Fault ride through under unbalanced voltage sag of Wind Energy Conversion System using Superconducting Magnetic Energy Storage

With the increasing penetration of wind power, smoothing power fluctuations and enhancing performances of fault ride-through of Wind Energy Conversion System (WECS) are two urgent issues needed to be addressed. Superconducting Magnetic Energy Storage (SMES) is adopted to auxiliary smooth the fluctuation of wind power and absorb the excess energy when grid voltage fault happens, thus stabilizing the DC bus voltage and balancing the output and input power. As for the LVRT control strategy, compared with the traditional PI control which the AC output signal cannot be tracked with zero steady-state error, Quasi Proportion Resonant Differential (QPRD) Control is proposed in this paper. Through designing the gain of the resonant point to infinite, the tracking performance of AC signal realizes zero steady-state error, and the overshoot and settling time is reduced. With the application of the proposed QPRD control in doubly-fed induction generator (DFIG) type WECS with SMES, not only negative sequence current is inhibited, but also the double-frequency oscillation in active power and DC bus voltage is suppressed .The feasibility and effectiveness of the proposed QPRD control for 1MW DFIG type WECS with SMES are verified through MATLAB/Simulink simulation.