Operational Reliability Assessment of Power Electronic Transformer Considering Operating Conditions and Fatigue Accumulation

Power electronic transformer (PET) is a new type of Distribution FACTS. The equipment reliability is directly determined by its historical operating conditions and the component health status, especially the IGBT modules. This paper proposes an operational reliability model for the power electronic transformers based on MMC, which considers the effects of the fatigue accumulation and short-term operating conditions of IGBT modules. Firstly, the loss of IGBT modules under different loads is analyzed to obtain their long-term and short-term junction temperature. Then, the contributions of different time-scale junction temperature variations on the IGBT module failure rate are analyzed based on IGBT failure mechanisms and reliability guidelines. Finally, the Markov state space for the PET reliability is established, and the validity of the operational reliability model is verified by a case study. The results show that the proposed method could effectively predict the time-varying equipment reliability performance in the short-term operation.