harmonic and the total harmonic distortion (THD) of the output voltage have been reduced. Finally, the rationality and feasibility of the active modulation strategy are verified by experiments.

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      • SUN Wei, YU Hao, YANG Jianping, GAO Bo, WANG Yu, QIN Shaorui

        2020,44(3):185-193, DOI: 10.7500/AEPS20190124005

        Abstract:In the data acquisition and communication applications of smart grid based on wireless sensor network (WSN) , communication reliability is a key technical indicator of WSN. Increasing the transmit power improves the signal strength and reliability of the communication, but simultaneously degrades the mutual interference between the nodes. To solve this contradiction, this paper studies the optimization of WSN transmit power in the smart grid based on the adaptive model predictive control method. The main factors affecting the signal-to-noise ratio (SNR) of wireless communication in the smart grid are analyzed based on the wireless communication link path loss model, and the system state space model is constructed. By real-time estimation of the lower bound of stochastic fluctuation confidence interval of SNR, the compensation is performed and the algorithm based on the model predictive control is used to optimize the transmit power of the node. Finally, the proposed algorithm is compared with the adaptive transmission power control (ATPC) and potential feedback control (PFC) algorithms by simulation software, and the algorithm is tested by WSN hardware platform. The adaptive model predictive control algorithm can reduce the mutual interference between nodes caused by too high transmit power under the condition of ensuring the reliability of smart grid wireless communication.

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      • ZHANG Peng, WANG Wei, XU Bingyin, JIA Mingna, LIANG Dong, ZHANG Shengpeng

        2020,44(3):194-200, DOI: 10.7500/AEPS20190624006

        Abstract:The energy-gaining power supply of current transformer has the heating problem when the bus current is high, which affects the service life of power supply. For this reason, this paper proposes a design method of the energy-gaining power supply for the current transformer based on self-adaptive power output control. Based on the analysis of the power acquiring principle of current transformer, the load equivalent model of energy-gaining coil of the current transformer is established, and the relationship between the output power of the coil and the bus current is derived. By controlling the on-off state of the bidirectional thyristor, the purpose of controlling the power output of energy-gaining coil is achieved, and it is ensured that the power supply does not heat up at a large current. An implementation form of self-adaptive power output control circuit is given. By establishing its equivalent model, the relationship between the conduction angle and the bus current is derived. Finally, the experiment shows that the power prototype made according to the proposed design method can work in a low heat consumption state in a wide current range, which verifies the feasibility of the proposed method.

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      • HUANG Xinbo, ZHANG Xiaoling, ZHANG Ye, YANG Luya, LIU Cheng, LI Wenjing

        2020,44(3):201-210, DOI: 10.7500/AEPS20190122004

        Abstract:The transmission line plays an important part in power transmission task, so it is of great significance to identify its defects for the maintenance, and the severe power accidents can be avoided or decreased. For the background of images captured by unmanned aerial vehicle is very complex and difficult to be detected, a radial basis probabilistic neural network based fault location identification method for transmission lines is proposed. Firstly, the weighted color difference method, maximum interclass variance method and morphological filtering are sequentially adopted to realize the accurate segmentation of transmission lines in complicated background. Secondly, the segmented line area is equally divided into 10 line sub-images, 40 texture enhancement sub-images at 8 angles and 5 dimensions of transmission lines are obtained by Gabor filter, and the roughness, contrast and orientation of each sub-image are also extracted. By the feature variance, 10 strong texture features are selected and adopted as the input parameters to the radial basis probabilistic neural network for the defect identification of transmission line. The results show that both the rapid segmentation of transmission lines and the accurate identification of the defects based on the images in the complex background can be achieved by the proposed method, which provides a new idea for the operation state detection of transmission line in unmanned aerial vehicle inspection.

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      • >Egineering Application
      • SUO Zhiwen, LI Hui, JIANG Weiyong, LIU Zengxun, XU Decao

        2020,44(3):211-219, DOI: 10.7500/AEPS20190823003

        Abstract:At present, the traditional control mode is commonly used in China’s running HVDC projects, which may lead to frequent action of DC discrete voltage regulation equipment with a fluctuation of DC power and voltage, and directly affect the HVDC project operation reliability. In view of the technical requirement for reducing the action frequency of DC discrete voltage regulating equipment, this paper firstly analyzes the action influencing factors of discrete voltage regulation equipment. Based on this, the HVDC traditional constant extinction angle and constant DC voltage control modes are respectively improved considering the coordination of tap-changer, AC filter and dynamic reactive compensation. And DC operating voltage varies with DC power within selected power range is proposed. Then the impact of the proposed strategy is analyzed and the corresponding optimization suggestions are given. Finally, the above analysis is verified based on DC main loop calculation and electromagnetic transient simulation. The results show that the proposed strategy can effectively reduce the action frequency of DC discrete voltage regulating equipment.

