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With a high proportion of wind power being transmitted through ac and dc lines, a new power grid pattern has gradually emerged. A dc inverter is prone to commutation failure, which may lead to cascading trip of ac lines for overload, resulting in serious consequences. However, existing control methods have problems of over-or under-shedding and are unsuitable for high-proportion wind power transmission systems. Accordingly, a new fault overload control method based on emergency acceleration of doubly fed induction generator (DFIG) is proposed. The fast power control capability of DFIG is fully utilized; the active power of power grid could be rapidly balanced. First, the fault characteristics of a wind power ac/dc transmission system under the fault of dc receiving-end grid are analyzed, and the power flow transfer after self-recovery from the dc commutation failure is derived. Second, by analyzing the power characteristics of DFIG, a fault overload control idea of the wind power transmission system is proposed based on emergency acceleration of DFIG. At last, the maximum controllable capacity of a wind farm is analyzed, and a fault overload control strategy of the wind power transmission system is proposed. The simulation results prove that the proposed method can rapidly reduce the output of wind farms and prevent the overload of ac lines. INDEX TERMS AC/DC system, DFIG-based wind farm, power flow transfer, cascading trip, emergency power control. I. INTRODUCTION Wind energy resources and load centers are reversely distributed. Wind power development generally adopts the mode of large-scale centralized development and long-distance high-voltage transmission [1]. Wind power transmission through line-commutated converter based highvoltage direct current (LCC-HVDC) has become the main method of cross-zone allocation for wind energy resources because LCC-HVDC transmission system has a large transmission capacity and long transmission distance. The associate editor coordinating the review of this manuscript and approving it for publication was Datong Liu.

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