Improved dual-PI rotor current control scheme for a wind-driven DFIG during asymmetrical grid voltage dips

Large transient grid voltage unbalance will result in deterioration of the doubly-fed induction generators(DFIGs) by introducing over current of rotor side converter(RSC) and double frequency oscillation in dc link voltage and electromagnetic torque. The rotor current controller with the conventional reduced DFIG model, which does not take into account the stator flux transients, could not obtain good performance during the large transients. This paper presents an improved rotor current control scheme for a DFIG system suitable for studying conditions with transient grid voltage unbalance. The model designed takes into account the stator flux transients and provides complete decoupling control, mainly introduced in the rotor voltage equation. To verify the correctness and effectiveness of the new control design, simulated results on a 1.5 MW practical DFIG-based wind power generation system are presented and compared with those using the conventional dual PI rotor current scheme.