Online: September 27,2021 DOI: 10.7500/AEPS20201231004
Abstract:Aiming at the problem that separate aggregation of wind power and photovoltaic (PV) time series data changes the correlation between wind power and PV series, the factor analysis-extreme learning machine (ELM) aggregation method is adopted. Firstly, the z-score standardized wind power-PV original daily scene set is decomposed into horizontal components and fluctuating components of daily scene sets. Secondly, affinity propagation (AP) clustering is carried out for the horizontal components of daily scene sets to obtain K type scene clusters. 2n days horizontal components of daily scene sets are obtained through stratified sampling. The corresponding 2n days original daily scene sets is selected from the standardized wind power-PV original daily scene sets, and n days training set and n days testing set are obtained respectively. Then, the mapping relationship between the horizontal components of daily scene sets and the original daily scene sets is obtained through the ELM, and the fitting power daily scene set is output. Finally, through the anti-standardization, the n days wind power and PV power aggregation series are obtained respectively. The accuracy and feasibility of the proposed method are verified by probability statistical indices, correlation coefficients and simulation results.
Online: September 27,2021 DOI: 10.7500/AEPS20210412002
Abstract:With the large-scale development of offshore wind power, the harmonic problem caused by the integration of offshore wind power has become more and more prominent, thus the modeling and analysis are urgently needed. The modeling of submarine cable in the harmonic frequency range is one of the important work to tackle this problem. The calculation method for electrical parameters of submarine cable in the harmonic frequency range is studied, which provides a basis for the modeling of the submarine cable. First, the definition of cable electrical parameters is given, and then the calculation process and formulae for the electrical parameters of submarine cable are summarized. The applicability of the calculation formulae is also demonstrated. Finally, the electrical parameters of three typical submarine cables are calculated. Results show that both the positive sequence parameters and the zero sequence parameters of the cable will change greatly with the frequency, and the characteristics of cable electrical parameters changing with frequency must be considered when performing harmonic analysis.
Online: September 27,2021 DOI: 10.7500/AEPS20210413004
Abstract:In order to reduce the ride-through cost of the flexible high voltage direct current (HVDC) system with wind farm integration when a low-voltage fault occurs in the AC main grid, this paper proposes a grid fault ride-through strategy in which the DC energy dissipation equipment and the DC choppers in wind turbines work together. The wind farm will reduce its DC power output with the coordination of the sending-end converter in the grid fault. The DC energy dissipation equipment is only required to limit the DC voltage increase in the early stage of the grid fault before the output power of the wind farm have been reduced. Therefore, this strategy could greatly reduce the volume of the DC energy dissipation equipment. On this basis, the proposed strategy integrates the energy dissipation resistor of the DC energy dissipation equipment into the receiving-end modular multilevel converter (MMC), to further reduce the unloading cost. Finally, a simulation example of the flexible HVDC system with wind farm integration is constructed in the PSCAD/EMTDC simulation software, which verifies the correctness and effectiveness of the proposed fault ride-through method.
Online: September 27,2021 DOI: 10.7500/AEPS20210221003
Abstract:A reasonable system capacity configuration scheme is an important basis for the development and utilization of renewable energy. An optimal configuration method of capacity for the grid-connected wind-photovoltaic(PV)-pumped-storage joint operation system is proposed. The method establishes a system model with the optimization objectives of the minimum cost, the maximum economic benefit and the minimum carbon emission. Based on the real data of a coastal island in southeast China, the model is solved by fast and elitist non-dominated sorting genetic algorithm-Ⅱ(NSGA-Ⅱ). Then, gray relation analysis (GRA) is introduced to achieve an unbiased trade-off strategy to obtain the optimal capacity configuration scheme. The results show that the joint operation system can achieve continuous and stable operation on the basis of maximum utilization of wind and solar energy. It is feasible to introduce GRA to determine the optimal capacity configuration scheme, and the carbon emission of the joint operation system in the whole project cycle decreases with the increase of the grey correlation degree. Increasing the access rate of wind and PV power appropriately can reduce the system cost, improve economic benefits and reduce carbon emissions.
Online: September 27,2021 DOI: 10.7500/AEPS20210401005
Abstract:In order to improve the ability of line commutated converter based high voltage direct current(LCC-HVDC) system to resist commutation failures and improve the dynamic characteristics of the LCC-HVDC system during the fault period, this paper proposes a compound line commutation converter (LCC) topology based on thyristor-type full bridge sub-modules (T-FBSMs). The compensation of commutation voltage and the suppression of DC current rise can be realized by switching the control modes of T-FBSM during the fault, which improves the commutation failure immunity. Then, the coordinated control strategy of the T-FBSM and the converter valve are studied, and the electrical parameters of T-FBSM is designed. Finally, different simulation cases are set in the PSCAD simulation environment to verify the voltage and current stress and the commutation failure suppression effection of the proposed topology. The results show that the proposed coordinated control strategy of the compound LCC topology and the designed electrical parameters of T-FBSM are rational and effective, and the compound LCC topology can effectively reduce the commutation failure probability and improve the recovery characteristics of the system.
