模块化多电平换流器的交直流侧阻抗模型

模块化多电平换流器(MMC)的阻抗建模是分析基于MMC的电力电子系统交、直流侧谐振及稳定性的基础条件。依据MMC的拓扑结构、运行及控制特性,同时考虑环流控制对MMC交、直流侧阻抗的影响,分别推导了MMC直流侧和交流侧的小信号阻抗解析模型。利用MATLAB/Simulink搭建了三相MMC详细时域仿真模型,采用注入小扰动电压/电流的方法测量MMC交、直流侧的小信号阻抗,与推导的MMC交、直流侧阻抗解析模型的计算结果比较,验证了解析模型的正确性。MMC阻抗模型仿真结果表明:在不加环流控制的情况下,MMC交流侧的小信号阻抗在低频范围内存在谐振峰;而加入环流控制后,该谐振峰能够得到有效抑制。

AC- and DC-side impedance models of modular multilevel converter

The impedance modeling of MMC(Modular Multilevel Converter) is the basis for analyzing the resonance and stability at AC and DC sides of MMC-based power-electronics system. While the impact of circulating current control on the AC-and DC-side impedances of MMC is considered, the DC-side and AC-side small-signal impedance analytical models of MMC are respectively derived according to its topological structure, operational features and control characteristics. A time-domain simulation model of three-phase MMC is built with MATLAB/Simulink and the AC-and DC-side small-signal impedances of MMC are calculated based on the derived analytical models, which are compared with the impedances measured by the method of small-disturbance voltage/current injection for verifying the accuracy of the analytical models. The simulative results show that, without circulating current control, the AC-side small-signal impedance has a resonance peak in low-frequency range; the resonance peak could be effectively restrained by the circulating current control.