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      • XIAO Bai, LI Panpan, JIANG Zhuo, SHI Yonggang, JIAO Mingxi, WANG Yao

        2020,44(3):220-228, DOI: 10.7500/AEPS20190823002

        Abstract:Aiming at the problem of how to realize the efficient transformation of rural electric power grid through precise investment, a lean transformation method for rural electric power grid is put forward based on cascaded combination scoring. Firstly, the main problems existing in the current rural electric power grid are sorted out, and the corresponding evaluation indices are defined. The calculation formulas for matching each evaluation index are given. The severity of each problem is graded, and the cascaded evaluation criteria for each evaluation index is set up. An evaluation index system is constructed, which can fully reflect the weak links of rural electric power grid and its severity. Secondly, according to the index value, the equipment that needs to be transformed is determined and taken as the evaluation object. According to the evaluation index evaluation criteria, the evaluation object is scored. The weight of each evaluation index is determined by criteria importance through intercriteria correlation (CRITIC) method, the comprehensive score of evaluation object is calculated and the cascaded combination score of the evaluation objects is then completed. Finally, the evaluation objects are arranged in the descending order according to the size of the comprehensive score and the top ranking equipment should be given priority to be reformed first. The example analysis proves the correctness and effectiveness of the method.

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      • >Survey
      • LIU Shengyuan, LIN Zhenzhi, LI Jincheng, ZHAO Yuxuan, ZHANG Bo, YANG Li

        2020,44(3):229-239, DOI: 10.7500/AEPS20190402008

        Abstract:The concept of situation awareness was first proposed in the fields of space and cyber security, and then involved in the field of power systems. In recent years, the global scholars have extensively discussed the application of situation awareness technologies in power systems. In this background, the real-time operation state identification, the operation trend prediction, and the situation visualization technologies of power systems are respectively mapped to the three elements of situation awareness defined by Endsley (i.e. “perception”, “comprehension”, and “prediction”). And the wide-area control and risk dispatching are mapped to the “decision action” in situation awareness. The event detection, event identification, risk prediction, situation visualization technology, wide-area control, and risk dispatching of power systems are reviewed and analyzed. The ideas of existing methods are described. Finally, the deficiencies of existing research on situation awareness of power transmission systems are pointed out, and the artificial intelligence and big data technologies are regarded as the future research direction to solve the issues in situation awareness of power systems.

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      Display Method: |
      • XIN Yaozhong, SHI Junjie, ZHOU Jingyang, GAO Zonghe, TAO Hongzhu, SHANG Xuewei, ZHAI Mingyu, GUO Jiancheng, YANG Shengchun, NAN Guilin, LIU Jinbo

        2015,39(1):2-8, DOI: 10.7500/AEPS20141008024

        Abstract:Firstly, the development history of power grid dispatching automation systems in China is reviewed. The architecture of smart grid dispatching and control systems is described. Then the main technical breakthroughs of smart grid dispatching and control systems are summarized, including improvement of the observability and controllability of ultra large power grids, the coordinated ability of control centers, the early warning ability of on-line dynamic security of ultra large power grids, the economic operation efficiency of ultra large power grids, the ability for power grids to accommodate new energy generation, and the ability of the control centers of power grids to withstand major natural calamities and group cyber-attacks. Finally, further research areas of smart grid dispatching and control systems are outlined.

      • WANG Xifan, WANG Biyang, WANG Xiuli, SHAO Chengcheng

        2014,38(17):4-13, DOI: 10.7500/AEPS20140324013

        Abstract:Offshore wind energy is a promising solution to the environment and energy crisis thanks to its excellent performance of production.It would be further developed with the support from low-carbon economy.This paper summarizes the configuration of offshore wind power systems and surveys their optimal planning methods.Methods of offshore wind farm siting,common topologies of collecting systems and different transmission schemes are reviewed,while reliability evaluation is discussed in detail.Based on this,modeling approaches and algorithms for optimal planning of offshore wind power systems are briefly treated.Finally,some suggestions for potential research directions of optimal planning of offshore wind power systems are made.

