中文说明：
MATLAB仿真程序，基于直流输电系统（HVDC）的MMC（modular multilevel converter）结构变流系统。程序主要包括主变流部分及其控制部分，MMC为7电平结构。程序测试OK。
English Description：
Matlab simulation program is based on MMC (modular multilevel converter) structure converter system of HVDC system. The program mainly includes the main converter part and its control part, MMC is 7-level structure. Program test OK.