The directly-driven variable speed constant frequency wind power generation system, which consists of the permanent magnet synchronous generator (PMSG), is connected to the grid by full size power converters. When severe faults occur in grid, the faults would not only cause serious damage to HVDC devices, but also have an adverse impact on the stable operation of overall wind power generation system. The disability mechanism of DC voltage during faults is analyzed. Based on the inertial energy storage characteristics of PMSG rotor and the reactive power compensation capability of grid-side converter, a novel coordinated control strategy aimed at improving the fault ride-through capability of PMSG is proposed. In order to decrease the imbalance power injected to the DC-link and suppress the overvoltage of DC-link, the proposed control strategy adopts an optimal generator-side segmented rotor speed controller to adjust the active power from wind turbine and increase the reactive power to grid on the basis of the grid-side converter with reactive power adjusting capability. A single-machine infinite-bus power system model in PSCAD/EMTDC is used to validate the effectiveness of the proposed control system for improving the fault ride-through capability of PMSG.