## 7 Conclusions  
Despite significant efforts to design several DC-DC converter topologies appropriate for fuel cell applications, there is a paucity of thorough research on the reliability and thermal performance of these converters. This paper presented an in-depth thermal and reliability analysis of five commonly used DC-DC boost converters in fuel cell systems. The thermal analysis was performed based on determining semiconductor devices' junction temperature via a thermal network model. Then, a power cycling test was done by applying a periodic power (with a frequency of 1 Hz) on the semiconductors so as to calculate the number of cycles to failure as the most critical indicator in reliability assessment. The results showed that the conventional boost converter (with a maximum IGBT junction temperature of \(\sim\)110 \({}^{\circ}\)C) has the weakest thermal performance among the studied converters. The switching devices in the Cuk converter were also likewise subjected to significant thermal stress. In contrast, the floating interleaved boost converter was able to get the first rank in terms of thermal performance, and a temperature of \(\sim\)62 \({}^{\circ}\)C was recorded for the IGBTs used in this converter. In terms of reliability, the conventional boost converter remains the least reliable (with \(N_{f}\sim\) 174k cycles), while the floating interleaved boost converter is likewise the most reliable choice. The interleaved boost converter has also demonstrated remarkable lifespan performance, ranking second (\(N_{f}\sim\) 6300k cycles). The analysis, including both thermal/reliability aspects, revealed that the floating interleaved boost converter performs much better compared to the conventional boost and other considered topologies. To observe the effect of other indicators (i.e., the number of circuit components and cost), a ranking methodology named TOPSIS has been used to arrange the converters according to their overall performance score. In the first scenario, the weights taken into account for the reliability indicator, maximum IGBTs' temperature, maximum diodes' temperature, number of total components in the circuit, and cost which were 0.2, 0.2, 0.2, 0.1, and 0.3, respectively. The cost weight was assumed to be predominant in this scenario. The findings of this scenario revealed that the floating interleaved boost converter rated best in terms of overall performance, whereas the Cuk converter ranked worst when several indications were considered. Additionally, a second scenario was considered in which, unlike the first scenario, the reliability indicator (0.3) was more important than the cost (0.2). By considering a greater weight (0.3) for the cost criterion than the reliability (0.2), the conventional boost converter ranked fourth among the examined converters. In addition, the results showed that the floating interleaved boost converter would be the most proper choice for fuel cell applications as it is always at the top of the list in different scenarios (performance scores of 0.67 and 0.74 for the two chosen scenarios, respectively), while the poorest results have been found in the Cuk converter in both scenarios. Evaluation of other proposed topologies (e.g., Z-source converter) for fuel cells in terms of reliability and thermal performance should be considered as a future study. Conceptualization, O.A. and M.D. ; methodology, O.A. ; software, O.A. and M.D. ; validation, O.A. ; formal analysis, O.A., T.R., W.D.C. and M.D. ; investigation, O.A. and M.D. ; resources, T.R., W.D.C. and M.D. ; data curation, M.D. ; writing--original draft preparation, O.A. ; writing--review and editing, T.R., W.D.C. and M.D. ; visualization, O.A. ; supervision, W.D.C. and M.D. ; project administration, M.D. ; funding acquisition, M.D. All authors have read and agreed to the published version of the manuscript.