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.
Highlights
Solar photovoltaic (PV) integration requires power electronic inverters to interface with the power grid
The power losses of PV inverter semiconductors derived in this paper provide a support analysis for the calculation of junction temperature
The lifetime model formulates the inverter semiconductors’ thermal stress under the scenarios where the PV inverter is engaged in reactive power support. Both the analysis and the simulation results show that the average conduction loss of inverter diodes increases when the output current pf decreases
Summary
Solar photovoltaic (PV) integration requires power electronic inverters to interface with the power grid. Many literature have reported that the inverter’s power electronic devices and passives (capacitors) have shorter lifetime compared to its associated PV panels [1], [2]. For example in a PV system, the lifetime of the PV panels is normally warrantied at 20–25 years, whereas the PV inverter lifetime is usually less than 15 years [1]. The utility power industry usually expects a long lifetime of the inverters so that the inverters could retire from the power grid at the same time as the whole PV system [4]. An industry-wide survey presented in [4] indicates that semiconductors and capacitors are the most vulnerable components that lead to inverter failure. The power losses of semiconductors and capacitors are dissipated as heat, and this heat dissipation increases the mean junction temperature and the temperature variation of semiconductors and capacitors
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