Response of low voltage networks with high penetration of photovoltaic systems to transmission network faults

The installed capacity of photovoltaic (PV) systems connected to low voltage (LV) networks in Germany has increased to more than 25 GW. Current grid codes still mandate these PV systems to disconnect in case of voltage dips below 0.8 p.u. The resulting response of LV distribution systems with high penetration of PV systems to faults in the transmission network is investigated for an integrated power system model that comprises all relevant voltage levels. Sensitivity studies with respect to the pre-fault power flow, various steady state and fault ride-through (FRT) control modes were performed. Our simulations for a realistic 2022 scenario show that a lack of FRT capability can cause the distribution system load to increase by 35-70 % of its peak value. It was found that for under-excited operation of PV systems prior to the fault, an overvoltage can occur post-fault at some busbars in the distribution system. Therefore, we conclude that new LV-connected PV systems and other DG installations should be requested to perform FRT.