Research on the modular multilevel converter applied to multi-terminal DC transmission system

The multi-terminal DC transmission (MTDC) is one of the development trends of the future grid, and the modular multilevel converter (MMC) had been confirmed that it suits for the multi-terminal DC transmission system. On the basis of predecessors' study, this paper introduces the structure of MMC, and the equations of MMC are summed up. Then, the basic modulation technologies of MMC are introduced separately. Finally, some improved modulation technologies of MMC are introduced.