The utility model discloses a MMC topological structure, a serial communication port, including the three bridge arm of three -phase, wherein, three bridge arm contains a N+1 module, a N+1 reactance and a N module electric capacity respectively, the submodule piece comprises two thyristor inverse parallels, the one end of submodule piece is established ties with a reactance respectively, and the other end all links on the bridge arm at submodule piece place, submodule piece electric capacity is established ties respectively between two adjacent reactance. The utility model discloses a MMC topological structure can effectively solve the availability of prior art equipment, problem that the equipment running cost is high.