Online: September 26,2021 DOI: 10.7500/AEPS20210603005
Abstract:After a large-scale and long-term blackout accident in the distribution network under extreme disaster events, the active distribution network with distributed energy and emergency power supply vehicles (EPS) can form an island to supply power for the power loss load. Before the completion of fault repair, aiming at the problem that the unfairness of the sustainable restoration time of each key load with the same weight leads to the decline of customer satisfaction. This paper establishes a two-layer model of dynamic islanding equilibrium recovery, which considering the scheduling of EPS. It sets the optimal balance of critical load restoration and the maximum economic benefit of distribution network as the upper and lower objective functions, and realizes the fair and balanced restoration of loads with the same weight in the outage period. At the same time, in order to reduce the cost of EPS scheduling and load outage loss, based on the two-layer model above and Dijkstra algorithm, an optimal scheduling method of EPS supported by traffic network model is established, and the best candidate access node and optimal scheduling path are obtained. Then, the original mathematical model is transformed into a mixed integer linear programming problem by using big-M and other linearization methods. Finally, a modified PG&E 69-bus and traffic network are used to verify the effectiveness of the proposed method in improving the reliability, equilibrium and economy of power supply in the fault stage.
Online: September 26,2021 DOI: 10.7500/AEPS20210428008
Abstract:Typhoon and torrential rain disasters occur frequently in coastal areas, which is very easy to cause accidents such as tower falling and line disconnection of transmission lines. Therefore, an evaluation method of tower falling and line disconnection accidents considering typhoon and torrential rain disasters is proposed for 110 kV transmission line. Firstly, typhoon and torrential rain load models are established respectively to describe the wind and rain load at any position in the typhoon wind field. The finite element models of different transmission tower types of 110 kV line are established respectively. Considering the correlation of wind and rain loads, the dynamic response of line and tower under wind and rain loads is analyzed. Based on the structural reliability theory, the probability expressions of tower falling and line disconnection are derived, the mechanism effects of different tower types, uses and wind angles on tower falling are studied, the weak links of power grid are analyzed, and the tower falling and line disconnection accidents of 110 kV line under typhoon and torrential rain disasters are evaluated. Finally, the simulation uses the actual power system and real typhoon data in a region of China to verify the applicability of the proposed assessment method.
Online: September 26,2021 DOI: 10.7500/AEPS20210423011
Abstract:A regional short-term load forecasting method based on virtual similar days and dual-stage attention-based long and short time pattern network (DA-LSTPNet) is proposed for the demand of the refinement of short-term load forecasting. To obtain the fine-grained real-time meteorological data matching the load, a meteorological virtual similar day containing fine-grained meteorological data is firstly obtained using gray correlation and correlation weighting method based on the coarse-grained meteorological data. Then, the maximum information coefficient (MIC) is used to analyze the nonlinear correlation between meteorological feature information and load. And the MIC-weighted selection algorithm for load virtual similar day is constructed to solve the problem of excessive local similarity or even non-similarity caused by selecting historical days as traditional load similar days. Finally, in order to address the problem that the relationship between characteristic factors and local load fine-grained variation, the DA-LSTPNet is constructed to effectively explore the characteristics of long-term macroscopic and short-term local variation of load feature data for the day-ahead short-term load forecasting. The experimental simulation is based on the actual load data of the power grid in a certain area of southern China. The various forms of simulation are used to demonstrate the higher prediction accuracy and universality of the proposed forecasting method.
Online: September 26,2021 DOI: 10.7500/AEPS20210426004
Abstract:The offshore wind power grid-connected scheme based on diode rectifier (DR) can greatly reduce the investment cost, but the control and start-up problems are difficult to solve. The actively commutated current source converter (CSC) has the high power density and great control performance, but the cost is relatively high. This paper proposes a hybrid cascaded DC grid-connected transmission system for offshore wind power based on the DR and auxiliary CSC, which can realize the lightweight of offshore platform and solve the control and start-up problems of DR. First, the topology and mathematical model are analyzed. Then, the steady-state control strategy and black start control strategy are proposed for the offshore wind grid-connected system, and the simulation verification is performed based on PSCAD/EMTDC. Finally, the economic analysis of the proposed scheme is carried out. The results show that the hybrid cascaded offshore wind grid-connected system can smoothly complete the black start of wind farms, has good steady-state characteristics, and can adapt to the fluctuations of wind power output.
Online: September 22,2021 DOI: 10.7500/AEPS20210419001
Abstract:Offshore wind power has promising development potential, and reliable and efficient large-scale distant offshore wind power grid integration system is the key technology to develop the offshore wind power. Aiming at the miniaturization problem of offshore platform for distant offshore wind power HVDC transmission system, an HVDC transmission scheme for the grid-following medium-frequency distant offshore wind farm is proposed. This scheme utilizes the grid-following wind turbines, where the modular multilevel converters (MMCs) are installed at both the rectifier side and the inverter side of HVDC system. Firstly, the grid-following medium-frequency scheme is described from two aspects of topology and control system. Then, the influence of the offshore AC system operation frequency on the offshore wind farm and its HVDC transmission system is analyzed, including influence on the transformer, the AC cable and the MMC. Based on a ±320 kV/1 000 MW offshore wind power HVDC transmission system, the technical and economic efficiency of the proposed 100 Hz grid-following medium-frequency scheme is analyzed, including the main circuit parameters of key electrical equipment, the cost of AC cable, the cost of offshore platform, the cost of wind turbines, the AC cable loss and rectifier station valve loss, and the transmission capability of AC cable. Finally, an electromagnetic transient simulation model of the grid-following medium-frequency scheme is built in PSCAD/EMTDC to verify the effectiveness of the scheme.