Junction Temperature Control for Lifetime Extension of Multi-functional Photovoltaic Inverters

The provision of reactive power compensation and phase balancing services by photovoltaic (PV) inverters is considered an essential functionality for enhancing the power quality and efficiency of distribution grids. However, the provision of such grid services can increase the power losses of PV inverters in an asymmetric way (i.e., each inverter leg experiences different power losses) which is primarily attributed to the unequal current flows at each leg of a three-phase PV inverter. This can cause a different temperature rise in each switching device, leading to a reduction of the overall lifetime of the inverter. This paper investigates the potential improvement of PV inverters reliability with a junction temperature control while providing phase balancing and reactive power compensation. The proposed junction temperature control limits the provision of ancillary services, when needed, to ensure that the thermal stress at each switching component is kept within the desired levels. As a result, the new inverter controller enables a multi-functional operation for providing additional services while reducing the impact on its lifetime degradation. Experimental tests are carried out to demonstrate the performance of the junction temperature control during ancillary services provision. Finally, a techno-economic framework is developed to analyze the financial benefits from the provision of ancillary services by considering a long-term reliability analysis of the switching devices and the proposed junction temperature limit controller.