Operational Analysis and Control of a Multi-Port Solid-State Transformer

The modular multilevel multi-port solid-state transformer is an attractive topology for simultaneously interconnecting and managing bidirectional power transfer among the MVAC grid, the MVDC grid, and the LVDC bus, thus providing a high degree of operational flexibility. Identical isolated DC-DC converter stages incorporating medium-frequency transformers are integrated into the submodules to achieve the required voltage conversion and galvanic isolation between the medium-voltage and low-voltage sides. This paper outlines the fundamental operating principles and system-level control strategies using an analytical average model. A novel energy balancing method exploiting the isolated DC-DC converters is proposed. Finally, the converter's operating behaviour, along with the proposed control strategies and energy-balancing methods, are verified using time-domain simulations of the switched model for a 2 MVA system.