Research On Low Voltage Ride Through Fordouble Fed Induction Generator

How to develop and utilize renewable resource has become a crucial problem,which concerns the fundamental benefits of the people all over the world.Wind power plants proportion rises in power grid system by years,as a result,the standards of wind power plant grid connection become increasingly strict to keep the wind turbines from operating when grid failures occur.Therefore,the research on high and low voltage ride through of wind power system is of great significance.This thesis based on doubly-fed induction generator(DFIG)is aimed at discussing how to improve the low voltage ride through capability and researching the solutions by using MATLAB as simulation platform.Firstly,introducing the inner structure,woring principle and the function of each part of DFIG.Establishing the mathematical model of each part of DFIG and introducing the concept of low voltage ride through.Elaborating and analysing the reason for rotor side overcurret and DC bus side overvoltage generated by fan system in low voltage ride through process.Then establishing vector control strategy for double PMW converter and export the control block diagram by establishing rotor side converter and grid side converter on d-q axis.Secondly,further reserch for protection circuit resistance optimization of rotor side Crowbar and protection circuit unloading resistance value range DC bus side Chopper by deducing formula when voltage drops severely.According to the current standards of wind power plant grid connection,wind power plants must provide dynamic reactive power compensation by the strategy of Static Synchronous Compensator and Thyristor Switched Capacitor working together to improve low voltage ride through capacity.At last,Three protection solutions are designed for low voltage ride through.The first solution is inserting Crowbar protection circuit.The second solution is inserting Crowbar protection circuit and Chopper circuit.The third solution is inserting Crowbar circuit,Chopper circuit and hybrid reactive power compensation device.By conducting MATLAB simulation experiment,comparing rotor side overcurret value and DC bus side overvoltage value and take whether reactive power dynamic support can be provided effectively when voltage drops as the standard.The result shows that the third solution is the most effective one as it restrains system overcurrent and overvoltage better,besides,it provides reactive power compensation for the grid.