The structure and operational mechanism of VSC-HVDC (Voltage Source Converter-High Voltage Direct Current) system based on MMC(Modular Multilevel Converter) connecting with passive networks are introduced and the mathematical model of MMC is given. The strategy of direct voltage control to guarantee the quality of power supply is proposed for the passive inverter of MMC,which controls the amplitude of AC-bus voltage by the feed-through of reference and the negative feedback of PI compensation, and maintains the nominal system frequency by the given modulation signal frequency. A MMC-based VSC-HVDC system for passive networks is established in PSCAD/EMTDC and different operational conditions are simulated,such as the variation of active and reactive power loads,AC voltage adjustment,etc. Simulative results show that high-quality power supply for passive networks is achieved by the proposed control strategy.%介绍了向无源网络供电的模块化多电平换流器(MMC)型电压源换流器型高压直流输电(VSC-HVDC)的系统结构和工作原理,引入了MMC的数学模型.提出了MMC无源逆变的直接电压控制策略,其中电压幅值控制由参考信号的直馈和负反馈PI补偿来实现,频率控制通过给定调制信号频率来实现,保证了良好的供电质量.在PSCAD/EMTDC中搭建了向无源网络供电的MMC型VSC-HVDC仿真系统,对有功和无功负荷变化以及交流电压降低等工况进行了仿真研究.仿真结果表明所设计的无源逆变控制器可以向无源网络提供高质量的电能.
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