Abstract：The traditional reliability analysis methods of the modular multilevel converter (MMC) either focused on half-bridge MMC only or ignored the sub-module (SM) correlations. As one of the potential candidates in future HVDC systems, this paper proposes the decoupled SM correlations-based reliability modelling approach for the half- and full-bridge hybrid MMC. Firstly the reliability model for the individual SM is established. Secondly a Copula function-based coordinate transformation is employed. According to the principle that the reliability of the series system among all the SMs is constant before and after coordinate transformation, the formulas of the coordinate transformations for half- and full-bridge MMCs are proposed respectively and further the corresponding formulas for hybrid MMC are deduced. After the transformation, the correlations among the SMs are decoupled so that the classical probability models can be applied. Finally, the calculations in Matlab have verified the feasibility of the proposed approaches. Finally, the calculations in Matlab have verified the feasibility of the proposed approaches.
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2019, Vol. 34 
