Study on LVRT of DFIG Wind Power System Based on Crowbar Protection Circuit

The wind power system based on the Doubly-Fed Induction Generator (DFIG) is one of the most popular wind power systems considering the economy and performance. However, DFIG is extremely sensitive to the grid fluctuations or faults since its stator side connected directly to the grid. When the grid voltage drops heavily, hardware protection must be required to ensure the system ride through the low voltage stage. The Crowbar Protection Circuit (CPC) is most popularly used. This paper studies the transient process of the system when the grid voltage drops. And then, the crowbar resistance and the best CPC duration are optimized by the analytic expression of transient current on the rotor side based on the standard of Low Voltage Ride Through (LVRT). The results show that the optimal crowbar resistance and the right time to remove the CPC are relevant to the rotor current transient component and the time constant. Finally, the feasibility by using grid-side converter as a STATCOM to support the reactive power of the grid during the stage of crowbar protection is discussed. The results are simulated by MATLAB/Simulink and verifies the correctness of the theory analysis.