Reliability: A New Approach in Design of Inverters for PV Systems

Several surveys of single-phase inverters for residential installations have been reported recently. However, the surveys are aimed at establishing a classification of the topologies reported, and do not explicitly take into account the reliability. This paper presents a reliability-oriented survey of the inverter topologies reported in the literature. The survey is aimed at finding out how well the designers have solved the reliability issue. As such, it complements previous surveys focused at issues such as maturity of the technology. Also a reliability prediction of four photovoltaic systems is presented: a two-stages system, a three-stages one, and two integrated topologies, one with a boost-inverter, and the second with a buck-boost inverter. The goal is to identify the most failure prone components, and the stress factors with the highest contribution to the failure rate. In all cases, it was found that the transistors are the most vulnerable components, and that the dominant stress factor is related to the temperature. It was also found that the reliability can be improved if the switching devices are overrated, but only to a certain level, and using too large transistors can be counterproductive