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      • XU Xinzhi, DU Ershun, GAO Yi, ZHANG Ning, LI Jun

        Available online:May 13, 2021  DOI: 10.7500/AEPS20201104004

        Abstract:Operation simulation and capacity planning tools in power systems play an important role in power system planning, operation and evaluation. In recent years, with the large-scale integration of renewable energy, the research results of models and methods for operation simulation and capacity planning are emerging one after another, and the corresponding software tools have also ushered in significant progress and updates. This paper summarizes a variety of mainstream software tools for operation simulation and capacity planning at home and abroad, and focuses on analyzing the characteristics of various software tools including general structure, temporal resolution, power flow models, unit commitment constraints, solving algorithms, etc. In addition, combined with the current research status and the development trend of the power system, related thinkings of the future operation simulation and capacity planning tools in the power system are proposed.

      • ZHANG Xihong, ZHAO Qi, CHEN Zhong, TIAN Jiang, DU Puliang, XING Qiang

        Available online:May 13, 2021  DOI: 10.7500/AEPS20201028004

        Abstract:Delay, packet loss and error codes of data transmission in information systems will cause the information collected by the distribution network control center to deviate from the true value. For this reason, a multi-scenario two-stage stochastic control method is proposed, which considers the information failure of the distribution network in the cyber-physical system. Firstly, the data and predicted values of each sampling point in the trend optimization cycle are discretized into different scenario sets based on the information failure conditions that may occur. With the goal of minimizing the total cost, the stochastic model predictive control is used to perform real-time rolling optimization of each scenario in the cycle and coordinate the output of various distributed energy sources. Secondly, in a shorter real-time correction cycle, according to the fine coordination of dispatchable abilities, the impact of information failure on the distribution network can be further reduced. Finally, in the improved IEEE 33-node distribution network, it is verified that the proposed method can effectively improve the safety and economy of the coordination and optimization of the distribution network when information failure is considered, and the difference and sensitivity of different information failure situations are also analyzed.

      • JIA Ke, HOU Laiyun, ZHENG Liming, BI Tianshu, LI Yinhong

        Available online:May 13, 2021  DOI: 10.7500/AEPS20201114003

        Abstract:With the rapid development of renewable energy, the proportion of renewable energy generation in some areas is more than 50%, which is in the transition from auxiliary power supply to main power supply. There are two problems in the calculation of short-circuit current of existing renewable projects. Firstly, the fault characteristics of renewable energy are characterized by 1.2 to 2 times of rated current, which leads to poor calculation accuracy and is difficult to meet the protection requirements. Second, the existing short-circuit current setting calculation software does not support iteration, so it is unable to update the fault current of renewable energy according to the change of node voltage, reflecting the characteristics of voltage controlled current source. To solve this problem, firstly, based on the refined analytical model of fault characteristics of renewable energy, combined with the field fault recording data, the voltage-current mapping relationship is constructed to meet the requirements of practical engineering calculation. Then, the fault area is divided according to the degree of node voltage drop and the connection relationship between nodes after power grid fault, and the local iteration calculation is carried out according to the practical calculation formula of renewable energy in the fault area to solve the node voltage and short-circuit current of the network, so as to avoid the convergence problem caused by the global iteration and shorten the calculation time. Finally, the calculation effect of the proposed method is verified by engineering calculation software.

      • ZHANG Jianxin, XIE Lirong, DU Liwei, ZHA Yuxin

        Available online:May 13, 2021  DOI: 10.7500/AEPS20200925009

        Abstract:The existence of interference signals, such as decaying direct current (DDC) components and high-order harmonics, makes certain errors in detecting the amplitudes and phases of fundamental frequency signals in the distortion signals of the power grid. The time constant of the DDC component usually exceeds 45 ms, and the duration is longer. To solve this problem, this paper proposes a half-cycle four-point sampling detection algorithm for DDC components in the distorted signal. The proposed algorithm can greatly shorten the detection response time of the DDC component. For the distorted signals that contain both DDC components and high-order harmonics, the above DDC component detection algorithm is combined with the high-order harmonic detection algorithm in the dq coordinate system after the half-cycle integration of the distorted signals. Then, the influence of interference signal can be filtered out at the same time in a unit half-cycle of the power frequency, and the fundamental-frequency component in the distorted signal can be detected accurately. Finally, a semi-physical real-time simulation model in MATLAB/Simulink is built to verify the effectiveness of the proposed algorithm in terms of detection accuracy and response time.

