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九开关变换器(nine-switch converter,NSC)可通过分时调制输出两组独立的三相电压,因此可用于代替双馈风电系统中的背靠背变换器.该文对NSC双馈风电系统的控制策略进行优化设计,通过对NSC直流母线电压的实时动态分配,使得一套控制策略可同时适用于电网电压正常与跌落两种工况.电网电压正常时,较高的直流电压可自动分配给网侧支路,以匹配较高的电网电压;当电网电压跌落时,较高的直流电压又可自动地分配给转子侧支路,以匹配转子较高的反电动势.该自动分配思路使得NSC系统在不增加辅助电路的前提下,即可实现低电压穿越,充分发挥了NSC的优点;同时还避免了不同控制策略的切换与电压跌落时刻的检测,大幅减少了系统设计的复杂度.“,”Nine-switch converters (NSC) can provide two sets of independent three-phase outputs by using the time-shared modulation,and thus can be utilized to replace the traditional back-to-back converters in the doubly-fed induction generation (DFIG) wind power system.This paper proposed an optimal control strategy design for the NSC-based DFIG system by introducing the real-time dynamic de-link voltage assignment,with which one set of control strategies can be effective under both normal grid-voltage and grid-dip conditions.With the proposed design,high dc-link voltage of NSC in normal grid condition was automatically assigned to the grid-side to match the high grid voltage;and high dc-link voltage when the grid dips was automatically assigned to the rotor-side to match the rotor's overshoot voltage.Such an automatic assignment makes the NSC-based DFIG system can achieve low-voltage-ride-through (LVRT) without extra auxiliary crowbar circuits,and thus fully use the advantages of NSC;such an automatic assignment can also avoid the mode-switching between different control strategies and the detection of grid-dip moment,and thus can greatly reduce the system complication.