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Impact of reactive power injection outside feed-in hours on the reliability of photovoltaic inverters

Current energy paradigm of mixed renewables seems to urgently require reactive power provision at various feed-in points of the utility grid. Photovoltaic (PV) inverters are able to provide reactive power in a decentralized manner at the grid-connection point even outside active power feed-in operation, especially at night. This serves as a motivation for utilizing the PV inverters at night for reactive power compensation. Thus, a detailed analysis on the impact of reactive power injection by PV inverters outside feed-in operation on the thermal performance and also the reliability is performed in this paper. A thermal analysis based on the mission profile (i.e. solar irradiance and ambient temperature) has been incorporated, so as to determine the additional temperature rise in the components (IGBTs and diodes) outside feed-in operation for different values of reactive power injection. Consequently, the analysis enables the translation from long-term mission profiles to device thermal loading, considering the operation at night. An analytical lifetime model is then used for lifetime quantization based on the Palgrem Miner rule. Thereafter, considering the lifetime reduction of the PV inverter for different values of reactive power injection an assessment of the economic impacts is made. This analysis can be useful in choosing between conventional reactive power devices or PV inverters for injecting reactive power to the grid.