      • YUN Qiuchen, TIAN Liting, QI Ning, ZHANG Fang, CHENG Lin

        Available online:May 13, 2021  DOI: 10.7500/AEPS20200828001

        Abstract:For the optimal combination of heterogeneous resources of virtual power plant, a response characteristic model including demand response, flexible controllable load, and distributed power generation is proposed. Based on the control authority of the virtual power plant over interactive resources, the interactive resource response power is divided into risk-free and risk assets. Then the resource response allocation problem is mapped to the asset weight allocation problem in the modern portfolio theory. The portfolio risk is used to measure the uncertainty of the user’s response to electricity, and the optimal combination model is established with the goal of maximizing the expected return. Based on the decentralization of interactive resources, the virtual power plant is involved in congestion management, and the proposed method is verified on the CIGRE 20 kV medium-voltage distribution network system. Simulation results verify the practicability of the proposed model.

      • LIU Lu, CHENG Haozhong, WU Yaowu, CHEN Haoyong, ZHANG Ning, WANG Zhidong

        Available online:May 13, 2021  DOI: 10.7500/AEPS20201114002

        Abstract:In order to deal with the consumption problem caused by the connection of high proportion of renewable energy, the transmission network planning theory based on multi-scenario technology, robust optimization technology and coordinated planning technology is proposed, which is composed of four different planning methods in different applicable conditions or demand scenarios, i.e., multi-scenario based random planning method of transmission network, probability-driven based robust planning method of transmission network, coordinated planning method of network-source considering multi-source complementarity and transmission network planning method coordinated with distribution network. It can improve renewable energy consumption from the perspective of transmission network planning under the premise of security and stability. On this basis, the future transmission network planning methods are prospected, and the possible research directions are proposed, including satisfying higher security and stability requirements, coordinating more extensive source-network-load-energy storage flexible interaction, promoting the application of big data and exploring the incentive space of power market mechanism. The corresponding research difficulties and feasible solutions are discussed.

      • WANG Qianggang, TIAN Yuhe, WANG Jian, HU Fangxia, ZHOU Niancheng

        Available online:May 12, 2021  DOI: 10.7500/AEPS20201203003

        Abstract:The electric vehicle is connected to the distribution network through the converter interface of the charging pile. The reactive power regulation capability of converters can improve the voltage profile and operation efficiency of the distribution network. This paper proposes a coordinated day-ahead and real-time optimization model for the distribution network considering reactive power compensation of charging stations. Firstly, a day-ahead optimization model with the optimization objective of minimizing the operation cost of the distribution network is established. The day-ahead active power of the charging station, the switching of capacitor bank and on-load tap changer are determined. According to the results of day-ahead optimization and real-time parameters of electric vehicles, the real-time optimization model of active and reactive power of electric vehicles with hierarchical coordination between the distribution network and the electric vehicle charging station is established. In order to ensure that each electric vehicle can reach the target state of charge when it leaves, the impact of the state of charge of the electric vehicle at the previous moment is considered to adjust the boundary of its current state of charge. Finally, the effectiveness of the proposed model is verified by the test of IEEE 33-bus system.

      • MO Jingshan, YAN Wei, WEN Xu, ZHANG Ziwei

        Available online:May 12, 2021  DOI: 10.7500/AEPS20210107003

        Abstract:The results of tertiary voltage control for AC/DC interconnected system should satisfy the independent control mode of converter station. Therefore, an optimization method for static reactive power of AC/DC system considering independent control constraints of converter station is proposed. The basic assumption of the new model is that the initial operation state of DC power and discrete voltage regulation devices remain unchanged during the period of tertiary voltage control. Based on the conventional static reactive power optimization model of AC/DC system, the dead zone control constraints of local reactive power balancing of DC system and the adjustable range constraints with non-fixed boundary of auxiliary power supply for DC system are further considered. The problem is solved by the interior point method. A UHVDC converter station with its nearby AC power grid in Northeast China is simulated to verify the effectiveness of the proposed method. The simulation results show that the proposed method can reduce the risk of frequent operation of discrete voltage regulation devices and realize the coordinated control of the transient and steady-state reactive power of converter station.

