Operational Reliability Model of Hybrid MMC Considering Multiple Time Scales and Multi-state Submodule

Environmental and electrical factors such as wind speed, air temperature and switching frequency have significant influences on the operational reliability of hybrid modular multilevel converter (MMC), which is commonly used for the wind power transmission. However, the existing reliability model of hybrid MMC based on statistics cannot accurately reflect the impact of these factors. In this paper, a new operational reliability model of hybrid MMC is presented. The reliability index of the hybrid MMC is coupled with its operation characteristics by calculating multi-term thermal cycling. In addition, an operation strategy of hybrid MMC is proposed to improve its reliability. The multi-state submodule (SM) is developed, which is capable of bypassing specific faulty power modules instead of the whole SM. Case studies show that the proposed operational reliability model could describe the impact of environmental and electrical factors. Also, the proposed operation strategy can improve the reliability of hybrid MMC by extending the operation time of SMs.