Effect of Reactive Power on Photovoltaic Inverter Reliability and Lifetime
Ramanathan Thiagarajan, Adarsh Nagarajan, Peter Hacke, Ingrid Repins
National Renewable Energy Lab, Golden, CO, United States

For predicting the reliability and lifetime of Photovoltaic (PV) inverters, thermal cycling is considered the most important stressors in the inverter system. To realize this, a detailed electrothermal model of the PV inverter was developed along with the controllers. The model was verified by developing an in-house inverter, which was placed inside a thermal chamber to verify the losses and temperature rise within the system at various temperatures. After the verification of the model, a reduced order model of the inverter was implemented which can translate the mission profile of ambient temperature and solar irradiance into load profile of junction temperatures of the switches. The estimated junction temperature data was used to identify the reliability indices and predict the useful lifetime of the inverter system. After developing the models to predict useful lifetime of the system, the impact of reactive power on the overall reliability of the system was studied. Experiments show that lifetime and reliability of the inverter decreases as the operating power factor decreases from unity. The results are presented and discussed here.

Area: Sub-Area 10.5: Reliability and Safety of Power Electronics and PV Systems (Joint between Topic Areas 9 and 10)