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      Volume 45,2021 Issue 10

      • LI Kexin, GUO Hongye, CHEN Qixin

        2021,45(10):1-8, DOI: 10.7500/AEPS20201104002

        Abstract:On August 14th and 15th, 2020, the power system experienced two consecutive days’ load shedding in the accident of electricity restriction in California, USA. Based on the comprehensive consideration of the high-penetration renewable energy and the unique market mechanism design of the California Electric Power System, this paper analyzes two topics which are the causes of the process of electricity restriction in California and the role of the regional market mechanism in the electricity restriction. To this end, firstly, combined with the actual market operation data, this paper focuses on the quantitative analysis of the influence of two aspects: renewable energy with net load and imported electricity in the accident of electricity restriction in California, USA. Secondly, focusing on the regional power trading mechanism that is being promoted in California and its surrounding areas, an in-depth analysis of the operation mode and implementation logic of the mechanism of the western energy imbalanced market (WEIM) is carried out. The impact of the mechanism of WEIM on the accident of electricity restriction is analyzed and evaluated. Finally, after summarizing and discussing the experience and lessons of the accident of electricity restriction, combining with the conditions and progress of Chinese electricity market construction, relevant suggestions are made for the future regional collaboration, mechanism coordination and construction path of Chinese electricity market.

      • >Special Topics
      • ZHANG Yuanyuan, HE Jian, TU Jingzhe, AN Xuemin, LI Lin, ZHOU Qinyong, GUO Yiwei

        2021,45(10):9-16, DOI: 10.7500/AEPS20201117004

        Abstract:In view of the disaster situation of city power grid interruption caused by emergencies, IEC 63152 standard puts forward the disaster prevention concept of ensuring the reliable electric power supply to maintain basic city service uninterrupted, which involves four elements, i. e., city service continuity, business continuity plan, electricity continuity plan, and electricity continuity system. Through the in-depth interpretation of the relevant requirements and guidelines, basic concepts and methods, and means of establishment, it is clarified how to build a complete disaster prevention system of city electricity continuous supply among the four elements, which should focus on issues such as configuration of standby electricity supply, evaluation of necessary electricity capacity required by city services, inter-regional cooperation relationship, establishment of management timetable. Finally, some considerations and suggestions on the follow-up work of the standard and the construction of the power grid in China are given.

      • >Basic Research
      • ZHANG Xiaohua, XU Wei, WU Feng, REN Xiancheng, FENG Changyou

        2021,45(10):17-24, DOI: 10.7500/AEPS20200310001

        Abstract:Cross-region cascading failures seriously threaten safe operation of AC/DC hybrid power systems, and dispatching operation is facing tremendous pressure and accident risk. An intelligent tracing and prediction method for characteristic events is proposed, which integrates the knowledge graph and machine learning algorithm, so as to realize online tracing and prediction of cascading failure chains. The operation state and fault information of power grids are taken as input characteristic variables. Based on the physical mechanism analysis and Pearson coefficient, the key characteristic variables are extracted, and the relationship between characteristic events is judged by a support vector machine. A bi-level structure of the knowledge graph is established to match the association relationship between the upper and the lower level events based on the types of detected characteristic events. According to the judgment result of the association relationship of characteristic events and the time sequence characteristic, the evolution path of cascading failures is identified based on the depth-first searching strategy. The effectiveness of the proposed method is verified by a case study of online data from an actual power grid.