      • XUE Yusheng, LAI Yening

        2016,40(1):1-8, DOI: 10.7500/AEPS20151208005

        Abstract:The macro energy thinking which regards electricity as a hub between energy production and consumption, can promote “clean energy substitution” of the upstream primary energy and “electricity substitution” of the downstream end-use energy, in order to support the sustainable development of energy. Meanwhile the big data thinking regards various data resources as fundamental elements of production rather than simple process objects. The integration of these thinking will make the big data on power become the foundation of an extensively interconnected, openly interactive and highly intelligent macro energy system. Key elements of this integration include the acquirement, transmission and storage of wide-area power data with different timescales, the data from related domains, as well as the fast and in-depth knowledge extraction from the multi-source heterogeneous data and its applications. As the first part of a series of paper, this paper summarizes unique features of big data based on the deduction of the basic concept, data structures and essential characteristics of big data. For the comprehensive energy network, a knowledge extraction platform is constructed by integrating the causal data (based on mathematical models), the statistic data (with non-causal relationship) and the gambling data (of human participants). More case studies will be proposed in the subsequent paper, which will show the contributions of big data thinking to enhance the economy and reliability of macro energy systems. This work is supported by National Natural Science Foundation of China (No. 61533010), NSFC-EPSRC Collaborative Project (No. 513111025-2013), China-Thailand Cooperation Fund Project (No. 5151101161), and State Grid Corporation of China.

      • WEI Zhinong, YU Shuang, SUN Guoqiang, SUN Yonghui, WANG Dan

        2013,37(21):196-202, DOI: 10.7500/AEPS20130513006

        Abstract:The virtual power plant(VPP),which has received much attention of the developed countries in Europe,is an effective management form of grid connection of distributed energy resources as well as an important component part of the smart grid.In the past ten or more years,the European Union/European countries have carried out many research and pilot projects on VPP.These projects not only have different emphases,but also constitute an integral system.Focusing on VFCPP,Power Matcher VPP,FENIX,EDISON and WEB2ENERGY projects,a description is made of European VPP-related research projects prior to their summation.The major problems of VPP which still need to be addressed are proposed.

      • 程时杰

        2013,37(1):3-8, DOI: 10.7500/AEPS201209150

        Abstract:An analysis is made of the role energy storage technology will play in the development and reform of power systems.A comprehensive survey is made of such aspects as the basic principles,technical performance,development status,main problems,and key bottlenecks needing solution.Evaluation indices for large-scale application of energy storage technology are presented.On this basis,the development and application prospects of multiple energy storage technologies are analyzed and a roadmap is provided.

      • YU Yixin, LIU Yanli

        2015,39(2):1-5, DOI: 10.7500/AEPS20141204007

        Abstract:Barrier exists in every stage of developing a smart grid,from fundamental science and engineering technology research to development,demonstration and operation.Figuring out the critical barrier will be helpful to clarifying how to maximize smart grid's potential,thus providing comprehensive social and economic benefits to the nation.This paper identifies eleven key challenging issues of the smart grid and emphasizes that metrology and standardization are the priority important areas,interdisciplinary cooperative research is the inevitable choice for developing the smart grid,while legal framework and supervision,market design and management reform are the basic guarantees of successfully implementing the smart grid and obtaining the deserved benefits.

      • CHEN Xu, ZHANG Yongjun, HUANG Xiangmin

        2016,40(1):143-151, DOI: 10.7500/AEPS20150330005

        Abstract:In order to adapt to the access of high penetration and large-scale distributed generators (DGs), the active distribution network (ADN) has become the research trend of current and future smart grids. The influences of DG access, demand-side management and topology changes on the voltage distribution and voltage stability of distribution network in the AND background are reviewed. The reactive power and voltage control method of ADN are summarized from the perspective of centralized and decentralized control. According to an analysis of the current research status, some of the problems and shortcomings of research on reactive power and voltage control method of AND influenced by various factors are briefly treated. Some problems in research on the AND reactive power and voltage control method are pointed out. This work is supported by National Natural Science Foundation of China (No. 51377060).

      • ZHAO Junhua, DONG Zhaoyang, WEN Fushuan, XUE Yusheng

        2017,41(4):1-11, DOI: 10.7500/AEPS20160813002

        Abstract:The comprehensive energy system, which can coordinate multiple types of energy and be characterized by a deep integration of “cyber-physical-social” systems, is emerging. There is therefore an urgent need to conduct in-depth study on data science and big data mining for energy systems. This paper presents an initial discussion on data science and its applications in comprehensive energy systems. The fundamentals of data science, in particular the importance of the statistical learning theory and data quality, are discussed first. The new progresses in big data mining, such as deep learning, transfer learning and cross domain data fusion, are introduced then. Finally, a brief review is given on the applications of data mining techniques in energy systems; some research problems in energy system data mining, which require further attentions in future, are also discussed. This work is supported by National Basic Research Program of China(973 Program)(No. 2013CB228202), National Natural Science Foundation of China(No. 51477151)and Specialized Research Fund for the Doctoral Program of Higher Education of China(No. 20120101110112).

