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Doubly fed induction generator (DFIG) based wind turbines have been found to be very sensitive to asymmetrical grid fault, wherein the harmful oscillations in the electromagnetic torque has being made a big concern. What makes things harder is that latest grid codes require grid-connected wind turbines to possess the ability of positive-and negative-sequence reactive current supporting. Hence, it becomes a guide mechanism to meet the grid codes and to ensure the operation safety of the wind turbines. Even though a tradeoff could be made between them, it is still quite difficult to coordinate the current dispatch of the DFIG's rotor-and grid-side converters (RSC and GSC), since there are totally eight currents needing to be carefully designed, i.e., the positive-and negative-sequence active and reactive currents in each converter. To address this issue, this paper analyzes the reactive current constraints in detail, based on which a coordinated reactive current control strategy is put forward for the DFIG-based wind turbines during asymmetrical grid condition. Simulation studies demonstrate the effectiveness of the proposed strategy. INDEX TERMS Doubly fed induction generator (DFIG), wind turbine, asymmetrical grid, reactive current support, fault ride-through (FRT).

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