中压电机驱动系统前端并网MMC共模电压抑制

Grid-connected MMC Common-mode Voltage Suppression at Front End of Medium-voltage Motor Driving System

为最大程度地保护基于模块化多电平变换器MMC(modular multilevel converter)无变压器背靠背中压电机驱动系统中的中压电机免受非对称电网故障和开关动作的影响,设计了前端无变压器配置并网MMC共模电压最小化控制策略。其中非对称电网故障引起的共模电压可由MMC生成对消电压消除,而MMC开关动作引起的开关纹波可由通过端到端布置桥臂电压脉冲来抑制;分析MMC共模电压抑制对单相功率偏差的影响,并据此提出了前馈控制;使用并网MMC样机系统开展测试。实验结果验证了在所提出控制策略作用下,并网系统在严重非对称电网条件下的最大共模电压可降至原来的1/3N(N为桥臂子模块数),同时还实现了单位功率因数、恒定直流电压和平衡单相功率。

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.