Conditional Probability-Based Reliability Evaluation of MMCs Considering Dependency of Submodules

The modular multilevel converter (MMC) has been widely used in the high-voltage direct current transmission system. To ensure the safe and reliable operation of the transmission system, it is necessary to conduct the reliability evaluation of the MMC. In the previous studies, the dependent relationship among submodules (SMs) tends to be neglected, which may result in the error of the reliability modeling for the MMC. To fill this gap, combined with the conditional probability method, the reliability model of the MMC is constructed considering the dependency of SMs. First, the effect of current levels flowing through SMs on the reliability of SMs is analyzed based on the conditional probability method. Then, the reliability model of the MMC considering dependency with the hierarchical structure is established in turn. On the basis, the reliability evaluation of the MMC considering the dependent relationships among the SMs can be developed successfully, which depicts the reliability of the MMC more accurately. The effectiveness of the proposed method is validated in case studies.