      • QIN Wenping, WANG Peng, HAN Xiaoqing, LIU Zhijuan

        2014,38(1):28-33, DOI: 10.7500/AEPS20130529009

        Abstract:Reactive power plays an important role in power system reliability as it is closely related to system voltage stability and voltage collapse.However,the reactive power related reliability issues are seldom emphasized in conventional power reliability evaluation.This paper studies the power system reliability from the perspective of active and reactive power,respectively.Active and reactive power inadequacy and the associated voltage perturbation due to system failure are considered in reliability evaluation of power systems.A three-stage load shedding technique for past contingencies are implemented to determine the influence of active and reactive power on system reliability and to find an optimal way to relieve network violation.

      • JU Ping, LIU Yongfei, XUE Yusheng, LI Hongyu, SUN Lixia, ZHOU Haiqiang

        2017,41(1):1-8, DOI: 10.7500/AEPS20160530011

        Abstract:Randomness exists extensively in nature, engineering and social systems, the power system not excepted. Randomness has gradually taken into consideration in power system analysis since the 1970s, with emphasis on analysis of steady-state random problems while research on power system dynamics is still based on the deterministic theory. In recent years, with increasing integration of typical sets of stochastic sources into power systems, such as the large-scale renewable power generation and electric vehicles, the influence of randomness on power system dynamics can no longer be neglected. For this reason, a research framework is proposed for stochastic dynamics of power system focusing on dynamic problems under the action of randomness, including stochastic dynamic modelling, stochastic dynamic responses, stochastic stability, stochastic dynamic security and stochastic optimum control of power system. Some suggestions are given for the research.

      • XIA Yan, LI Gengyin

        2017,41(13):22-29, DOI: 10.7500/AEPS20161123004

        Abstract:The establishment of distribution market needs to rely on the friendly interaction between various resources and power grid in the distribution network. Hence their demand for guidance by a scientific incentive mechanism. To this end, a mode is proposed for encouraging distribution side users interacting with the grid. According to the principle of incentive compatibility, a reasonable and effective price mechanism is suggested to clarify the contribution of flexible users to capacity saving. Relying on the transmission day-ahead market, the participation of users in distribution day-ahead interaction is designed including architecture, process and settlement. Based on the idea of decentralized decision-making, the interactive model of users' self-response and multi-round game of distribution network is simulated. The numerical example shows that, with the proposed mechanism, the costs and benefits arising from interaction can be fairly shared to deeply inspire user interaction with the distribution system, promote effective assets utilization of the grid, and achieve cooperation and mutual benefit as a win-win situation between distribution network and microgrids.

      • DONG Zhaoyang, ZHAO Junhua, WEN Fushuan, XUE Yusheng

        2014,38(15):1-11, DOI: 10.7500/AEPS20140613007

        Abstract:The traditional way of economic and social development,characterized by centralized utilization of fossil fuel energy,is gradually changing.On the other hand,the third industrial revolution is now rising.As the core technology of the third industrial revolution,the Energy Internet aims at facilitating large-scale utilization and sharing of renewable energy by integrating renewable energy and internet technologies.It will enhance the merging of electricity,transportation and natural gas networks,change the way of energy utilization,and finally achieve the goal of promoting sustainable economic and social development.Given this background,an overview of the Energy Internet is first provided,and a basic research framework developed.A definition of the Energy Internet is then suggested,followed by its basic architecture and main components.Several main research challenges to the Energy Internet,such as the wide-area coordination and control of distributed devices,the integration of the power system with the transportation system and natural gas network,as well as the cyber physical modeling and security,are next discussed in more details.

      • LU Zhigang1 , XIE Xiaowei2 , LI Xueping1

        2012,36(7):86-91, DOI:

        Abstract:In order to determine the optimal break point sets(OBPSs) for protection coordination in multi-loop network, four indices are introduced as the judgment criterion of OBPSs, the math model looking for OBPSs is developed. Then, based on the principle of bacterial colony chemotaxis algorithm, a new method of determining OBPSs is presented. Comparing with the existing method, the proposed method can find the optimal minimum break point set. An example analysis proves that this method is valid and applicable.

