基于降低开关频率的MMC优化排序算法

Optimized sorting algorithm of capacitor voltage for MMC based on reduced switching-frequency modulation

模块化多电平变换器(Modular Multilevel Converter,MMC)由于其具有较高的输出电平数、耐压等级高、波形质量好等众多优点而被广泛研究,并已运用于柔性直流输电工程中。子模块电容电压的均衡问题一直以来都是MMC众多研究热点之一。传统电容电压排序法会实时的对电容电压大小进行升降序排列,并在下一时刻按照桥臂电流的方向选择合适的子模块投入。但随着MMC子模块数目的增多,系统中开关器件的开关频率及损耗会随之增加。文中提出了一种新型的优化排序算法,设置相应电压的阈值,考虑上一时刻子模块的投切状态基础上进行电压排序,减少子模块开关动作次数,从而达到减小损耗的目的。在Matlab/Simulink中搭建MMC模型进行仿真验证,仿真结果验证了所提算法的有效性。

The modular multilevel converter(MMC)has a widely research due to its advantages of high output level,stricter withstanding voltage and good waveform quality,and has been applied in flexible direct current transmission engineering.The balance of sub-modular capacitor voltage has always been one of the research focuses in the field of MMC.The traditional capacitor sorting voltage algorithm will perform the up-and-down arrangement of the capacitor voltage in real time and select appropriate sub-modules according to the direction of the leg current in the next time.However,the increasing number of MMC sub-modules will cause higher switching frequency and larger switching losses.This paper puts forward a novel optimized sorting algorithm for capacitor voltage balancing.This strategy,considering the switching state of sub-module at the last moment,sets the related threshold voltage to reduce switching operation times and the losses.Finally,this paper builds the MMC module in Matlab/Simulink platform for simulation and verification.The simulation results show the effectiveness of the prospered algorithm.