For solving the problem that the unbalanced high voltage of the power grid easily leads to off grid accidents of direct-drive permanent magnet wind turbine，the optimal strategy in combination of sliding mode control，virtual synchronous generator technology and the positive and negative sequence voltage and current double closed-loop PWM control is proposed. By decoupling the positive and negative sequences of the grid-side voltage and current in the dq coordinate system，the relationship between the sequential component current and power under asymmetrical faults is set up，the command values of the positive and negative sequence currents is obtained by calculation，the active power is controlled to reduce the frequency fluctuation of the system，and the reactive power is regulated to support the voltage recovery at the grid-connected point. The output of the current inner-loop is taken as the input to the part of the voltage outer-loop control，the inner-loop PI control of the current is optimized into sliding-mode control so to enhance stability of the grid-connected inverter. The simulation experiment shows the effectiveness of the optimized control method. The fault ride through ability and operation stability of the permanent magnet direct drive wind power grid connected system in case of unbalanced high voltage are improved.