Reliability prediction of PV inverters based on MIL-HDBK-217F N2

This paper initially discusses the reliability of a 250W Photovoltaic (PV) micro inverter. Using the bill of materials the reliabilities of the main, gate drive, power supply, current and voltage sensing and microprocessor circuits were investigated, and the failure rate and Mean Time Between Failure (MTBF) calculated. The sum of component failure rates equals the complete PV micro inverter failure rate. To account for temperature effects the component failure rate was calculated for each inverter operating temperature, and multiplied by the percentage occurrence of this operating temperature to obtain a weighted failure rate. A similar procedure was used to calculate the failure rate for the main circuits of a 4.6kW & a 4.5kW multi-string inverter. All calculations are based on MIL-17F N2 method.