      • LIU Lu, LI Linzhi, LU Tianqi, WU Hao

        2021,45(10):25-33, DOI: 10.7500/AEPS20200611004

        Abstract:In the power system, the identification of critical links is of great significance for the propagation mechanism analysis of cascading failures, the formulation of preventive measures and the improvement of system reliability. In this paper, the stochastic approach for link-structure analysis (SALSA) used in the web link analysis is introduced into critical link analysis for cascading failures in the power system, and the concepts of “propagative branch” and “vulnerable branch” are proposed. Based on massive cascading failure simulation data, the roles of branches in the failure propagation are identified, as well as the high-risk failure propagation relationships which will cause serious blackout consequences. The verification on the IEEE 39-bus system and an actual provincial power grid in China shows that the proposed method can effectively identify the critical links of the system, and the mitigation measures aiming at critical links can effectively reduce the risk of cascading failure blackouts.

      • LI Jiamin, YANG Hongying, YAN Liping, LIU Daowei, LI Zonghan, XIA Yuanqing, ZHAO Yan

        2021,45(10):34-41, DOI: 10.7500/AEPS20200309001

        Abstract:In order to quickly and accurately evaluate the stability of the power system after a transient fault occurs in the power system, and to solve the bias problem of the model caused by sample imbalance, an integrated transient stability assessment method for power systems based on the improved loss function is proposed. Firstly, based on the short-term measurement data after the fault clearing, a new integrated model that combines one-dimensional, two-dimensional single-channel and two-dimensional multi-channel convolutional neural networks is designed to realize the end-to-end abstract feature extraction and transient stability classification. Secondly, the loss function in the model training process is improved to enhance the fitting degree of unstable samples for increasing the weights of the misclassification samples. Thus, the global accuracy is improved, and the missing alarm rate of unstable samples is reduced. Moreover, the influence of the output threshold of the integrated model on the recall rate of instable samples is analyzed in this paper. Finally, the simulation results of IEEE 39-bus system and IEEE 145-bus system verify the effectiveness of the proposed algorithm.

      • LIU Junlei, CAO Na, QIAN Feng, ZHAO Xu, ZHANG Zijie, YU Qun

        2021,45(10):42-49, DOI: 10.7500/AEPS20200623006

        Abstract:In the wind farm, improper setting of control parameters of the converter for the wind turbine may cause the power oscillation of the unit and other units, which threatens the normal operation of the power system. In order to study the influence of control parameters of converters on the unit oscillation in the wind farm, taking the doubly-fed induction generator (DFIG) based wind turbine as an example, first, the converter control parameters are considered, and the energy function of the DFIG-based wind turbine is derived. Then, the influence of control parameters of converters on the energy flow power and energy consumption of the DFIG-based wind turbine is analyzed. Next, in view of the different control parameters of the unit converter in the wind farm, whether the units in the wind farm will oscillate and the influence of the unit on other units are studied. Finally, the model is built on PSCAD/EMTDC platform, and the influence of control parameters of the converter on the energy flow power and energy consumption of the wind farm is analyzed. The results show that the improper setting of control parameters of the unit converter not only causes free oscillation of the unit, but also causes oscillation of other units in the wind farm.

      • WANG Zhenhao, LI Bowen, CHENG Long, LI Guoqing, LI Dexin

        2021,45(10):50-58, DOI: 10.7500/AEPS20200729004

        Abstract:For the purpose of accurately realizing the stability evaluation and time domain simulation of multi-voltage-level DC distribution networks and improving the efficiency of system analysis, an average dynamic phasor modeling method of the multi-voltage-level DC distribution system based on current reconstruction of the dual-active-bridge (DAB) DC transformer is proposed. The dynamic phasor of each variable in the system is taken as state or input variables, and the complexity of the model is reduced by neglecting its high-order component. The equivalent phase shift duty cycle is regarded as the modified algebraic variable by introducing the error correction, and the deviation caused by neglecting the high-order dynamic phasors is reduced, so that the accurate characterization of the DC component in the average dynamic phasor model is realized. Fourier series (FS) is used to reconstruct the transformer current which cannot be precisely described. Thus, the AC variables in the average dynamic phasor model are accurately characterized. Based on the average phasor model of a single DAB transformer, the DC line equation is introduced to form an extensible global model of the system. By analyzing and comparing the average dynamic phasor model and the electromagnetic transient model of a multi-voltage-level DC distribution network based on MATLAB/Simulink, the correctness and accuracy of the proposed average dynamic phasor model and current reconstruction method are proven in the two scenarios of sudden load increase and line breakdown. Also, the stability of the system global model with changing the transformer frequency and leakage inductance is verified.

