A control strategy combining sliding mode controller with crowbar circuit for low voltage ride through of direct-drive wind power system

The DC bus voltage is the main criteria to reflect whether the converter system is working properly or not. When grid voltage drops, the stability control of the DC bus voltage is the key to ensure that wind power generators not take off the grid. This paper had done a research on direct-drive wind power system and proposed a coordinated control method combining the crowbar circuit with sliding mode control. The crowbar circuit was linked with DC bus. A sliding mode controller replaced to the traditional PI controller and was implemented in the inner current loop of the motor-side converter. When the grid voltage dropped, the extra energy of the DC bus could be unleashed by crowbar circuit. Due to good rapid performance of controller, the output power of motor-side converter could be controlled by the sliding mode variable structure controller. At the same time, the DC bus voltage kept stability for rapid balance of energy. Simulation Results based on Matlab/Simulink show that this control strategy can not only improve the stability and dynamic response performance of the DC-bus voltage, but also effectively maintain the output power of generator and raise the ability of wind power system riding through the grid fault.