Comparison of reliability impacts of two active power curtailment methods for PV micro-inverters

The future generation of solar PV inverters will have to be equipped with new grid supporting functionalities. One of them is the active power curtailment (APC) for overvoltage prevention. New functionalities can be challenging from the design-for-reliability aspect. This is especially true for micro-inverters, due to their outdoor application and more extreme environmental conditions. In this paper, two APC designs are considered and their impact on component reliability is predicted using 217Plus™ empirical method. The analyzed components are DC bus capacitors, DC-DC MOSFETs and an AC protection relay. The study reveals that APC can decrease the failure rate of MOSFETs and capacitors. Depending on the selected APC method the capacitor failure rate reduction is either 6% or 54%, but the latter benefit comes with a trade-off for a high failure rate increase of the AC relay. The failure rates are not significant from warranty perspective, but indicative enough for making preliminary design-for-reliability recommendations.