Defining humidity test duration for microinverter reliability assessment: A physics-of-failure approach

Microinverters are module-level power electronic (MLPE) systems that are expected to have a service life more than 25 years. The general practice for providing assurance in long-term reliability under humid climatic conditions is to subject the microinverters to `damp heat test' at 85°C/85%RH for 1000hrs as recommended in lEC 61215 standard. However, there is limited understanding on the correlation between the said `damp heat' test and field conditions for microinverters. In this paper, a physics-of-failure (PoF)-based approach is used to correlate damp heat test to field conditions. Results of the PoF approach indicates that even 3000hrs at 85°C/85%RH may not be sufficient to guarantee 25-years' service life in certain places in the world. Furthermore, we also demonstrate that use of Miami, FL weathering data as benchmark for defining damp heat test durations will not be sufficient to guarantee 25 years' service life. Finally, when tests were conducted at 85°C/85%RH for more than 3000hrs, it was found that the PV connectors are likely to fail before the actual power electronics could fail.