| As the important part of renewable energy power generation, wind power generation experienced dramatic development in the last two decades. As one of the main stream types of variable-speed constant-frequency wind power generation system, the direct-drive wind power generation system has enormous development potential, as it has the significant advantage of eliminating the gearbox. The generator in direct-drive wind power generation system is connected to the grid through the dual PWM full-scale power converter. There is a DC-link capacitor between the generator side converter and the grid side converter. The converter is the core of power conversion. The increased penetration of wind energy into the power system is likely to influence the operation of existing utility networks. In order to keep the safe operation of the power system, the wind turbines need to remain connected to the grid when a voltage dip is detected. So the low voltage ride-through capability of the wind turbines need to be enhanced. In the traditional control system, additional devices are needed in parallel of the DC-link, which increase the cost and is not good for heat dispersing, so an improved control strategy is proposed in this paper. The electromagnetic power of the PMSG is limited under the grid faults to minimize the power transferred to the DC-link capacitor, as the output power of the grid-side converter is reduced, so the stable control of the DC-link voltage is realized. MATLAB/Simulink tool box is employed to construct the simulation modules for the direct-drive wind power system, and the SVPWM modulation strategy which has high utilization factor is applied. Both control strategies are verified during the normal operating grid and grid faults, the traditional control strategy and the improved control strategy during grid faults are compared, the simulation result demonstrates that the improved control strategy has better low voltage ride-through capability. |
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