模块化多电平变流器预充电优化策略研究

Precharge Optimization Strategy of Modular Multilevel Converter

模块化多电平变流器(MMC)正常运行前需将子模块电容电压预充电至额定值,所提预充电过程分为不可控预充电和可控预充电两个阶段。不可控预充电利用限流电阻和旁路开关有效降低充电电流幅值,通过分析等效充电回路,推导出限流电阻表达式。可控预充电阶段充分利用限流电阻的限流能力,通过控制策略进一步提升子模块电容电压至额定值。所提预充电控制策略结构简单、易实现,针对上、下桥臂充电不均衡和充电时间较长的问题给出了优化方法。最后,搭建三相MMC实验平台,实验结果验证了所提控制策略的有效性。

The submodule capacitor voltage of modular multilevel converter（MMC） need to precharge to the rated value before normal operation.The precharging process mentioned is divided into two stages ： uncontrollable precharge and controllable precharge.In the uncontrollable precharging, the current limiting resistor and the bypass switch are used to reduce the amplitude of the charging current.Through the analysis of the equivalent charge circuit,the expression of the current limiting resistor is deduced.The controllable charging process takes advantage of the current limiting resistor and further enhances the sub-module capacitor voltage to the rated value by the control strategy.The proposed precharge control strategy is simple and easy to implement, and the optimization method is given for the problem of unbalanced charging and long charging time.Finally, the three-phase MMC experimental platform is set up.The experimental results verify the effectiveness of the proposed control strategy.