中文摘要：

模块化多电平换流器(MMC)桥臂中冗余子模块的存在是换流器可靠运行的重要保障,能够避免子模块故障时换流器无法正常运行甚至可能退出运行的风险。为此,分析了不同调制策略下冗余保护的换流器损耗,并基于此提出了基于载波移相调制的新型冗余保护策略。该策略在故障后根据子模块的运行状态进行载波动态分配,无需记录载波量;可通过改变载波来切换冗余子模块和未故障子模块的运行状态,优先为冗余子模块充电;同时,引入电容电压优化控制,以保证附加载波控制时桥臂的电容电压波动较小,降低相间环流和维持控制器的稳定。7电平和101电平MMC系统的仿真结果验证了所提冗余保护策略的有效性和通用性,且对系统控制稳定性影响较小。

英文摘要：

The existence of redundant sub-modules (SMs) is an important guarantee of reliability of modular multilevel converters (MMCs) to avoid the risk of abnormal operation and even outage.A novel redundant protection strategy based on carrier phase-shifted sinusoidal pulse width modulation(CPS-SPWM) is proposed,which includes carrier dynamic allocation, additional carrier control and optimization of capacitor voltage.The carrier dynamic allocation rearranges the carriers of SMs without additional records.The additional carrier control adjusts the state of the redundant SMs to retain their priority to be charged.The optimization of capacitor voltage is capable of maintaining slight fluctuation of the capacitor voltage as well as reducing the circulating current.Simulation results of a 7-level and a 101-level MMC system by PSCAD/EMTDC show that the proposed strategy is effective and generic for various voltage-level MMC systems to ensure successful converter operation when a SM fault occurs.