Isolated Multi-port DC-DC Converter-Based on Bifurcate MMC Structure

High voltage DC-DC converters are required to connect DC grids with different voltage levels in high-voltage direct current (HVDC) transmission systems. In this paper, a multi-port DC-DC converter based on bifurcate MMC is proposed. The proposed topology has three isolated DC ports and is characterized of its bifurcate arms. Conventional isolated DC-DC MMC have been widely used in HVDC applications and are able to connect a low-voltage DC source to a high-voltage DC source. However, when connecting three or more different DC terminals, the traditional solution is to use a multi-winding transformer or multiple MMCs. In the proposed converter, multiple output ports are generated by arm bifurcating so that multiple dc terminals can be connected. Compared to the scenario with two isolated conventional MMCs, the proposed converter consumes fewer submodules. Analysis and the control scheme for the proposed converter are also presented in detail. The effectiveness and performance are also evaluated by simulation results in MATLAB/Simulink.