Research Of Coordinated Control Strategy For Voltage And Reactive Power In Wind Power Grid Booster Station

Wind power generation has a series of advantages such as cleanliness, non-pollution, renewability and so on. With its rapid development in recent years, wind power has played an important role in our energy structure. With China’s increasing exploiting of renewable resources and new energy, the strategic position of wind power in the thirteenth Five-year Plan will be further enhanced. In the foreseeable future, wind power will usher in a golden period of rapid development. Meanwhile, because wind power has strong randomness and fluctuation, the access of large-scale wind farms to the grid has also brought some puzzles such as power peaking, power quality, which also has brought some challenges to the safety and stable operation of the power system.Especially in recent years, with the continuous expansion of the capacity of wind turbines and wind farm size, also with the formation of numbers of million-kilowatt wind power base, the influence of grid-connected wind power on the stability of power system has become even more significant. As most of the planned wind power base located in economically underdeveloped areas of china, in the end of the grid, and their connection with grid is weak, therefore, the problem of grid stability caused by them is more serious. Consequently, researchers should propose some practical solutions to meet the needs of large-scale wind power base for voltage stability.Based on the current development situation and the existing problems of wind power and relying on the project "Research on Reactive Power Compensation Device as Well as Control Strategy in 500KV Wind Power Grid Booster Station" carried out by China EPRI Science & Technology CO., LTD., this paper conducted a research on Coordinated Control Strategy for Voltage and Reactive Power in Wind Power Grid Booster Station, and proposed a control strategy used for SVG of chain H bridge structure.Firstly, the principle and performance of reactive power compensation equipment in wind farm are analysed and SVG is determined to be used as the dynamic reactive power compensation device of booster stations. Then different topology structures used in main circuit of SVG are analysed and compared and cascade H bridge topology is chosen to be the main circuit of SVG in this work. And according to the needs of actual grid system, we designed the capacity and element parameters of SVG.Secondly, we analysed the control strategy of the SVG device, including PWM modulation technology, DC voltage control technology, etc., and we put forward a novel current control strategy used for SVG:the unified decoupling current control and current split phase correction method, which can solve the problem of unbalanced current in three phases and improve the accuracy of adjustment. In addition, according to the scale of wind farm group and considering the actual reactive demand of grid-connected system, in this paper, we proposed a control strategy based on SVG and shunt capacitor bank to satisfy the reactive voltage requirements of wind power grid system under all kinds of conditions.Finally, this paper built a simulation model based on RTDS platform to simulate the dynamic compensation performance of SVG:the response speed and precision in the system under steady state operation. Then the running states of SVG when t the output voltage jitters or contains various harmonics are stimulated to verify SVG’s performance of anti-interference. Furthermore, this paper simulated the transient compensation performance of SVG when single phase short circuit, two-phase short circuit and three-phase short circuit occur in the interconnected system. And we analysed SVG’s capability of supporting the system voltage as well as the transient stability, to verify the correctness of the methods and strategy we proposed.The main work done in this paper focused on the voltage and reactive power control of wind power grid booster station. This work provides technical reference to the construction and operation of tens of millions of kilowatt wind power base, as well as enhancing the safety and stability of grid-connected wind power system. Meanwhile it has vital significance in theory and practice.