Abstract: There are many advantages for modular multilevel converter (MMC), such as modular structure, scalability and reduced harmonics, which makes it become a potential converter technology for high voltage direct current (HVDC) transmission system. The basic topology structure and working principle are introduced, capacitor voltage fluctuation and circulation current are analyzed, and point out the necessity of controlling. Capacitor voltage balancing control based on circulation current suppression strategy are applied to keep voltage stability of sub-module(SM) capacitor and suppress circulation current. Circulation current suppression controller based on low pass filter and quasi-proportional resonant controller is designed and added to additional capacitor voltage balancing control strategy. The effectiveness and feasibility of the proposed method is proved by Matlab/Simulink, the simulation results show that the fluctuation of capacitor voltages as well as the circulating current can be confined into acceptable range.

Key words: Modular multilevel converter, high voltage direct current transmission, capacitor voltage balancing, circulation current suppression

摘要： 模块化多电平换流器(MMC)的模块化结构、可扩展性、谐波含量少等特点使其在高压直流(HVDC)输电领域具有很好的发展潜力。分析了MMC的基本拓扑结构和工作原理，同时对电容电压波动和环流进行分析，指出对两者进行控制的必要性。提出一种基于环流抑制策略的电容电压平衡控制，在电容电压附加平衡控制的基础上设计基于滤波器、准比例谐振控制的环流抑制器，使得各子模块电容电压稳定的同时也抑制了环流，最后通过Matlab/Simulink验证了该控制方法的有效性和可行性，仿真结果表明电容电压波动和环流被控制在合理范围内。

关键词: 模块化多电平换流器, 高压直流输电, 电容电压平衡, 环流抑制