2017, 41(9):58-64. DOI: 10.7500/AEPS20161017009
Abstract:An improved Monte Carlo sampling method called probability circle sampling based on the distributed generation probability model is presented. The power supply capability indexes of DC power distribution network were constructed and the multi objective function of the DC power supply capacity is proposed. The Delphi method and judgment matrix are used to analyze the index qualitatively and quantitatively prior to finally optimizing the solution with an improved genetic algorithm. In the calculation example, the DC distribution network of radial type, ring type and mesh type are calculated and compared at different permeability rates of DG. The feasibility of the proposed method is verified and considered useful as a reference for research on power supply capability of DC distribution network in the future.
2017, 41(23):15-21. DOI: 10.7500/AEPS20170616008
Abstract:The optimal allocation of DC circuit breakers is of great significance in improving the reliability of DC distribution network and reducing outage cost. Based on the minimum-cut set, a DC load area division method is proposed, and then an outage cost calculation model considering function failure of power electronic devices is established. As the DC circuit breaker will be cheaper with the development of electronic technology, a DC circuit breaker optimization dynamic programming(DP)considering the changing price of the breaker is proposed, in which the sum of switch investment, operating cost and outage cost is designed as the optimization objective, the number and location combination of DC circuit breaker are designed as the stage and the state of DP. By taking a loop distribution network as an example, the method proposed can divide the DC circuit breaker price into several intervals and get optimal allocation schemes of different intervals.
2017, 41(8):116-124. DOI: 10.7500/AEPS20160729015
Abstract:A DC distribution network using voltage droop control strategy has good stability, but the ability to adjust the high frequency random power fluctuations is poor. Being suitable for the voltage droop control of DC distribution network, a virtual inertia control method is studied to accommodate the rapidity and stability of the regulator, and to improve the quality of the DC voltage. The control strategy can compensate for the system power shortage by the rapid adjustment of battery's charging and discharging rate, which is caused by the change in the battery's droop coefficient. Thus this control strategy can provide a virtual capacitance much larger than the actual capacitance at the DC side and improve the system inertia. At the same time, the theoretical analysis of the specific virtual inertia margin under different operating conditions is provided, so that the control strategy can adjust the droop coefficient on the basis of the allowed swing range adaptively, allowing the battery to provide variable inertia support in accordance with its virtual inertia margin. This ensures the full and rational use of the inertia margin. In order to verify the effectiveness of the proposed control strategy, a four-terminal wind-battery-based DC distribution network is established in MATLAB/Simulink. The results show that the proposed control strategy is able to improve the system's transient response, improve the quality of DC bus voltage, and smooth the power fluctuation between the AC grid and DC grid. This work is supported by National High Technology Research and Development Program of China(863 Program)(No. 2015AA050101).
2017, 41(11):85-91. DOI: 10.7500/AEPS20160411007
Abstract:With the rapid development of DC distribution technology, distributed generation(DG)and energy storage system(ESS)can be integrated with distribution networks more efficiently, and a hybrid AC/DC topology configuration may appear. This paper presents the security-constrained coordinated economical dispatch method of energy storage systems and converter stations for hybrid AC/DC distribution networks. By optimizing reactive power adjustment of the converter station and charging/discharging of ESS, power supply companies can ensure safe operation of distribution networks while minimizing the total cost of energy purchased from the upper grid on the transmission and distribution separated electricity market. In addition, this is a mixed integer nonlinear programming problem and is difficult to solve. In this paper, the original model is transformed into a mixed integer linear programming problem by linearization technique. Finally, the simulation results can demonstrate the effectiveness and rapidity of the proposed method.
2018, 42(6):106-112. DOI: 10.7500/AEPS20170614011
Abstract:Firstly, a typical topology structure and node classification of flexible DC distribution network(FDCDN)are described. Secondly, a hierarchical coordinated control architecture for FDCDN is proposed. The system-level control adopts elite strategy based non-dominated sorting genetic algorithm with the embedded probabilistic load flow and the converter-level control uses multi-stage DC voltage margin control. The source-load-level control adopts the “quasi-cocktail” source-load response strategy to minimize the terminal power control error. Finally, a simulation model of FDCDN is established on the RTDS&dSPACE combined simulation platform. The effectiveness of the proposed hierarchical coordinated control strategy is proved by simulation.
2017, 41(24):184-192. DOI: 10.7500/AEPS20170609003
Abstract:The future distribution system will have the significant characteristics such as high density integration of distributed generations, interconnection of AC/DC hybrid system. Therefore, the fault analysis for distribution system will face new challenges. As the integration of high density distributed generation and power electronic equipments, the fault response presents the property of nonlinear temporal-spatial correlation, and the fault response interaction influences between AC/DC system further increase the difficulty of fault analysis. In this paper, the current research status of the distribution system fault analysis is summarized, and the key issues to be studied in the future are proposed including the analysis and decoupling modeling of distributed generations for the temporal-spatial correlation characteristics, the equivalent modeling of AC/DC hybrid distribution system, and the effective convergence algorithm.
2019, 43(3):205-215. DOI: 10.7500/AEPS20180508006
Abstract:Direct current (DC) power grid is effective in solving the problems when high penetration of renewable energy is integrated into the power system. However, the construction of the DC power grid will face challenges in the aspects of technology, equipment and standards. Based on the technical characteristics of DC power grid, three typical application scenarios such as high-penetration renewable energy grid connection, offshore wind power grid connection and DC distribution network are analyzed. The latest research progress of key technologies and core equipments of DC power grids is elaborated. The development direction of DC power grid technology is proposed. The key technologies for the development of DC power grids are analyzed. The future development of DC power grid basic theory system, breakthrough in key technologies and core equipment are pointed out. The above research indicates that DC power grid technology will play a greater role in the global interconnected energy network.