Reliability assessment of photovoltaic inverters considering volt/var control

This paper investigates the impact of the volt/var control strategy on the lifespan of grid-connected photovoltaic (PV) inverters. With the increasing penetration of PV systems in modern distribution networks, volt/var control has become a cornerstone of grid codes to enhance voltage regulation and grid stability. This strategy enables PV inverters to inject or absorb reactive power dynamically according to the voltage conditions sensed by each inverter at the point of common coupling to mitigate intense voltage fluctuation. However, while volt/var control improves grid performance, it imposes additional operational demands on PV inverters, affecting their thermal performance, reliability, and lifespan. The study highlights that the degradation of PV inverters is significant under volt/var control and unfairly distributed, depending on the location of the installed inverter in the distribution network. For investigating the lifetime of PV inverters, a comprehensive long-term lifetime model is developed, incorporating thermal cycling and electrical stress caused by real and reactive power. The model quantifies the cumulative degradation of key inverter components under volt/var support, which is highly affect by the installation location of each PV inverter. The findings underline the need for modifications to conventional volt/var strategies to ensure efficient voltage control and fair degradation across inverters.