Lifetime Evaluation of Three-Level Inverters for 1500-V Photovoltaic Systems

The installation cost of Photovoltaic (PV) plants can be reduced considerably by extending the maximum DC voltage from 1000 V to 1500 V (e.g., with more PV arrays connected in series). However, the increased DC voltage also presents challenges on the design and operation of PV inverters in terms of efficiency and reliability. To ensure an efficient and reliable PV power conversion, an early-stage reliability assessment is of importance in the design phase of the inverter and then the entire system. This paper, thus, evaluates the lifetime of three-level 1500-V PV inverters with respect to their thermal cycling capabilities both at the component level and system level. The evaluation is carried out through a case study on a 160-kW PV system considering the impact of voltage stress, switching frequency, and mission profile. The evaluation reveals that these factors have a significant impact on the inverter reliability, and thus affect the topology selection and the final cost of the entire PV system. More importantly, the exploration provides insights on the design of 1500-V PV systems seen from the reliability perspective.