Research On Control Strategy Of Large Scale Wind Power Participation In Power Grid Frequency Regulation Based On DFIG

As the environmental pollution and energy crisis in the world become more and more prominent,clean renewable wind energy resources are increasingly welcomed by all countries,and the capacity of wind power grid integration is increasing.However,the inverter-controlled wind turbines are usually decoupled from the system frequency and can not take part in the system frequency regulation actively,which reduces the frequency stability of the power grid and poses a great challenge to the safe and stable operation of the power grid,restricting the wind power acceptance capacity.Therefore,large-scale wind power involved in grid frequency regulation has become the current research focus.In order to enhance the frequency stability of the power grid,control methods such as rotor kinetic energy control,over-speed control and pitch control for improving the frequency response capability of wind power have been proposed one after another.However,the range of these strategies and the frequency regulation effect are different.How to coordinate the different control strategies to achieve the maximum utilization of the frequency regulation capability of the wind turbine is a key issue to be solved urgently.In addition,due to the complexity of the wind speed distribution in wind farms and wind power clusters,how to coordinate the distribution of active power output of each unit under complex operating conditions to give full play to the frequency regulation capability of wind farms is also the difficulty of wind power to participate in power grid frequency regulation.In view of the above problems,the control principle of these three control strategies is analyzed.The control characteristics of each control strategy are verified by simulation,and the control effects,scopes,advantages and disadvantages of each control strategy are clarified.Then,the applicable range of over-speed control is quantified,the over speed limited de-loading curve is derived and fitted,and a frequency regulation strategy for wind power based on limited over-speed de-loading curve partitioning is proposed.This strategy can adjust the cut-off point according to the level of de-loading and exert the advantages of rapid response of over-speed control,improve the inertia response of wind turbines at low wind speed,and avoid the mechanical wear caused by frequent changing pitch,which give full play to the frequency regulation capability of wind turbines.Finally,on the basis of the research on the frequency control strategy of the wind turbine unit,considering the influence of de-loading power on the frequency regulation characteristics of the wind turbine,a method of wind farm participating in the grid frequency regulation based on the coordinated distribution of de-loading power is proposed.Based on the combined control method of rotor kinetic energy control and de-loading control of a single wind turbine in wind farms,the method takes into account the differences in operating conditions of wind turbines,and uses the variable de-loading power coordinated distribution coefficient based the wind speed of wind turbines to distribute de-loading power,optimizing the frequency regulation capability of the wind farm.