An Optimized Voltage Support Strategy for PMSG-Based Wind Turbines under Unbalanced Grid Fault

Reactive power is normally injected into grid to support voltages under unbalanced grid fault. However, the non-fault phase voltage is increased with only positive sequence reactive power injection, and the degree of three-phase voltages unbalance is deepened. Therefore, it is necessary to inject negative sequence reactive power to suppress the rise of non-fault phase voltage. To address this problem, an optimized strategy based on second harmonic active-power suppress control (HAPSC) and voltage unbalance factor (VUF) is proposed. The main advantages of improved strategy are reducing the degree of three-phase voltages unbalance and supporting voltages. Simulation in PSCAD/EMTDC is used to verify the effectiveness of the proposed control strategy.