In order to decreasing the switching frequency of modular multilevel converter (MMC) , a novel unified power-flow controller (UPFC) topology was presented based on MMC. A reduced switching-frequency phase-shifted pulse-width modulation(PWM) scheme including voltage balancing strategy was described for the operation of the proposed MMC-based UPFC, and the circulating current suppressing method was discussed through analysis of circulating current in MMC. The reported lime-domain simulation results show that the proposed circulating current suppressing control strategy can greatly decrease harmonic component in arm current and voltage rippers of capacitor without increasing arm inductance. This topological structure has characteristics of high modularization, good reliability, conrenient maintenance and so on.%为了降低模块化多电平换流器的开关频率,提出了基于模块化多电平(MMC)技术的新型统一潮流控制器(UPFC)的拓扑结构,将调制技术与子模块电容电压均压技术相结合,提出了一种可有效减低开关频率的脉宽调制方法.在对模块化多电平换流器环流问题分析基础上,提出了环流抑制控制器的设计思路.仿真结果表明,该控制器可在不增加桥臂电抗的前提下减少桥臂电流中的谐波成分,提高波形质量,同时降低各子模块电容电压波动,具有一定的工程意义；该拓扑结构具有模块化程度高、可靠性好、便于维护及容量拓展等特点,是一种极具发展潜力的拓扑结构.
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