Power Flow Control of Bidirectional Modular Multilevel Resonant Converters in MVDC and LVDC Distribution Networks

This article proposes a bidirectional modular multilevel resonant dc converter (BMMRDC) and its power flow control strategy for medium-voltage dc to low-voltage dc distribution network First, a brief description of the BMMRDC topology structure is provided, followed by a detailed investigation of its operational principles under different operating modes. Then, the voltage gain model is studied, and the relationship between the transferred power and the operating frequency is precisely built. On this basis, a bidirectional power control strategy is proposed to adjust power flexibly by regulating the switching frequency. Furthermore, the soft-switching behaviors of the medium-voltage side and low-voltage side devices are analyzed to guide the parameter design of the converter, enabling soft-switching operation under a wide range of operating conditions. Finally, a downscaled BMMRDC prototype is constructed to validate the feasibility of the BMMRDC topology and the proposed control strategy.