Study On Double-fed Wind Power Generation System Low Voltage Ride Through

Under an increasing conflict between resources and environment globally, new energyindustry is rapidly developing in recent years. The wind power generation technology has alsomade rapid progress. As wind turbine interconnection capacity proportion is rising, when thepower grid fails, wind turbines need to have the capability of low voltage ride through(LVRT). This paper focuses on the current mainstream of doubly-fed induction generator(DFIG) as the research object, and makes a deep study of wind turbines low-voltage responsecharacteristics in three-phase short-circuit fault.This article makes a detailed analysis on the three-phase symmetrical fault transientchange process of DFIG. On this basis, it analyses the effect of voltage drop on the rotor faultcurrents and DC bus. As the voltage drop to deepen, the fluctuation of DFIG internal electricparameters will be more severe. Amplitudes for different voltage drops, it should be taken theappropriate control strategy.In the case of grid voltage drop occurs a small value for DFIG the low voltage ridethrough, this paper uses stator the improved control strategy combine flux compensationexciting current change with suppression rotor current rotating component. This strategyconsiders the dynamic variation characteristics of DFIG voltage sag, and can suppress thestator and rotor transient current fluctuations. In the Matlab/Simulink, it simulates thedynamic response characteristics of DFIG units under different drop amplitude. Simulationresults show the improvement strategy can effectively reduce the impulse current amplitude,and will improve the low voltage through capability of DFIG.In the case of the large value of the voltage drop, this paper achieves low voltage faultcrossing of DFIG by adding the rotor side Crowbar circuit. It analyzes the impact of Crowbarresistance and switching time on low voltage across. From two angles of suppressing surgecurrent and DC bus over voltage appeared in the rotor circuit, it can propose the resistancereasonable value range from the formula. In the Crowbar switching time, it considersthe influence of DC voltage and rotor current instantaneous peak, and make a in-depthresearch on the removal of pre-fault, fault and fault clearing time after the end of the threeswitching time. Propose the control scheme based on Crowbar circuit of doubly fed windturbine. Simulation results Crowbar resistance and switching time by a reasonable choice,LVRT capability of doubly-fed wind turbines will have optimal effect.