      • LYU Yongqing, DOU Xiaobo, YANG Dongmei, HE Guoxin

        2021,45(10):59-67, DOI: 10.7500/AEPS20200811007

        Abstract:To solve the coordination problems between energy storage power stations when participating in frequency regulation and traditional units and the influence of communication delay, this paper designs a load frequency robust control method for energy storage power station considering the correction of state of charge and communication delay. Firstly, the regression and amendment link of state of charge (SOC) is designed to coordinate with traditional units when the energy storage power station participates in the frequency control to realize the SOC margin adjustment. Then, considering the effect of communication delay, this paper designs a delay system model of regional power grids with regression and correction of SOC in energy storage power stations. Secondly, considering the impact of communication delay on design performance of system control, the system robust controller is designed for load frequency control of energy storage power stations based on the delayed marginal calculation of the load frequency control system to restrain power disturbance of renewable energy sources and realize the quick recovery of system frequency. Finally, the simulation of the load frequency control system is implemented in the MATLAB/Simulink platform, and the validity of the proposed strategy is verified.

      • CHENG Haozhong, ZHANG Chengming, LIU Lu, ZHANG Xiaohu, LI Gang, WANG Zheng

        2021,45(10):68-76, DOI: 10.7500/AEPS20200825012

        Abstract:With the increase of power load density and network structure tightness and the uncertainty caused by renewable energy integration, the problem of excessive short-circuit current becomes prominent. This paper proposes a robust planning method for power generation and transmission system that can satisfy the short-circuit current limit with renewable energy integration. Firstly, the calculation method of short-circuit current considering network topology and power supply integration is improved, where network topology optimization and unit startup/shutdown are employed to optimize the short-circuit current level. Secondly, a three-level robust planning model of the generation and transmission system is built by the adaptive polyhedral uncertainty set considering the uncertainty of renewable energy output and N-1 random failure. The top level is the planning decision problem with short-circuit constraints, whose goal is to minimize the sum of the annual investment cost of transmission network expansion and power construction as well as the annual operation cost in the worst scenario. At the middle level, the worst-case scenario including the combination of renewable energy output and N-1 random failure is found. The lower level is the optimal power flow problem satisfying the operation constraints in uncertain scenarios. Then, the three-level problem is transformed into a bi-level problem by dual transformation and solved by the column-and-constraint algorithm. Finally, the results of IEEE 24-bus system show that the planning scheme can meet the short-circuit current requirements under the uncertainty of renewable energy output.

      • NI Shuang, CUI Chenggang, YANG Ning, CHEN Hui, XI Peifeng, LI Zhenkun

        2021,45(10):77-85, DOI: 10.7500/AEPS20200830003

        Abstract:The distribution network with distributed generators has problems such as inaccurate power flow modeling, power communication conditions, and difficulty in coordination of various reactive power compensation equipment. The problems bring challenges to the online optimization for reactive power of the distribution network. This paper proposes a multi-time-scale online optimal operation scheme for reactive power of the distribution network based on the method of deep reinforcement learning (DRL). The scheme converts the problem of the online optimization for reactive power of the distribution network into a Markov decision process (MDP). In view of the different adjustment speeds of different reactive power compensation equipment, two time scales are designed to optimize the configuration of the discrete adjustment equipment and the continuous adjustment equipment. This scheme can track the status of the distribution network in real time, make online decisions about the optimization for reactive power regulation equipment, and does not rely on accurate power flow models. It is suitable for partial observable distribution networks that are complex and changeable and have poor communication conditions. Finally, a numerical example verifies the effectiveness and robustness of the proposed method.

