A new control strategy of DFIG-based wind turbines under unbalanced grid voltage conditions

This paper analyzes the effects of two control strategies on doubly-fed induction generator (DFIG) based wind turbine under unbalanced voltage then a new control strategy is proposed to achieve more advanced performance of it. In these control strategies, the rotor side converter (RSC) and grid side converter (GSC) are controlled in two positive and negative ((dq)⁺ and (dq)^-) reference frames so that the control of them in the (dq)⁺ frame is similar to what occurs in the balanced conditions. In two first control strategies, the RSC is controlled in the (dq)^- frame to eliminate the electromagnetic torque oscillations. In the first one, the GSC is controlled in the (dq)^- frame to balance the total output currents while in the second one, the GSC is controlled to eliminate the oscillations of the total active power generated by the DFIG system. In the proposed control strategy, the RSC is controlled in the (dq)^- frame to balance the stator currents; therefore the control of the GSC for eliminating the oscillations of the total active power is done easily. The simulation results obtained for a 7.5 KW DFIG based wind turbine validate the proposed control strategy and show the enhanced system operation during unbalanced voltage network.