      • WANG Yelei, ZHAO Junhua, WEN Fushuan, XUE Yusheng

        2015,39(21):1-10, DOI: 10.7500/AEPS20150623001

        Abstract:The emergence and development of the power-to-gas (P2G) technique have made the bidirectional energy flow between power and natural gas systems possible. P2G represents a key technique in the emerging energy internet, and promotes the integration of multi-energy systems. By transforming electricity to gas, existing gas storage facilities can be used to mitigate the volatility of renewable energy generation. The modeling of future complex multi-energy systems with P2G functions is presented based on the “energy hub” framework, and a coordinated optimization model presented. A game-theory-based method is next proposed to attain market equilibrium in a multi-energy system. A 4-bus sample multi-energy system and a simplified Victoria gas-electricity combined network system in Australia are adopted for demonstrating the effectiveness of the presented optimization model and solving algorithm. This work is supported by National Basic Research Program of China (973 Program) (No. 2013CB228202) and National Natural Science Foundation of China (No. 51361130153, No. 51361130152).

      • GAO Hui,LI Huailiang,ZHAI Changguo,CHEN Liangliang

        2013,37(1):186-190, DOI: 10.7500/AEPS201207057

        Abstract:In order to improve the energy efficiency of electric vehicle(EV)power battery and increase the start-up power of EV,a maglev flywheel battery energy storage system with the active suspension controlled at five degrees of freedom is designed for EV.The system suspension control principle is expounded,and the radial single freedom transfer function of the maglev flywheel is established by referring to a digital proportion-integral-differential(PID)control algorithm.The frequency spectrum characteristic of the transfer function and the flywheel rotor trajectory curve are simulated,and the30000r/min rotation experiment on the maglev flywheel battery prototype is realized.The experiment results show that the maglev flywheel rotor is capable of high speed steady spin,and with good energy storing ability.The maglev flywheel battery energy storage system will assist the EV power battery work,improve the battery charge and discharge properties and prolong the service life of the motive power battery.

      • LI Peng, HUANG He, WU Xiaochen, HUANG Mei, YANG Yinguo, LI Ling

        2014,38(1):127-133, DOI: 10.7500/AEPS20130712005

        Abstract:Security and stability standards of power grids are the basic norm of power system planning and operation."Security and stability guide of power systems" is China's reliability standard which has been in use since 1980s.The guide defines several levels of contingency according to the severity,and requires different defense plans.It has played an important role in security and stability during the period of rapid development of power grids.In 2011,the Central Government of China promulgated"Regulations on accident investigation and handling of electricity safety emergency",which makes new requirements on grids and power companies from the perspective of load loss.Electricity utilities in China should review their security and reliability standards at present.The paper describes the security and stability standards carried out by the major Western developed countries,compares them with Chinese standards,and makes some useful suggestions for the next version of China's reliability standards.

      • XU Hongqiang, YAO Jianguo, NAN Guilin, YU Yijun, YANG Shengchun, ZHAI Mingyu

        2018,42(1):1-7, DOI: 10.7500/AEPS20170518001

        Abstract:With the construction of ultra-high voltage(UHV)AC/DC interconnected power grid, the advancement of new energy and the deepening of electricity market reform, significant changes have taken place in the operation of power grid in China, which makes higher requirements on the dispatching and control functions. Based on the integrated distribution and concentration deployment scheme of application functions, this paper gives an overview of the new features of the application function, i. e. , global, rapid and accurate, analyzes the technological support to realize such application functions, and points out the urgency of promotion basic work such as power grid model, operation data and management rules.

      • YANG Ting, ZHAO Liyuan, WANG Chengshan

        2019,43(1):2-14, DOI: 10.7500/AEPS20180706005

        Abstract:In order to promote the energy production and consumption revolution and build a clean, low-carbon, secure and efficient energy system, it is necessary to develop a new generation of power system and integrated energy system which are more intelligent. Artificial intelligence is one of the most disruptive technologies in the world, which has strong processing ability in computational intelligence, perceptual intelligence and cognitive intelligence. The application of artificial intelligence in power system and integrated energy system will change the traditional utilization mode of energy and promote the further intellectualization of the system. The contents of this review are as follows: the summary of artificial intelligence, the demand for artificial intelligence in power system and integrated energy system, and the various applications of artificial intelligence in the energy field. Finally, the paper presents the future challenges and opportunities faced by the energy field in the era of artificial intelligence.


    Editor in chief: Xue YuSheng
    Associate editor:Zhang BoMing
    Luo An, Wen FuShuan, Wang Qing
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