Modeling and Control of a Hybrid AC-DC-Modular Multilevel Three-port Converter

In order to realize the flexible interconnection between the HVDC transmission system, MVAC distribution system, and MVDC distribution system, a Modular Multilevel Three-port Converter (M2TC) is proposed in this paper. Based on the integrated 9-arm modular multilevel design, the power conversion series and power loss between medium voltage DC and medium voltage AC systems can be reduced. At the same time, by means of partial power conversion, the power rating and loss between medium voltage DC and high voltage DC can be reduced. In this paper, the current and power characteristics of the proposed topology are analyzed, and the corresponding converter modulation and control strategies are designed on this basis. Based on numerical simulation, the flexible adjustment capability of the proposed multi-port converter and the effectiveness of the voltage equalization control strategy are verified.