An improved control strategy for DFIG system and dynamic voltage restorer under grid voltage dip

With the increasing percentage of wind power in the utility grid, grid codes require that wind turbines must have low voltage ride through (LVRT) capability. Considering that doubly fed induction generation (DFIG) systems have the tolerance capability, to overcome the drawback of LVRT operation of DFIG system using crowbar, a dynamic voltage restorer (DVR) is connected to the stator side to prevent the stator voltage fast changing, and then the rotor side converter (RSC) can be in normal operation. A mathematical model of the rotor voltage of DFIG during a symmetrical voltage dip is presented to describe the allowable changing rate of the stator voltage. A new connection structure of DVR is proposed where DVR and GSC share a DC capacitor. Based on the coordinated control of the DFIG system and DVR, the active power regulation and reactive power compensation can be implemented under the grid fault. The simulation results for a 1.5MW DFIG system is given to show the effectiveness of the proposed protection compared to the rotor crowbar during grid fault.