      • ZHAN Xiangpeng, YANG Jun, HAN Sining, ZHOU Ting, WU Fuzhang, LIU Shouwen

        2021,45(10):86-96, DOI: 10.7500/AEPS20200414006

        Abstract:In the electricity market environment, charging stations (CSs) can reduce the cost of electricity by optimizing the bidding strategy, even gain profits by selling electricity. In this paper, the potential of electric vehicles (EVs) to become flexible storage and load resources is considered, and the bidding strategy of CSs in the day-ahead market and real-time market is proposed. First, the compression method of the EV clustering model in CSs is proposed based on Minkowski method. The prediction model of day-ahead schedulable potential capacity and the evaluation model of real-time schedulable potential capacity are established. Meanwhile, the strategic bidding model of CS in the electricity retail market is established considering the non-cooperative game among CSs. The model is transformed into a generalized Nash equilibrium problem based on the stationary point method. Then, the two-stage market trading mode is proposed based on day-ahead quotation and real-time declared quantity, which is compared with the cooperative bidding mode, the exogenous price mode and the centralized scheduling mode. Finally, the simulation on a 38-bus distribution system shows that the proposed calculation method of schedulable potential capacity can encapsulate the EV cluster as a generalized energy storage device, which can reduce the dimensions of the model. The strategic bidding model based on the schedulable potential can tap the storage and load potential of EVs and realize the orderly interaction between EVs and power grids.

      • ZHAO Tianhui, ZHANG Yao, WANG Jianxue

        2021,45(10):97-105, DOI: 10.7500/AEPS20200622003

        Abstract:For mass power load data, a method based on density-based spatial clustering and outlier boundaries is proposed to identify the load outlier. Firstly, the density-based spatial clustering method is used to classify load curves into normal and abnormal power consumption patterns. Also, the load curves with normal power consumption pattern are classified into different load levels. Then, the outlier boundaries are built using the confidence interval of load expected value and the inter-quartile range of the deviation between load sample and sample average at different load levels. Considering the contingencies of atypical power consumption behavior, the obtained outlier boundaries are corrected by time offset of power consumption, and outlier boundaries for abnormal power consumption patterns are built. Finally, the proposed method is tested in the example with the load data sets of residential and industrial users. Compared with the traditional method, the precision of the proposed method is improved over 10% on average, and the comprehensive evaluation index is improved over 4% on average.

      • WU Yuqi, YE Yuqing, MA Xiao, LI Zhengtian, LIN Xiangning, XU Haibo

        2021,45(10):106-114, DOI: 10.7500/AEPS20201103008

        Abstract:The problems in existing islanding detection research is that the analysis of the non-detection zone of the over/under voltage detection method and the over/under frequency detection method in the droop control strategy are not complete, the influence of related parameters on the non-detection zone is not clear and the analysis method is difficult to be applied to the complicated actual microgrid. Firstly, four general equations of the droop control equation, the load equivalent equation, the line power equation and the steady-state power balance equation are obtained based on the analysis of actual microgrid operation conditions equipped with distributed resources in the droop control strategy, and solved iteratively by Newton-Raphson method. Then the influence of the load equivalent model, line impedance parameter and droop control performance on the non-detection zone distribution is explored in a visual way, and the characteristics of the non-detection zone are revealed. Finally, using the simulation software, the correctness and accuracy of the analysis of the non-detection zone are verified, and the excellent performance of solving algorithm for the non-detection zone is proven to be suitable for different operation conditions.

      • >Application Research
      • SHEN Chao, SHUAI Zhikang, CHENG Huijie

        2021,45(10):115-123, DOI: 10.7500/AEPS20201002001

        Abstract:The injected current of current-controlled converters has unnegligible effect on the transient synchronization stability of virtual synchronous generators (VSGs) in the grid-connected paralleled power supply system, which may result in irreversible instability problem of the system. Studying the interaction mechanism among different converters in the paralleled power supply system is an important prerequisite for ensuring stable operation of the system during the transient period. This paper builds the transient interaction model of VSGs and current-controlled converters. It is found that the effect of injected current on the transient stability of VSG is determined by the power coupling terms. On this basis, the effect of phase angle of injected current on the transient stability of VSG is studied by using equal area criterion (EAC) in both purely inductive and resistive-inductive networks. The research result shows that, when the sum of the phase angle of injected current and the admittance angle of paralleled line is close to -90°, the system stability will be enhanced. The simulation results based on PSCAD/EMTDC and the experimental results based on RT-LAB verify the correctness of the theoretical analysis.

