MMC直流电压控制策略研究

Study on DC Voltage Control Strategy in MMC

为了对模块化多电平换流器(MMC)的直流侧电压进行控制并减小开关损耗,首先介绍了MMC的结构及子模块充放电原理,然后提出了MMC的直流电压控制是由系统级直流电压控制和子模块电压控制两部分构成;针对系统级直流电压控制,分析了直流电压控制原理,并提出相应的控制策略;针对子模块控制中存在的因开关器件盲目动作而产生的开关频率高的现象,提出了一种改进型子模块电压均衡控制策略,通过对传统电压排序方法的改进,避免了这一现象。最后以PSCAD/EMTDC为平台进行仿真研究,结果表明MMC直流侧电压可以稳定在额定值,并且器件开关频率明显降低。

In order to control the DC voltage in modular multilevel converter（MMC） and reduce the switching loss,the structure of MMC and the principle of sub-module charging are introduced firstly,and it is pointed out that the DC voltage control in MMC includes two parts,the DC voltage control of system and sub-module.For the DC voltage control in system,its control theory is analyzed,and the corresponding control strategy is proposed.At the same time,for the high switching frequency caused by the blind action of switching devices in the sub-module control,an improved voltage balance control strategy for sub-module is proposed by the improvements of the traditional voltage sorting method.In the end,PSCAD/EMTDC simulation results show that DC voltage in MMC can run in the rated value steadily,and the switching frequency is reduced significantly.