Voltage Support Capability of Grid–forming Inverters under Significant Load Disturbances

The rapid increase in the integration of intermittent renewable energy sources into the distribution grid impacts grid voltage and frequency stability. These inverter– based resources (IBRs) replace synchronous generators which provide system inertia to maintain system stability under grid disturbances. Grid–forming (GFM) inverters can play a significant role in mitigating the problems of large–scale integration of renewables and distributed IBRs. The impacts of increased integration of the GFM–based resources in the network voltage profile have been analyzed using a modified IEEE–9 bus system with three GFM inverters. Simulation studies have investigated the (1) impact of increased penetration of GFM inverters on voltage profile, (2) maximum system loading with multiple GFM inverter combinations, (3) improvement of system voltage profile by the appropriate selection of the GFM inverter control strategies, and (4) power– sharing capability among GFM inverters in different control schemes. Simulation results have identified that the maximum system loading could be increased by 13.33% without violating the low voltage limit of 0.94 p.u.. A 29% load increase will violate the low voltage limit, however, 3–GFM control at voltage regulation (VR) mode could bring the voltage back to the acceptable range.