Design and parameter configuration of modular multilevel dynamic DC transformer for renewable energy sources

DC transformer plays a significant role in DC distributed network. This study proposes a modular multilevel dynamic DC transformer (MMDT), which can realise smooth control of transformer ratio, multi-level voltage conversion, and reliable fault isolation without high-frequency transformers and extra loss. The inner circuit, formed by the capacitors, not only realises the energy exchange between different sides but also provides the capability of fault isolation. In the proposed MMDT, the voltage transforming is realised by switching to different numbers of control units (CUs) on each side. To realise multi-level voltage transforming, the multi-port MMDT is developed. Furthermore, this study offers analyses of the current and voltage characteristics in steady-state and investigates the parameter design method in detail. Finally, the simulation and experiment tests are conducted to verify the feasibility and superiority of the proposed MMDT.