中文摘要：

模块化多电平换流器（modular multilevel converter,MMC）子模块电容均压问题,是MMC型高压直流输电系统稳定运行的关键。当桥臂子模块数过多时,采用传统的排序均压算法将使电容电压排序运算量过大,这对控制器的硬件设计带来巨大挑战。针对传统均压算法的问题,提出了一种改进的电容电压平衡方法,通过对子模块分组,减少了电容电压排序运算量,同时采用一种组间电压平衡算法,解决了各组间电压不平衡问题。在此基础上,类比整数质因子分解思想进一步优化,得到电容电压平衡分组排序的最优化方法。在实时数字仿真器RT-Lab中搭建了模块化多电平换流器直流输电系统（modular multilevel converter high voltage direct current,MMC-HVDC）模型进行仿真验证,仿真结果表明,改进方法及最优化方法能在维持子模块电容电压平衡的同时,大大提高仿真计算速度,从而验证了所提出方法的有效性和可行性。

英文摘要：

The capacitor voltage balancing of modular multilevel converter（MMC） determines the stable operation of MMC based high voltage direct current（HVDC） transmission system. When the number of sub-modules（SMs） is excessive, it requires a large amount of computation time, which poses a challenge to the design of the physical controller. To solve this problem, this paper proposed an improved capacitor voltage balancing method. The improved method grouped the SMs to reduce the computing quantity of sorting the capacitor voltages, and maintained the voltage balancing between groups by adopting the voltage balancing algorithm between groups. Then the optimization method inspired by the prime factorization principle is put forward. A MMC-HVDC model was developed in RT-Lab. The simulation results show that the improved method and the optimization method can both reduce the amount of computation and improve the simulation speed significantly with the balancing of capacitor voltages. All those results verify the effectiveness and feasibility of the improved method and the optimization method.