模块化多电平换流器的桥臂聚合模型

模块化多电平换流器（MMC）在新能源并网、岛屿供电等方面具有独特的优势，得到了越来越广泛的应用.由于MMC子模块数众多，导致其电磁暂态仿真计算量大、耗时多，增加了MMC设计和优化的难度，更不利于含MMC电力系统的电磁稳定性仿真分析，因此需要建立准确高效的仿真模型以便于对系统不同的运行方式和工况进行分析.依据MMC子模块工作模态，分析了MMC桥臂的工作模式，建立了一种可适用于系统级分析的桥臂聚合模型，推导了其参数的计算方法.最后在PSCAD/EMTDC中搭建了一个49电平MMC详细电磁暂态模型及其等效聚合模型，对比了两种模型在VSC-HVDC的启动、运行、故障时的动态过程.结果表明，所提出的MMC聚合模型可以精确模拟各种工况下MMC的系统级行为. 

Equivalent Modeling of MMC-HVDC Transmission System

Modular multilevel converter (MMC) has outstanding advantages in the application of new energy transmission, island power supply, and etc, adopted in more and more applications. Due to the large number of sub-modules in MMC, the electromagnetic transient simulation is difficult and time-consuming, which increases the difficulty of design and optimization of MMC and the stability analysis of power system with MMC. Therefore, an accurate and efficient simulation model should be established to analyze the system in different operation conditions. In this paper, based on the operation-mode of the MMC sub-module, a working mode of the MMC bridge arm was analyzed. And then, an equivalent aggregated model was derived for system-level analysis. Finally, a 49-level MMC detailed electromagnetic transient model and its equivalent aggregation model were built in PSCAD/EMTDC. The dynamic processes of the two models in the startup, operation and fault of VSC-HVDC were compared. The results show that the proposed MMC aggregation model can accurately simulate system-level behavior of MMC under various working conditions.