| In recent years,with the increasing proportion of wind power generation in the power grid,the impact of wind turbines on the power grid has become increasingly apparent.Because the wind turbine is running in the maximum power tracking mode and decoupled from the power grid through power electronic converters,the output power of the wind turbine cannot respond to changes in the frequency of the grid,which causes the system’s inertia and frequency stability to weaken.Based on the analysis of the existing frequency regulation strategies,this thesis proposes a method for wind power generation system and energy storage system to participate in power system frequency regulation,which improves the frequency stability of grid-connected wind power and verifies it by simulation.Firstly,The thesis analyzes the problem of weakening the system inertia in the power grid with wind power generation,introduces wind power generation technology and energy storage technology,and summarizes the current state of frequency modulation of various wind power generation systems and energy storage systems,as well as their advantages and disadvantages.Secondly,the thesis analyzes the structure and working principle of the permanent magnet wind power generation system,and establishes models of each part of the system.This thesis introduces the principle of maximum power tracking for wind turbines,and MPPT control of wind turbines based on the optimal torque curve.In this thesis,the model of generator-side converter and grid-side converter are established,and their control systems are analyzed.Thirdly,the thesis studies the influence of wind power generation system on the primary frequency regulation and inertial response of the power system,and expounds the inertia control strategy based on frequency response,which can virtually simulate the inertia of conventional synchronous generators.For the contradiction between traditional virtual inertia control and maximum power control,a stepwise inertia control based on the optimal torque curve(OTC)is proposed.The thesis expounds the control process and principle of stepwise inertial control and the control strategies of each stage.Then,the thesis analyzes the power shortage caused by the load shedding phase in the stepwise inertia control,and selects a hybrid system of wind power generation and energy storage that is directly connected to the grid.A lithium battery and converter model of the energy storage system is constructed,and a control system for the energy storage converter is designed.During the load reduction operation phase of the wind power generation system,the thesis designs a frequency support control strategy for the battery-assisted wind power generation system,and describes the coordinated control process of the hybrid system of wind power generation and energy storage.Finally,the thesis builds a hybrid system model of wind power generation and energy storage under MATLAB/Simulink environment.The wind turbine operates safely under a stepwise inertia control strategy.The effectiveness of stepwise inertia control based on OTC is verified by analyzing the frequency and grid-side electrical quantities in a hybrid system of wind power and energy storage.The beneficial effect of lithium battery energy storage system in assisting wind power generation to participate in frequency adjustment in stepwise inertia control is verified. |
