Reliability modeling and analysis of hybrid MMCs under different redundancy schemes

Xiangjie Xie, Hui Li, Alasdair McDonald, Hongtao Tan, You Wu, Tian Yang, Wei Yang

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


The hybrid modular multilevel converter (HMMC), consisting of half-bridge and full-bridge submodules (SMs), has become a competitive topology due to the DC fault ride-through capability (FRTC). Redundancy schemes need to be employed to improve the reliability, including fixed-level and voltage-sharing active schemes, as well as passive scheme. However, different schemes affect reliability differently, which entails specific models. The contributions of this paper involve that analytical reliability models of HMMCs are proposed with considerations of voltage stress in active scheme, as well as imperfect bypass switch in passive scheme, and the comparison of different schemes is conducted to help the redundancy design. The reliability of HMMCs is divided into basic and extra components by the requirement of FRTC, which are modeled through the Markov chain and iteration method. A case study is conducted to validate the feasibility and accuracy of the proposed models, and the reliability analysis is presented, together with comparisons of different redundancy schemes. The results illustrate that reliability improvements of both fixed-level mode and passive scheme are prone to suffer saturation effect with the increase of redundant half-bridge SMs, which may even cause reliability decline in voltage-sharing mode.
Original languageEnglish
Pages (from-to)1390-1400
Number of pages11
JournalIEEE Transactions on Power Delivery
Issue number3
Publication statusPublished - 9 Jul 2021


  • hidden Markov models
  • redundancy
  • power system reliability
  • stress
  • analytical models
  • switches
  • hybrid submodule
  • modular multilevel converter (MMC)
  • redundancy scheme
  • reliability modeling
  • design


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