新型串联混合型模块化多电平变换器及其控制策略研究

Topology and Control Strategy of Novel Series Hybrid Modular Multilevel Converter

近年来,模块化多电平变换器(modularmultilevel converter,MMC)因具有模块化的结构特点,在柔性直流输电领域受到广泛关注。随着电压等级的提升,传统MMC拓扑的子模块数成倍增加,装置成本及体积大幅提高。为实现MMC的轻型化设计目标,提出一种串联混合型MMC(series hybridMMC,SHMMC)拓扑,对其工作原理进行介绍,并推导其数学模型。同时,针对相单元内部所存在的释能过电流问题展开讨论,设计适用于SHMMC拓扑的控制策略。MATLAB/Simulink仿真及样机实验研究结果表明该拓扑正确可行,且具有较好的输出特性及内部特性。在直流侧电压相同的情况下,所提SHMMC拓扑相较于传统MMC拓扑子模块数更少,在保障良好输出特性的前提下损耗更低,且无需设置桥臂电抗器,有利于降低装置体积,有效实现了轻型化设计目标。

In recent years,the modular multilevel converter(MMC)has drawn lots of interests in the voltage source converter-based high voltage direct current transmission applications due to its modular structure.The increasing the voltage level of the MMC requires more sub-modules and then leads to greater cost and bigger volumes.In order to realize the lightweight design of the MMC,a series hybrid modular multilevel converter(SHMMC)topology is proposed in this paper.The working principle is introduced and the mathematical model is deduced.Meantime,the energy release overcurrent problem in phase unit is discussed.In addition,to address the overcurrent problem,a control strategy suitable for the SHMMC topology is designed.The correctness and feasibility are verified by the Matlab/Simulink simulations and the prototype experiment.The great output and internal characteristics are also shown.Compared to the traditional MMC topology,the proposed SHMMC topology requires less sub-modules and removes the arm inductors under the same DC voltage,which helps reduce the device volume and realize the lightweight design.On the premise of ensuring good output characteristics,the SHMMC has a lower power loss.