Stability of distribution networks under high penetration of inverter-based resources: highlight of novel interactions

The integration of Renewable Energy Sources (RES) through Inverter-Based Resources (IBRs) is transforming power systems from synchronous machine (SM)-dominated networks to low-inertia, decentralised systems. This shift introduces stability challenges, as IBRs bring fast dynamics that disrupt traditional behaviours. Coupled with reduced inertia and strength in upstream transmission networks, distribution networks with high IBR penetration face novel dynamic interactions. This study examines these interactions, highlighting two primary stability concerns: slow dynamics, exemplified by instabilities arising from high droop gains in Grid-Forming (GFM) IBR units, and fast dynamics, illustrated by the interplay between GFM inner current loops, network dynamics, and SG stator flux dynamics. Using advanced Electromagnetic Transient (EMT) and linearised models, the study highlights how high droop gains and slower current controllers exacerbate instability. Mitigation strategies like adjusting GFM filter capacitance or line R/X ratios are proposed, offering DSOs critical insights for planning and managing high IBR integration.