Asymmetrical voltage dip ride-through enhancement of directly driven wind turbine with permanent magnet synchronous generator

The control strategy for directly driven wind turbine with permanent magnet synchronous generator (D-PMSG) was investigated to enhance its capability of low voltage ride through (LVRT). The positive and negative sequence components were detected by instantaneous symmetrical components method on grid voltage. Based on analyzing the impact of grid asymmetrical voltage dip on D-PMSG, the grid positive sequence voltage was introduced into the calculation of gen-side rectifier (GSR) reference power. A control strategy which reduced generator power according to the ratio of grid positive sequence and rated voltage was proposed, and a D-PMSG model connected to grid was established. The current feedforward control was applied to inner loop and the power control was used to outer loop, for GSR control. For grid-side inverter control, the negative sequence current was regulated at zero in inner loop and the DC voltage was stabilized in outer loop. Simulation results showed that during symmetrical and asymmetrical grid voltage dips, the proposed strategy could limit the inverter current, the DC-voltage and the mechanical rotational speed of the turbine. The LVRT capability of D-PMSG is improved through keeping the power balance of both the PMSG and the converter.