      • WEI Zheng, JI Qiuhua, WANG Wei, WANG Tong, WANG Junhui, WANG Tengfei

        2021,45(10):124-131, DOI: 10.7500/AEPS20200805003

        Abstract:It is one of the challenges faced in practical engineering applications of the self-synchronous voltage source inverter (SVI) to realize balance control of the three-phase current under asymmetric grid voltage conditions when connected to the grid, and take into account the stability of the terminal voltage control when it runs independently off the grid. First, under the asymmetric condition of the power grid, on the basis of a brief description of the working principle of the SVI, this paper analyzes in detail the limitations of applying in conventional positive and negative sequence separation control to SVI, and the instability mechanism when the system operates independently from the grid. Then, based on the single-mode control idea of the SVI, a suppression strategy of SVI negative sequence current based on a quasi-resonant controller is proposed, which achieves the balance of current output to the grid under the asymmetric grid condition. At the same time, the system stability of the SVI is guaranteed when it switches between on-grid and off-grid modes and operates off-grid (including multi-machine parallel) independently. Finally, simulation and experimental results verify the correctness and effectiveness of the proposed system control strategy.

      • LIU Jian, LIU Lei, LIN Sheng

        2021,45(10):132-139, DOI: 10.7500/AEPS20200410009

        Abstract:Commutation failure is one of the most common faults in high voltage direct current (HVDC) transmission systems. In order to mitigate the inverter commutation failure in DC transmission systems, the link of commutation failure prediction control (CFPREV) is widely used in practical projects at present. However, this link is susceptible to the influence of the initial fault angle. At some initial fault angles, the variation trend of zero-sequence voltage index is contrary to the variation trend of fault severity, which will seriously restrict the starting speed of CFPREV and hinder the suppression of commutation failure. Based on CFPREV, an improved CFPREV method based on waveform similarity detection is proposed in this paper. Pearson correlation coefficient is used to represent the changes of zero-sequence voltage waveform in real time, so as to quickly detect faults and avoid the shortcomings of the original CFPREV which starts slowly at some initial fault angles. The simulation results based on the CIGRE standard test model show that the proposed control strategy can eliminate the influence of the initial fault angle on the original CFPREV, improve the operation sensitivity of CFPREV link, and inhibit the initial commutation failure of HVDC transmission system to a certain extent.

      • LI Bin, MAO Qiyang, HE Jiawei, YU Yang, SHAO Qingzhu, LI Ye

        2021,45(10):140-148, DOI: 10.7500/AEPS20200804003

        Abstract:Accurate fault location is the key technology for ensuring fast fault checking and clearing in power systems. The fault location method based on traveling-wave natural frequency has significant technical advantages in the line commutated converter based high voltage direct current (LCC-HVDC) system. However, through the analysis, it is found that the natural primary frequency of the fault traveling wave in the voltage source converter based HVDC (VSC-HVDC) grid is very low and the available data window is very short, which results in a large error for the location method based on the main component of natural frequency. Aiming at the above issue, it is proposed to reclose the residual current breaker (RCB) during reclosing period to create a sufficient transient data window. In addition, the fault location method based on primary/secondary frequency iterative calculation and verification is proposed. Compared with the traditional fault location method using the natural frequency at the beginning of the fault, the proposed method can significantly improve the fault location accuracy in VSC-HVDC grids. Moreover, the location deviation problem caused by the false spectral peak phenomenon of the multiple signal classification (MUSIC) algorithm is also avoided. Finally, a large number of simulation cases are carried out to verify the feasibility and superiority of the proposed method.

