Research On Control Strategy Of Large Scale Wind Farm Participating In Power System Frequency Regulation

There are two factors of wind power which influence the stability of grid frequency in a bad way. One of the factors is the fluctuation, and the other is that wind generator can not participate in frequency control. Based on the second factor, the frequency control strategy of large-scale wind power is studied in this paper.The operation characteristics of doubly fed induction generator (DFIG) and the frequency response characteristics of the power system are studied firstly. Then according to the frequency response curve of single generator system, the influence on frequency of injected DFIG is analyzed. The analysis result shows the equivalent inertia coefficient and the unit regulating power coefficient is lower after injected wind power into grid, and the effect is that the initial rate of frequency and frequency deviation of steady state is higher. Next an example of Zhejiang power grid with wind power is taken and the simulation results also verify the theoretical analysis conclusion, in addition, the frequency stability is worse with the increase of wind power penetration rate.According to the analysis of the frequency response of the power system, the frequency control strategy of DFIG is put forward which is designed to imitate the frequency modulation progress of synchronous generator. This control strategy uses virtual inertia control method to imitate the inertial response progress and droop control method to achieve the progress of primary frequency regulation. In order to improve the frequency regulation stability of DFIG. this control strategy uses over-speed control and pitch control to achieve de-loading operation. Based on the operation characteristics of DFIG under different wind speed, three wind speed range is designed to make this control strategy adaptable to speed. And an example is taken to show the effectiveness of this control strategy under different wind speed. The simulation results also show that the frequency modulation ability of DFIG is improved with the increase of wind speed.Considering the wake effects which make the difference operating conditions of DFIG in a wind farm, an equivalent model of wind farm with wake effects is conducted.And considering the randomness of wind speed, an evaluation model, with probability distribution of wind speed, about the frequency control capacity of wind farm is put forward. And an example is taken to compare this method with the method of direct calculation, the result shows that the method studied in this paper is a little conservative,but it does consider the wake effect and random effects in wind farm, so this method is more accurate in reflecting the capacity of frequency regulation.