Control and Protection of a DFIG-Based Wind Turbine under Unbalanced Grid Voltage Dips

This paper proposes a new direct power control (DPC) strategy and a novel crowbar protection technique for the doubly fed induction generator (DFIG) used in the wind power generation systems. The main difficulty for a DFIG to ride through severe unbalanced grid voltage dips is the large transient currents induced in the rotor windings, which may damage the ac excitation converter. The proposed DPC is capable of suppressing the transient oscillations of fault currents and electromagnetic torque. The crowbar protection is able to limit the peak values of the fault rotor currents under a preset threshold. Simulation results of a 2MW DFIG system prove that with this control scheme the DFIG is capable of riding through the severe unbalanced grid voltage dips.