Research On Control Strategy Of Wind Turbine Combined With Energy Storage For Frequency Support

Under the current severe environmental and energy pressures,the effective use of new energy can help the power system achieve low-carbon transformation.Among them,wind power generation has achieved unprecedented development due to its mature technology and environmental friendliness.Wind power has the characteristics of volatility and unpredictability,and the wind turbine is decoupled from the system frequency or small in inertia through the grid connection of the power electronic converter.Therefore,access to the grid will not only increase the burden of the grid,but also weaken the grid.The inertial response capability of the conventional unit will be difficult to meet the frequency regulation demands of the grid under certain special conditions.With the additional control method,the wind power generator itself has the frequency regulation capability,which has become the development trend of wind power grid connection.At the same time,in recent years,the energy storage technology has developed rapidly,and it has become a high-quality frequency regulation resource because of its fast power adjustment speed,accurate power command tracking,flexible charging and discharging power adjustment and no climbing limit.The use of wind turbines,energy storage and conventional unit frequency regulation resources complement each other to construct a wind-fed joint frequency regulation method is one of the effective means to solve the problem of power system operation safety and stability caused by large-scale access to wind power.This paper studies the control method of wind storage combined frequency regulation.Firstly,systematically study the characteristics of wind power and the impact of wind power grid-connected on grid frequency stability.The van der Wein spectrum is used to analyze the distribution characteristics of wind speed in the frequency domain.According to the measured data of the measured data and load of the wind farm,statistical methods are used to analyze the wind power fluctuation characteristics,wind farm cluster effect and load power fluctuation characteristics.By comparing and analyzing the fluctuation characteristics of the equivalent load power and the actual load power after the wind power is connected to the grid on the short time scale of 5 minutes and 15 minutes,the influence law of wind power access on the grid climbing demand is summarized and revealed.Simulation model to quantitatively analyze the impact of wind power grid-connected on the grid frequency regulation system and power system frequency.Secondly,it analyzes the principle of conventional units and wind turbines participating in frequency regulation and constructs a grid frequency regulation simulation model.The wind turbine speed protection method considering speed feedback is proposed,and the wind turbine frequency output is adjusted in combination with the real-time feedback of the speed to prevent the sudden change of the wind turbine output and the speed limit.The speed recovery method considering the operating state of the system is proposed to improve the system frequency drop caused by the speed recovery;MATLAB/Simulink builds a simulation model for simulation experiments.The results show that the proposed speed protection and speed recovery method can effectively improve the frequency regulation effect and frequency regulation performance of wind turbines.Finally,on the basis of analyzing and explaining the principle that energy storage participates in frequency regulation,a method of energy storage force constraint considering the state of charge(SOC)of energy storage is proposed.Furthermore,under different wind speed conditions,according to the shortcomings of wind turbines participating in grid frequency regulation,a wind-fed joint frequency regulation control method considering wind turbine speed recovery demand is proposed and the inertia of wind storage system is analyzed.Based on the MATLAB/Simulink simulation model,the proposed control method is validated.The results show that the proposed method can provide effective frequency regulation support to the system in the full wind speed region,and alleviate the secondary frequency drop caused by the speed recovery.