MMC交流侧非全相运行时电气量特性分析

Analysis of AC-side Electrical Characteristics of MMC in Open-phase Operation

确定非全相运行对模块化多电平换流器运行特性的影响,不仅是保证模块化多电平换流器安全运行的前提,也是设计新的控制和保护方法的基础。本文首先根据非全相运行时的边界条件得到了模块化多电平换流器交流侧等效序网图;然后,基于得到的序网关系,对工作于不同工作状态的模块化多电平换流器交流侧和直流侧电压、电流的变化情况进行了研究,研究表明,非全相运行不仅将导致模块化多电平换流器换流器交流侧出现过电压、过电流,还将使得直流侧电压、电流出现二倍频波动;最后,在PSCAD软件中搭建了双端柔直系统模型进行了仿真验证。

Determining the influences of open-phase operation on the operating characteristics of a modular multilevel converter is not only the premise of ensuring the safe operation,but also the basis for designing new control and protection methods.First,the equivalent sequence network diagram of the modular multilevel converter is obtained according to the boundary conditions of open-phase operation.Then,based on the obtained relationship of sequence network,the voltage and current characteristics on the grid-and DC-side of the modular multilevel converter under different working conditions are studied.Results show that the open-phase operation will not only cause over-voltage and over-current on the AC-side of the converter,but also will cause double-frequency fluctuation to the DC-side voltage and current.Finally,a two-terminal system model is built in PSCAD,and the theoretical analysis is verified through simulations.