Crowbar Control Strategy for Doubly Fed Induction Generator of Wind Farm During Power Grid Voltage Dips

Due to the advantages of doubly fed induction generator(DFIG)such as controlling active and reactive power independently and smaller capacity of AC excitation converter is required;they are widely used in wind power generation systems.However,the smaller capacity of AC excitation converter restricts the control ability of DFIG set while disturbance occurs.To protect AC excitation converter,it is necessary to limit the high inrush rotor current and provide a bypass for it via a Crowbar connected to the rotor windings.In this paper,a novel Crowbar control strategy is proposed to limit the over current in the rotor and the over voltage of the DC bus as well as the transient oscillation of the electromagnetic torque. Moreover,a capacitive current is injected into the grid to assist the recovery of the grid voltage.Simulation results prove that with this control strategy the DFIG is able to ride through the more severe grid voltage dips;thereby the operation reliability of DFIG sets can be effectively improved.