模块化多电平变换器全电平产生原理及电容均压策略

Study on Full Level Generation and Capacitor Voltage Balance Strategy of the Modular Multilevel Converter

模块化多电平变换器每个桥臂有N个模块,根据调制方法的不同,输出可以产生N+1电平(基本电平)和2 N+1电平(全电平),文中研究了这两种输出的工作机理,以及对桥臂电感的影响,研究了电平产生、环流及电容电压控制之间的关系。在此基础上,针对载波重叠脉宽调制(PWM)策略,提出了一种基于PWM信号轮换的模块电容均压策略,该策略可以根据需要调整策略的执行时间,以减少因均压带来的开关状态变化。通过一个560V直流输入的实验和仿真平台验证了所提出均压策略的有效性。

There are N sub-modules in a multilevel converter,and according to different modulation rules,N +1 levels (basic levels) or 2N +1 levels (full levels) can be achieved.The working mechanism and effects on the arm inductor of the two output levels is proposed,and the relationship between level generation and circulating current and capacitor voltage control is studied.Based on which,for the carrier phase position pulse width modulation(PWM),a capacitor balance strategy based on PWM signals rotating is presented.With this strategy,the time of implementing the algorithm can be adjusted according to the need to reduce the change in the switching frequency caused by capacitor voltage balance.The conclusions and the strategy are verified with a 500 V dc input experimental platform.