      • JIANG Chunbing, ZHAO Chengyong

        2021,45(10):149-156, DOI: 10.7500/AEPS20200824005

        Abstract:The suppression of direct current (DC) fault current in the DC power grid is one of the key problems to be solved urgently. In order to suppress the rising rate and the peak value of fault current, this paper comprehensively considers the effect of inductors and capacitors on fault current suppression in the DC circuit breaker (DCCB) with the capacitive current limiter. And the fault current characteristics before and after the throw-in of capacitive current limiter are analyzed. Then this paper proposes the optimal configuration scheme of the DC reactor and the capacitor current limiter under the constraint conditions of the breaking capacity limit of DCCB and the current limit of power electronic devices on the arm of the converter. Finally, a six-terminal DC power grid model is built in the PSCAD/EMTDC, and the parameters of DC reactor and capacitive current limiter are optimized with the multi-objective function of the inductances of DC reactors, the voltage across capacitive current limiters and the breaking current of DCCB. The optimal configuration schemes of the DC reactor and the capacitive current limiter are provided for different electrical application scenarios.

      • LI Yanjun, PEI Wei, XIAO Hao, LIU Youbo

        2021,45(10):157-165, DOI: 10.7500/AEPS20201117002

        Abstract:As a new type of demand response resource, the grid connection scale of microgrids is increasing. However, due to the uncertainty of the internal resource combination and the random output fluctuation of the sources and loads in microgrid, the demand response characteristics of its participation in the operation of the power grid also show great uncertainties so that the operation risk of the distribution network is greatly increased. In this regard, this paper proposes a new mechanism for the demand response characteristic package of microgrids based on deep learning and optimal operation of the distribution network. It can package the demand response characteristics of microgrids by a data-driven approach to avoid the analysis of the internal model of microgrids. With fully use of the weather information and price data, a multi-dimensional sequential demand response package model of microgrids based on long short-term memory (LSTM) is established. On this basis, an optimization operation model of distribution network is constructed, and a model solution strategy based on the improved particle swarm optimization (IPSO) algorithm is proposed to minimize the risk of the voltage over-limit and network loss in distribution networks. Through the analysis of the 33-node distribution system with microgrid group, the results show the effectiveness of the proposed demand response package model of microgrids and the superiority of the IPSO algorithm.

      • ZHONG Jiayong, XIONG Xiaofu, HE Yingchun, SHAN Rongrong, JIANG Honglang, LI Shuangquan

        2021,45(10):166-173, DOI: 10.7500/AEPS20200629007

        Abstract:In the background of the Internet of Things for distribution network, the workload of manual access for intelligent terminals and end devices in massive distribution station areas is huge, and there are problems such as difficulty in maintenance of edge-end topology and information interaction. Therefore, this paper proposes a plug-play and topology identification method for intelligent terminals in the distribution station area. Firstly, according to the “cloud-tube-edge-end” hierarchical system of the Internet of Things for distribution network, the architecture scenario is constructed for terminal equipment such as intelligent terminals and smart meters in the distribution station area. On this basis, the corresponding plug-play mechanism is proposed. Secondly, an automatic topology identification method for intelligent terminals and end devices in the distribution station area is proposed. Finally, by building an experimental system, the proposed plug-play and topology identification method is verified and analyzed from three parts: terminal access verification, terminal software upgrade and failed terminal exit. The experiment results show that the proposed method has good scalability and fault tolerance ability, and can realize automatic operation and maintenance of plug-play and topology correlation between intelligent terminals and end devices in the distribution station area.

      • >Survey
      • CHEN Yiping, ZHUO Yingjun, LIU Yingshang, GUAN Lin, LU Cao, XIAO Liang

        2021,45(10):174-183, DOI: 10.7500/AEPS20200726004

        Abstract:With the increasing penetration of non-synchronized power supplies, the inertia of the power grid decreases gradually and the rate of change of frequency (RoCoF) becomes higher after the disturbance, which brings huge challenges to the frequency regulation. In recent years, the concept of fast frequency response (FFR) has been proposed, and it is applied prior to the primary frequency response (PFR) to make time for the PFR, so that the low inertia system will not reach the threshold of the system under frequency load shedding (UFLS) before the PFR response. This paper summarizes the progress of FFR market of other countries from several aspects, such as typical FFR resources, designs of auxiliary service products, market transactions, and application examples. Combining with the frequency regulation needs of the power grid of China to cope with the low-inertia system in the future, the research trend of FFR technology is explained, and suggestions and prospects are put forward for the construction of the FFR market in China.