一种模块化多电平DC/DC变换器的基频调制策略

A Fundamental Frequency Modulation for Module Multilevel DC/DC Converters

电气拓扑采用模块化多电平技术的高压大容量DC/DC变换器是构建直流电网的关键装备之一。与柔性直流输电系统中的工频运行工况不同,基于模块化多电平的DC/DC变换器可运行于中/高频。若仍采用工频工况下的最近电平逼近调制策略及电容排序均压,会带来子模块开关损耗大及数字控制系统运算负担重等一系列问题。为此,提出了一种适用于模块化多电平DC/DC变换器的基频调制策略,阐述了基频调制的基本需求及其实现方法,提出了与基频调制相应的电压及电压增量双排序均压策略,并分析了基频调制策略对子模块电容参数设计的影响。通过仿真和实验对提出的基频调制策略和双排序均压算法进行了验证,结果证明该调制策略能有效降低功率器件开关损耗,改善交流输出电压波形的总谐波失真,缓解数字控制系统的运算负担,并与控制策略具有良好的兼容性。

A fundamental frequency modulation strategy was proposed for the modular multilevel DC/DC（M2DC） converter aiming to reduce switching loss of sub-modules and calculation quantity of digital control system. The basic requirements and implementation method of the fundamental frequency modulation strategy were analyzed and a dualsorting capacitor voltage-balancing strategy that ensures power balance of each sub-module capacitor was proposed. The effect of the fundamental frequency modulation on the design of sub-module capacitor parameter as well as the compatibility of the control system were also analyzed. In order to verify the validity of the fundamental frequency modulation and dual-sorting capacitor voltage-balancing strategy, a simulation model in Matlab/Simulink and a low power prototype were built. The results show that this modulation strategy not only possesses a good compatibility with the control system, but also has a capability to reduce the power loss of switching devices and the stress of the digital control system.