This paper proposes an improved direct power control (DPC) strategy for a doubly fed induction generator (DFIG)-based wind power generation system under unbalanced grid voltage dips. The fundamental and double grid frequency power pulsations, which are produced by the transient unbalanced grid faults, are mathematically analyzed and accurately regulated. Five selectable control targets, with proper power references given, are designed for different applications during network unbalance. In order to provide enhanced control performance, two resonant controllers, which are tuned to have large gain at the power pulsation frequencies, are applied together with the proportional-integral controller to achieve full control of the DFIG output power. The effectiveness of the proposed DPC strategy is verified by the experimental results of a 5-kW DFIG system under different unbalanced voltage dips, which are generated by a specially designed voltage dip generator.Index Terms-Direct power control (DPC), doubly fed induction generator (DFIG), grid voltage unbalance, resonant controller, wind turbine.

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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. Index Terms-Direct power control, doubly fed induction generator, network unbalance, resonant controller, wind turbine.

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