Improved Direct Power Control of a DFIG-Based Wind Turbine During Network Unbalance

This paper proposes an improved coordinate direct power control (DPC) strategy for the doubly fed induction generator (DFIG) and the grid side converter (GSC) of a wind power generation system under unbalanced network conditions. Two improved DPC schemes for the DFIG and the GSC are presented, respectively. The DPC for DFIG is to eliminate the torque and stator reactive power pulsations, while the DPC for GSC is to compensate for the pulsations of stator active power. In order to provide enhanced control performance of the overall system, the resonant controllers tuned at the fundamental and double grid frequency are applied in the improved DPC to eliminate the torque and power pulsations produced by the transient unbalanced grid faults, so that the output power of DFIG and GSC can be directly regulated without any necessity of the positive and negative sequence decomposition. The effectiveness of the proposed DPC strategy is verified by the simulation results of a 2-MW DFIG system under unbalanced grid voltage conditions.