Aging Effect Analysis of PV Inverter Semiconductors for Ancillary Services Support

Abstract

PV inverters can provide reactive power while generating active power. An ongoing microgrid implementation at Duke Energy actively engages non-utility PVs to generate/absorb reactive power in support of ancillary services to increase microgrid resiliency during extreme events. PV systems are requested to provide reactive power support: 1) in response to grid voltage variation to better regulate the local voltage; or 2) in response to utility incentives, such as following Transactive Energy System (TES) incentives. However, providing ancillary services might shorten the lifetime expectation of PV inverter semiconductors. This paper summarizes the potential impacts on a PV inverter semiconductor's lifetime when providing ancillary services. The analysis presented in this research work shows that providing reactive power support will increase the mean junction temperature and the junction temperature variation of the inverter diodes. This increased junction temperature will eventually lead to shorter diode lifetime. The lifetime estimation of semiconductors is briefly reviewed. The power losses of PV inverter semiconductors are derived as a support analysis to the junction temperature calculation. In addition, the impact of the filtering inductor on the semiconductor current distribution is discussed. The theoretical analysis presented in this research work is supported by simulation results.

Fast Quasi-Static Time-Series Simulation for Accurate PV Inverter Semiconductor Fatigue Analysis with a Long-Term Solar Profile

“…The power switches of a PV inverter could be either MOSFETs or IGBTs. The complete semiconductor switching loss and conduction loss for both MOSFET-based and IGBT-based PV inverters are summarized in Table 1 [41], where E on is the device turn-on energy, E off is the device turn-off energy, f sw is the switching frequency, I rms is the rms value of the current that flows through a semiconductor, I avg is the average value of the current that flows through a semiconductor, R IGBT is the equivalent ON resistance of the IGBTs, R D is the equivalent ON resistance of the diodes, R ds(on) is the equivalent ON resistance of the MOSFETs, V dc is the dc-link voltage, i s is the load current, V 0 is the built-in voltage of the device p-n junction, I ref and V ref are the testing current and voltage condition, respectively, provided from the device datasheets, and E rr,D is the reverse recovery energy loss of diodes.…”