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This paper investigates the control and operation of doubly fed induction generator (DFIG)-based wind generation systems under unbalanced voltage conditions. DFIG system behaviors under unbalanced voltage are analyzed and different control targets are discussed. A new rotor current control strategy containing a main controller and an auxiliary controller is proposed. The main controller is implemented in the positive (dq)+ frame without involving positive/negative sequence decomposition, whereas the auxiliary controller is implemented in the negative (dq)- frame with negative sequence current extracted. The impact of providing unbalanced control on converter voltage rating is investigated. Simulation results using EMTDC/PSCAD are presented for a 2-MW DFIG wind generation system to validate the proposed control scheme and to demonstrate the enhanced system operation during ldquosmallrdquo steady state and ldquolargerdquo transient unbalances.
Date of Publication: Dec. 2008