System-level Reliability Assessment of Power Stage in Fuel Cell Application

High efficient and less pollutant fuel cell stacks are emerging and strong candidates of the power solution used for mobile base stations. In the application of the backup power, the availability and reliability hold the highest priority. This paper considers the reliability metrics from the component-level to the system-level for the power stage used in a fuel cell application. It starts with an estimation of the annual accumulated damage for the key power electronic components according to the real mission profile of the fuel cell system. Then, considering the parameter variations in both the lifetime model and the stress levels, the Weibull distribution of the power semiconductors lifetime can be obtained by using Monte Carlo analysis. Afterwards, the reliability block diagram can further be adopted to evaluate the reliability of the power stage based on the estimated power semiconductor reliability. In a case study of a 5 kW fuel cell power stage, the parameter variations of the lifetime model prove that the exponential factor of the junction temperature fluctuation is the most sensitive parameter. Besides, if a 5-out-of-6 redundancy is used, it is concluded both the B10 and the B1 system-level lifetime can be remarkably increased compared to when no redundancy is used.