As the energy is distributed in each phase and bridge arm of the modular multilevel converter (MMC),it is accompanied by interphase circulating current while the converter is operating.The mathematical model of MMC is built,and the operation principles of the MMC are briefly analyzed.The mechanism of the converter arm oscillating current is found based on the analysis of the causes of the interphase circulating current and the resonance frequency of the converter.An oscillating current suppressing method based on virtual damping is designed,which suppresses oscillation by adding virtual damping to the output voltage reference of the converter arm.Finally,the effectiveness of the suppression method is verified both in the PSCAD/EMTDC simulation model and the 49-level low-voltage MMC prototype.%模块化多电平换流器(MMC)由于能量分布在各个相和桥臂中,导致工作过程中伴随着相间环流.建立了MMC拓扑的数学模型,分析了MMC拓扑的工作原理,通过对相间环流的形成原因和换流器自身谐振频率的分析,得出了桥臂电流振荡的形成机理.为抑制桥臂电流振荡,设计了基于虚拟阻尼的振荡抑制方法,通过在桥臂电压指令中加入虚拟阻尼分量抑制振荡.在PSCAD/EMTDC的仿真模型和49电平MMC低压样机上分别验证了虚拟阻尼电流抑制方法的有效性.
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