隔离型模块化多电平直流变换器子模块电容电压综合控制策略

A Comprehensive Sub-module Capacitor Voltage Control Strategy of Isolated Modular Multilevel DC Converter

针对桥臂参数不对称及轻载工况导致隔离型模块化多电平直流换流器(isolated modular multilevel DC converter,IMMDC)子模块电容电压发散问题,文中提出一种IMMDC桥臂子模块电容电压综合控制策略,包括两个层面,分别是上下桥臂电容电压平衡控制和桥臂内子模块电容电压平衡控制:针对桥臂参数不对称问题,建立表征IMMDC内部动态特性的通用数学模型,揭示在双向功率传输下桥臂参数不对称导致上、下桥臂电容电压不平衡及桥臂交流环流产生的机理。在此基础上,提出基于脉宽调制(pulse width modulation,PWM)+移相的IMMDC上下桥臂电容电压平衡控制方法,实现IMMDC上、下桥臂电容电压平衡,并有效抑制交流环流;针对IMMDC的不同工作模式、不同变换器电压匹配比导致常规排序法失效的问题,提出一种基于单排序的工作模式自适应的桥臂内子模块电容电压平衡控制方法,实现全运行工况下IMMDC桥臂内子模块电容电压的平衡控制。最后,通过仿真和样机实验验证所提控制策略的有效性。

In order to balance the sub-module capacitor voltages of isolated modular multilevel DC converter(IMMDC)under asymmetric parameters and light load conditions,this paper proposed a comprehensive sub-module capacitor voltage control strategy for IMMDC,including two layers,i.e.,arm-balancing control and inner-arm balancing control.A general mathematical model of IMMDC was established considering the arm parameters asymmetry,which reveals the mechanism that the asymmetry of the arm parameters leads to the imbalance of the capacitor voltages and the generation of the ac circulating currents under bidirectional power transmission.Subsequently,an arm-balancing control method based on pulse width modulation(PWM)combined with phase-shift control was proposed to balance the sub-module capacitor voltages and to suppress the ac circulating currents.Besides,considering that the conventional inner-arm balancing control method may be invalid under different operation modes and voltage gains,an operation-mode adaptation inner-arm sub-module capacitor voltage balancing control method was also proposed to balance the inner-arm sub-module capacitor voltages.Finally,the effectiveness and feasibility of the proposed comprehensive sub-module capacitor voltage control strategy were validated by the simulation and experiment.