Impact of Inverter Dynamics during System Restoration Period on Protection Schemes in Grid-Connected Solar PV Systems

Abstract

The growing penetration of renewable resources such as wind and solar into the electric power grid through power electronic inverters is changing the grid dynamics and challenging grid protection. Due to the advanced inverter control algorithms, the inverter-based resources present fault responses different from conventional generators, which can fundamentally affect the way that the power grid is protected and thus is challenging grid protection engineers. This paper studies inverter dynamics during the system restoration period and their impact on protection schemes in a grid-connected solar photovoltaic (PV) system following grid disturbances. To this end, the solar PV system with a detailed inverter model that consider inverter switching dynamics along with inverter blocking and deblocking functions are constructed for the hardware-in-loop simulation based on a real-time digital simulator (RTDS). It is found that undesired transient events such as three-phase overvoltage and overcurrent as well as negative sequence current may occur after the inverter is deblocked to reinject energy into the system during the restoration period following a grid disturbance, especially when the system is under weak grid conditions. The undesired transient events may lead to misoperation of instantaneous overcurrent and negative sequence overcurrent protection schemes.