Improved control strategy of direct-driven permanent magnet synchronous generator for wind turbine under unbalanced grid faults

An improved unbalanced grid fault ride-through control strategy is proposed to meet the low voltage ride through(LVRT) requirements based on the analysis of power characteristics of a full rated converter for direct-driven permanent magnet synchronous generator(PMSG).According to the power characteristics,the relationship among dc-link capacitor voltage,power absorbed by interface reactors and grid-side power output is studied.The information of grid voltage drops is introduced into generator-side converter control to achieve coordinated control of grid-side converter and generator-side converter.The soft control strategy on dc-link capacitor voltage is adopted to suppress double-frequency active power ripple at the expense of a certain voltage fluctuations which is still within the safety range.The simulation results demonstrate that the proposed control strategy can enhance direct-driven PMSG's unbalanced grid faults ride-through capability.