Implementation Options and Trade-offs in Emergency Generation Shedding to Mitigate Inverter Oscillations in Low-Voltage Distribution Networks

The Emergency Generation Shedding (EGS) mechanism is a last-resort measure applied by curtailing distributed solar generation during periods of high photovoltaic (PV) generation and low demand when the system is at risk of losing system security. EGS aims to force disconnection of legacy distributed PV (DPV) systems by temporarily raising the zone substation voltage setpoint. While EGS has proven effective in supporting the power grid during critically low demand periods, reports indicate that it can induce voltage and power oscillations from inverters cycling between disconnection and re-connection, which may be triggered by the steep increase in voltage setpoint. This oscillatory effect is worse in low-voltage (LV) networks where mutual inductance between phases can propagate these oscillations even in systems not connected to the same phase. This study investigates EGSinduced oscillations in unbalanced 3-phase distribution systems and assesses different settings options to gradually step up voltage setpoint in order to minimise the occurrence of these oscillations. Using power flow simulations on a representative Australian low-voltage network model, we analyse how different transformer voltage step-up tap scenarios can influence the number of inverter switch-offs and mean aggregated power generation. The results indicate that while the power generation shed remains relatively consistent across different tapping sequence scenarios, there is a significant variability in the resulting number of inverter tripoffs. In conclusion, a gradual voltage rise strategy for EGS can substantially reduce inverter disconnection-reconnection oscillations as compared to those obtained after the application of a single step voltage raise approach.