Reliability model of MMC-based flexible interconnection switch considering the effect of loading state uncertainty
Flexible interconnection switch (FIS) is a power electronic device applied to electrical distribution system to realise the flexible control of power flow. Due to the fact that the reliability of FIS tends to be influenced by its operating conditions and dynamic characteristics during its actual operation, it is of significance to characterise the effects of loadings on reliability of FIS. Therefore, an improved reliability model of FIS is proposed, considering the state uncertainty of current and voltage loadings. First, the structural reliability model of modular multilevel converter (MMC) is established. Next, in view of the uncertainty of source and load in distribution network, Monte Carlo simulation is used to deal with the random current loadings, thus the equivalent reliability model of insulated gate bipolar transistor module is built. Then, considering the arm's voltage loading sharing mechanism, a state-dependent arm reliability model is built. Finally, an eight-state reliability model for the entire FIS is developed, and Markov-based analytical method is used to solve it. With the standard test system as well as the actual project in Hangzhou are taken as the testing systems, the reliability indices of FIS are calculated and compared with the field data. The numerical results validate the validity of the proposed model.