The cause of sub-cycle overvoltage: Capacitive characteristics of solar PVs*

In 2017 and 2018, large-scale solar photovoltaic (PV) tripping events occurred after transmission grid disturbances. Sub-cycle overvoltage is identified as the main cause that the PV inverters' protection systems initiated tripping actions. According to the reports from North American Electric Reliability Corporation (NERC), overvoltage is more severe at the PV inverter buses compared to the point of measurement (POM). Mechanism analysis of such a feature is an open research problem in the NERC community. This paper fills the gap. The goal of this paper is to explain why inverters may experience more severe overvoltage compared to the POM bus, which usually has shunt compensation installed. Through circuit construction with inverter control included, this paper will analyze and demonstrate the role of inverter control in aggravating overvoltage due to its capacitive nature in the subcycle dynamic range. While this nature is well known to the power electronics community, the current paper connects the dots to demonstrate how the capacitive nature of inverters can influence solar PV operation in a grid. A quantitative analysis is presented to explain the overvoltage mechanism.