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

适用于直流配电网的电力电子变压器(PET)需要中压直流端口,而现有基于模块化多电平换流器(MMC)结构的PET拓扑可同时提供中压交流、中压直流、低压直流和低压交流端口,但这类PET需要四级电能变换,使得电路结构复杂,体积和重量较大。文中提出了一种适用于直流配电网的多端口MMC谐振型PET拓扑。该拓扑采用混频调制策略,同时在MMC桥臂支路中并联一组LC谐振支路、中频变压器和全桥电路实现中压直流和低压直流端口的功率解耦输出。该PET拓扑仅使用三级电能变换即可提供所需的多端口特性,具有电路结构简单、体积重量较小等优势。针对该PET拓扑,提供了等效电路分析、控制策略和参数设计方法。最后,通过仿真和实验结果验证了该PET拓扑的可行性。

Multi-port Resonant Power Electronic Transformer Based on Modular Multilevel Converter

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.