Reliability modeling and evaluation of MMCs under different redundancy schemes

Jingli Guo, Xiuli Wang, Jun Liang*, Hui Pang, Jorge Goncalves

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Due to the demand for high reliability, modular multilevel converters (MMCs) are designed with redundant submodules. Redundant submodules can be integrated into the converter by employing different redundancy schemes: The conventional active scheme, the load-sharing active scheme, and the passive scheme. Different schemes have different impacts on the improvement of converter reliability. The contributions of this paper include that an analytical method is proposed to evaluate the reliability of MMCs under different redundancy schemes and the factors' influence on the converter reliability is analyzed to determine the proper redundancy scheme. Reliability models of MMCs under different redundancy schemes are built using Markov chains and the iteration method. Based on the proposed models, the effects of redundant schemes are evaluated in terms of the converter reliability. A case study is conducted to validate the feasibility and robustness of proposed models and to specify the conditions in the favor of each redundancy scheme. The benefits of sharing redundancy among arms are also explored from the reliability point of view. If insulated-gate bipolar transistors (IGBTs) and capacitors are dominant components in a submodule in terms of failure rates, the load-sharing active scheme performs better; otherwise, setting the redundant submodules in an idle state is more effective. It is also found that the number of required redundant submodules is greatly reduced by sharing redundancy among arms.

Original languageEnglish
Article number7962248
Pages (from-to)2087-2096
Number of pages10
JournalIEEE Transactions on Power Delivery
Issue number5
Early online date29 Jun 2017
Publication statusPublished - 1 Oct 2018

Bibliographical note

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  • Load-sharing redundancy
  • modular multilevel converter
  • passive redundancy
  • redundancy scheme
  • reliability assessment


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