To maximumly protect the medium-voltage motor in a back-to-back medium-voltage motor driving system without transformer based on modular multilevel converter(MMC)from the influence of asymmetric grid faults and switching actions,a control strategy for minimizing the common-mode voltage of the front-end transformerless grid-connected MMC is designed.The common-mode voltage caused by the asymmetric grid fault can be canceled by the MMC counterpart voltage,and the switching ripples caused by the switching action of the MMC can be suppressed by arranging the arm-voltage pulses end-to-end.In addition,the influence of MMC common-mode voltage suppression on the single-phase power deviation is analyzed,and the feedforward control is proposed accordingly.Tests were carried out using a grid-connected MMC prototype system,and experimental results verified that the maximum common-mode voltage of the grid-connected system under severe asymmetric grid conditions can be reduced to 1/3N of its original value by the proposed control strategy,where N is the per-arm submodule number.Meanwhile,the unity power factor,constant DC voltage,and balanced single-phase power were also realized.
关键词
中压电机驱动系统/共模电压/并网模块化多电平变换器/电网故障
Key words
Medium-voltage motor driving system/common-mode voltage/grid-connected modular multilevel converter(MMC)/grid fault
维普
万方数据