一种改进的MMC电容电压平衡控制策略

Research on An Improved MMC Capacitor Voltage Balance Control Strategy

针对模块化多电平变换器中子模块电容电压的平衡问题,提出循环置换映射电容电压平衡策略.通过改进的载波移相调制方式对子模块进行初步选择,选择的信号经过循环置换映射电压平衡单元筛选.该平衡单元在置换时间内将开关门信号均匀地分配到各桥臂的子模块之间,得到占空比相同的导通信号,利用桥臂的平衡控制输出稳定的电压波形.在PSACD/EMTDC软件中搭建仿真系统,仿真结果表明:电压波动在一定范围内,电压纹波基本一致,在较宽频率范围内实现电压平衡控制.所提出的策略能减少对子模块电容电压的监测,减少计算量,降低对系统参数的依赖,有效抑制电压纹波影响.

In order to cope with the balance problem of capacitor voltages of sub-modules in modular multilevel converters,a new method of circulate permutation mapping was proposed.Through the improved carrier phase shift modulation mode,the sub-modules were preliminarily selected.Signals were screened by cyclic displacement mapping voltage balance units,which distributed the opening and closing signals evenly among the submodules of each arm during the replacement time,obtained gate signals with the same duty cycle,and sent out stable voltage waveforms through balance control of the bridge arm.By building simulation system in PSCAD/EMTDC,the simulation results show that the voltage fluctuation stays within a range,the voltage ripples are basically consistent,and voltage balance control is realized in a wide frequency range.The proposed method in this paper helps to reduce the monitoring of capacitor voltage of sub-modules,to reduce the calculation amount,to reduce the dependence on system parameters,and to effectively suppress the effect of voltage ripples.