In the case of asymmetric faults in the power grid, the DC voltage of direct-driven wind power system rises with double frequency fluctuation. The cause of the phenomenon is analyzed and a comprehensive low-voltage ride-through control strategy is proposed. The dual current-loop control structure is adopted on the grid side to reduce the distortion of the current at point of common coupling. The control structure based on the Quasi-PR controller is adopted on the generator side to let electromagnetic power of PMSG follow the active power outputted by the grid-side inverter, thereby reducing the difference of active power between two sides of the converter and suppressing rise and double frequency fluctuation of DC voltage.

Asymmetric fault; Direct-driven wind power system; Fluctuation of capacitor’s voltage; Low-voltage ride-through