Modular multilevel converter(MMC)is widely used in the field of HVDC transmission,but its application in the medium voltage variable-speed motor driving system has the problem of the capacitor voltage fluctuations when the motor at low speed.Aiming at this problem,this paper designs a new hybrid MMC topology.Based on it,the medium voltage frequency converter can significantly reduce the capaci-tance voltage fluctuation,including the low speed condition.In addition,the new topology does not intro-duce common-mode voltage,so no insulation and bearing current problems,while the current stress in the entire speed range will remain within the limits,so the equipment is more efficient.Based on the working principle of the new hybrid topology,the related controller is designed.Finally,the prototype of the fre-quency converter is set up,and the test results verify the performance of the proposed new topology.%模块化多电平变换器(MMC)被广泛应用于高压直流输电领域,但其在中压变频调速系统中应用时存在电机低转速时电容电压波动较大的问题.针对该问题,本文设计了一种新型混合MMC拓扑结构,基于此设计的中压变频器能显著降低电容电压波动,尤其是在电机较低转速运行时.此外,新型拓扑不会引入共模电压,从而无绝缘和轴承电流问题,同时电流应力在整个转速范围内将保持在限值内,故设备效率较高.基于新型混合MMC拓扑的工作原理,设计了相关控制器.最后,搭建了变频器原理样机进行了相关试验,试验结果验证了所提出新型混合MMC拓扑的性能.
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