Implementation of Modular Multilevel Converter Exceeding 5 GW by Connecting Extra Full-Bridge Submodules

Modular multilevel converter (MMC) has become the mainstream converter in VSC-HVDC projects. However, the application of MMC still faces significant challenges in large-scale VSC-HVDC projects exceeding 5 GW. In order to solve the limitation of MMC capacity due to the current level of switching devices, the number of full-bridge submodules (FBSMs) utilized in MMC arm can be increased. The modulation index of MMC can be increased by utilizing negative-voltage states of the additional FBSMs. Thus, the AC component of the arm current can be decreased and the capacity of MMC can be increased. In the case study, the comparison of two capacity enhancement methods shows the economic advantages of the proposed method. The effectiveness of the proposed method is verified by simulation.