Enhanced Control and Operation of DFIG-Based Wind Farms During Network Unbalance

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 “small” steady state and “large” transient unbalances.