Active and Reactive Power Control of Doubly Fed Induction Generators for Wind Energy Generation under Unbalanced Grid Voltage Conditions

This article presents a direct power control design of a wind turbine driven doubly fed induction generators under unbalanced network voltage conditions. A coordinate control strategy for the rotor-side converter and grid-side converter is proposed. The rotor-side converter is controlled based on the direct power control principle to eliminate the electromagnetic torque oscillations at a double supply frequency under unbalanced grid voltage. The grid-side converter is controlled to regulate the DC-link voltage and to cancel the pulsations in the total output active or reactive powers. The proposed control scheme removes both rotor current regulators and decomposition processing of positive- and negative-sequence rotor or grid currents. Simulation works are carried out to confirm the validity of the proposed scheme during unbalanced voltage supply. The performance of the proposed direct power control scheme is analyzed and compared with an improved vector control during grid voltage transients. The results show that the proposed direct power control scheme reduces the double frequency oscillations in the total and grid-side converter active and reactive powers, electromagnetic torque, and DC-link voltage.