Research On Stability Of Microgrid/weak-grid Under Fault Doubly-fed Induction Generator

With the increasing permeability of doubly fed wind generation,it brings economical profits,also threatens the stable operation of the power system.For one thing,the dreadful operation conditions of doubly fed induction generator(DFIG)leads to high failure rate,stator winding inter-turn short circuit(SWITSC)is a common,high-risk fault,and the maintenance is very difficult,it accounts for more than 30% of motor failures.For another,wind power is larger in microgrid/weak-grid,integration voltage and frequency are sensitive to changing wind power,power mutation caused by SWITSC fault leads to the fluctuation of voltage and frequency,which will affect small signal stability of the system.This subject is established based on the above two aspects,and the main research work are as follows:(1)A small signal model of microgrid composed of fault DFIG unit,photovoltaic system,large-capacity energy storage and corresponding control strategies,network,load is deduced,and the simulation model is estabilished in MATLAB/Simulink.The mathematical model of DFIG with SWITSC is analyzed emphatically.(2)According to the Lyapunov theory,the eigenvalues and participation factors of the small signal model of wind-solar-storage microgrid system are obtained,the influences of SWITSC fault degree,light intensity,wind speed and control parameters on the stability of microgrid are studied through eigenvalue analysis.The correctness of the stability analysis theory is verified by simulation examples.(3)In the light of analysis conclusion of the participation factors in microgrid,a small signal model of weak-grid system consisting of fault DFIG unit and a synchronous generator is established based on the dynamic characteristics of the rotating mass of wind turbine.The integrated inertial frequency control is added on the basis of traditional control of DFIG to adjust frequency,and influences of frequency control strategies and the SWITSC fault on the frequency stability of the weak-grid are studied.(4)In order to solve the problem of voltage drop and frequency fluctuation caused by SWITSC,the voltage and frequency control schemes are proposed.A reactive po wer coordination control method of DFIG is adopted to raise integration voltage,improving voltage stability of weak-grid system;frequency fluctuation is reduced by adding droop control,improving frequency stability of weak-grid system.The effectiveness and feasibility of voltage and frequency control strategies is verified by simulation.