Resonant Modular Multilevel DC-DC Converters for Both High and Low Step-Ratio Connections in MVDC Distribution Systems

Xin Xiang, Yunjie Gu, Yang Qiao, Xiaotian Zhang, Wuhua Li, Xiangning He, Timothy C. Green

Research output: Contribution to journalArticlepeer-review

18 Citations (SciVal)


DC transformers based on power electronics are key items of equipment for medium voltage dc (MVDC) distribution systems. Both high and low step-ratio dc-dc conversions are required to interface dc links at different voltages to form an integrated dc distribution system. The transformer-coupled resonant modular multilevel dc-dc converter (RMMC) is well-suited to high step-ratio connection between an MVDC network and a low voltage dc network but it is not suitable in low step-ratio conversion for linking two MVDC networks with similar but not identical voltages. This article presents a circuit evolution of the high step-ratio transformer-coupled RMMC into its low step-ratio transformer-less RMMC counterpart. These two RMMCs share the same structure and the same resonant process within the resonant submodule stack giving rise to the same operational advantages. Also, the circuit design experience can be readily transferred from one to the other. From these two base RMMC circuits, a family of RMMCs with further configurations is elaborated that provide a wider variety of connection options for MVDC distribution systems. In this circuit family, each high step-ratio transformer-coupled RMMC has a low step-ratio transformer-less RMMC counterpart and one can be transformed into the other via the circuit evolution process presented. The theoretical analysis for both high and low step-ratio RMMCs has been verified through full-scale simulations of medium voltage examples and further verified through down-scaled experiments on laboratory prototypes.

Original languageEnglish
Article number9296809
Pages (from-to)7625-7640
Number of pages16
JournalIEEE Transactions on Power Electronics
Issue number7
Early online date17 Dec 2020
Publication statusPublished - 1 Jul 2021


  • High step-ratio
  • low step-ratio
  • medium voltage dc (MVDC) distribution systems
  • resonant modular multilevel dc-dc converter (RMMC)

ASJC Scopus subject areas

  • Electrical and Electronic Engineering


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