基于模块化多电平换流器的多端口谐振型电力电子变压器

The medium voltage direct current (MVDC) port is essential to power electronic transformer (PET) applied to DC distribution network. The available PET topologies based on modular multilevel converter (MMC) can simultaneously provide four kinds of ports: medium voltage alternating current (MVAC), MVDC, low voltage direct current (LVDC) and low voltage alternating current (LVAC). However, the PET topologies need four power conversion stages, which lead to the complex circuit structure, large volume and heavier weight of PETs. A multi-port resonant PET topology based on MMC applied to DC distribution network is proposed. With a mixed-frequency modulation strategy, a set of LC resonant branches, medium-frequency transformers and full-bridge circuits are connected in parallel in the MMC bridge arm branch to realize the power decoupling outputs of the MVDC ports and LVDC ports. The proposed PET topology can provide the essential multi-port characteristics with only three power conversion stages, and has the advantages of the simplified circuit structure, smaller size and lighter weight. Moreover, the equivalent circuit analysis, control strategy and parameter design process of the proposed PET are presented. Finally, the simulation and experimental results show that the proposed PET topology is feasible.