Optimal control strategy for PMSG wind power system to restrain the oscillation of DC voltage and transmission power under asymmetrical grid fault

In order to improve the fault tolerant capability for direct-driven wind power system under asymmetric grid faults, an optimal integrated control strategy is proposed in this paper. Based on mathematical model of grid-side converter in rotating reference frame, the double base frequency voltage equation represented by second order harmonic components is decomposed through coordinate transformation. In the analysis of grid-side output power characteristics, positive and negative sequence components of grid-side voltage and current is calculated by being converted to the same reference frame and an additional compensation control loop for simultaneously suppressing the second harmonic components of active and reactive power is designed. Moreover, to reduce DC voltage swell during faults, mathematical model of DC-link voltage is analyzed and a feed-forward modified component is added to the traditional grid-side DC voltage control loop. According to synthesizing the two aspects improved control methods, this paper put forward an optimal control strategy to enhance the fault tolerant capability for direct-driven wind power system under asymmetrical grid faults. The effectiveness of the improved control strategy is verified by PSCAD/EMTDC simulation results.