Frequency-dependent modeling of grounding system in EMTP for lightning transient studies of grid-connected PV systems

The paper adopts a comprehensive modeling technique to investigate the effect of frequency-dependent characteristics of grounding system in a grid-connected photovoltaic (PV) system on the overvoltages caused by lightning strikes on the nearby overhead line. In this technique, the frequency response of grounding system is determined using an electromagnetic approach based on the method-of-moments (MoM) solutions of the governing Maxwell´s equations. To evaluate the resultant overvolatges on the key components of PV systems, the electromagnetic transients program (EMTP) is used where the grounding system is represented by an appropriate state-space model. The model is derived by approximating the frequency response of the MoM impedance matrix by a rational function based on the vector fitting method. Simulated results obtained for a typical grid-connected PV system show that when a lightning surge hits the grid, the values of overvoltages produced in the PV system can exceed those predicted by the conventional resistive model of grounding system.