Reliability of Microinverters for Photovoltaic Systems: High-Temperature Accelerated Testing with Fixed and Cyclic Power Stresses

This paper presents an extended, accelerated reliability evaluation of forty microinverters, module-level power electronic (MLPE) units for photovoltaic (PV) modules. The forty microinverters were stressed at two static temperatures (65 degrees C and 75 degrees C) with two input power profiles (fixed and cyclic power). These power profiles were employed to replicate field-use conditions closely. The accelerated testing was performed for an extended duration (over a period of 15,000 h) to determine the acceleration factor and estimate the service life of microinverters in field-use conditions. Electrical performance and thermal data were continuously monitored during the experiment for all the microinverters. The accelerated stress testing had no failures even after 15,000 h of operation. Using the Arrhenius life-stress model along with average field-measured temperature and military handbook-based analysis, it was estimated that the microinverters should be able to survive for 24-48 years during their service life in field conditions, with a reliability of 74%, having a lower one-sided confidence bound of 95%, obtained using the classical success run approach. Moreover, the lifetime of microinverters was statistically analyzed using a Weibull distribution model. Weibull slope factors were used to estimate a range of characteristic lifetime periods and the reliability of the microinverters with a 95% lower one-sided confidence limit, demonstrating a similar or even exceeding the lifetime of the associated PV modules of 25 years.