Reliability Analysis of MMCs Considering Submodule Designs with Individual or Series-Operated IGBTs

Jingli Guo, Jun Liang, Xiaotian Zhang, Paul D. Judge, Xiuli Wang, Tim C. Green

Research output: Contribution to journalArticlepeer-review


The half-bridge-based modular multilevel converter (MMC) has emerged as the favored converter topology for voltage-source HVDC applications. The submodules within the converter can be constructed with either individual insulated-gate bipolar transistor (IGBT) modules or with series-connected IGBTs, which allows for different redundancy strategies to be employed. The main contribution of this paper is that an analytical method was proposed to analyze the reliability of MMCs with the consideration of submodule arrangements and redundancy strategies. Based on the analytical method, the relative merits of two approaches to adding redundancy, and variants created by varying the submodule voltage, are assessed in terms of overall converter reliability. Case studies were conducted to compare the reliability characteristics of converters constructed using the two submodule topologies. It is found that reliability of the MMC with series-connected IGBTs is higher for the first few years but then decreases rapidly. By assigning a reduced nominal voltage to the series valve submodule upon IGBT module failure, the need to install redundant submodules is greatly reduced.

Original languageEnglish
Pages (from-to)666-677
Number of pages12
JournalIEEE Transactions on Power Delivery
Issue number2
Early online date26 May 2016
Publication statusPublished - 1 Apr 2017

Bibliographical note

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  • Modular multilevel converter (MMC)
  • reduced nominal voltage operation
  • redundancy analysis
  • reliability assessment
  • voltage capability


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