Reliability Improvement to UPFC With Routine Test to the Abnormal State

The unified power flow controller (UPFC) helps to control the power flow, but its outage due to the abnormal state is a threat to power systems. In this paper, based on the proportion of the random failure, the transition rates of the abnormal state are newly derived. The impact of the routine test (RT) on the transition rates is quantified. The state space models of the UPFC based on voltage-source converter (VSC) and modular multilevel converter (MMC) are extended with the states introduced by the RT. The frequency and duration method is used to aggregate the states. The sensitivities of the availability and outage frequency of the UPFC with respect to the failure rates of the components are newly derived to find the vulnerable component and the optimal RT interval. The numerical results show that the RT reduces the probability of the abnormal state, reduces the failure duration, and improves the availability of the UPFC.