动态均压偏差率下的MMC均压控制策略

Voltage-sharing control strategy of MMC under DVDR

现有模块化多电平换流器(MMC)的调制策略主要基于比较型排序方式,存在算法复杂、计算负荷大、子模块(SM)频繁投切、系统损耗较大等缺陷。针对上述问题,文中提出一种基于动态均压偏差率(DVDR)的系统调制方式。首先,将子模块电容电压与其平均值作差得到差值序列,将差值序列按正负进行快速分组;然后,针对所得子序列设置动态均压偏差率,计算得到必要动作子模块(NASM),只需对于单一子序列中必要动作子模块序列进行排序即可降低系统计算负荷;其次,结合优化开关频率控制设置不同电压阈值与降频因子,通过判断桥臂电流方向,在保持电压一致性的前提下降低功率器件开关频率,减少电压波形畸变率;最后,在Matlab/Simulink平台上搭建仿真实验模型,验证文中所述控制策略的可行性。

The modulation strategy of the existing modular multilevel converter(MMC)is mainly based on the comparative sort mode,which has the disadvantages such as complex algorithm,high computational load,frequent switching of sub module(SM)and high system loss. On this basis,a new system modulation mode based on DVDR(dynamic voltage deviation rate)is proposed. The difference sequence is obtained by the deduction between the capacitor voltage of the SM and its average value,and the difference sequence is quickly divided into positive and negative sub sequences. Then the dynamic voltage-sharing deviation rate is set for the obtained sub sequences,the necessary action sub module(NASM)is calculated,and the NASM sequence in the single sub sequence is sorted merely to reduce the calculation load of the system. The different voltage thresholds and frequency reduction factors are set by combining with optimized switching frequency control. By judging the current direction of the bridge arm,the switching frequency of power devices is reduced and the voltage waveform distortion rate is reduced under the premise of maintaining voltage consistency. The simulation experiment model is built on the Matlab/Simulink platform to verify the feasibility of the control strategy.