Reliability assessment of bidirectional power converters in battery energy storage systems of the DC microgrid

The bidirectional power-converter (BPC) reliability of battery energy storage systems (BATT-ESSs) in a local off-grid energy community (LOEC) is susceptible to dynamic and fault scenarios. As a great advantage of the BPC, it is widely used for balancing the power between all generating sources and all required loads in the DC microgrid (MG). However, a possible reduction in the BPC reliability of the BATT-ESS is inevitable due to different charging/discharging levels of this BATT-ESS in the DC MG. To make this assumption clear, the novel reliability analysis of the BPCs in BATT-ESSs is proposed in this paper by taking into account their dynamic and transient scenarios in the DC microgrid. The dynamic-voltage-based failure rate (DVBFR) and the fault-current-based failure rate (FCBFR) respectively from dynamic and fault scenarios of the BPC are two main objectives of the reliability study. These two failure rates are combined with the useful-time-based failure rate (UTBFR) and a Markov-based reliability model to give more holistic reliability evaluation results. Experimental results show that the FCBFR of the BPC in the BATT-ESS is larger than its DVBFR. The reliability of the BPC at the system level could be considerably decreased by multiple repeated dynamic cases. For component-level reliability of the BPC, the DVBFR of diodes is also the least impacted by the dynamic cases. Exponential and logarithmic functions are used to describe approximately the rapidly-increasing trendlines of FCBFRs of power-electronic elements in the BPC under the faulted operation cases. Moreover, reliability indices such as mean-time-to-failure (MTTF), mean-time-between-failures (MT BF), and the reliability index (R) of the BPCs in the BATT-ESSs are also quickly decreased by their fault and dynamic cases. (c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).