Assessment of Post-Fault Voltage Recovery in IBRs-Dominated Grids: Evaluating the Role of Grid-Forming Converters

Abstract

Conventional Synchronous Generators (SGs) are increasingly being replaced by Inverter-Based Resources (IBRs) for integrating Renewable Energy Sources (RESs). However, this transition introduces significant challenges, as most existing IBRs employ Grid-Following (GFL) converters that depend on a strong grid connection for stable operation. Consequently, their ability to provide dynamic voltage support and maintain post-fault voltage recovery might be limited in IBR-dominated grids. To address these issues, grid-forming (GFM) converters have emerged as a promising alternative. Unlike GFL converters, GFM units can emulate SG behaviour by autonomously establishing grid voltage and frequency, thereby enhancing both steady-state performance and dynamic response during disturbances. This study investigates the potential role that GFM converters may play in improving dynamic voltage support and post-fault voltage recovery in IBR-dominated grids. It first examines post-fault voltage recovery in conventional SG-based systems, then evaluates various IBR penetration scenarios, with low, medium, and high penetrations of IBRs based on both traditional GFL and emerging GFM converters, integrated to replace large and central SGs. Finally, a correlation-based sensitivity analysis is introduced to systematically quantify the relationship between fault-induced voltage nadir and voltage recovery speed across network locations and penetration levels of IBRs. Through simulations and analysis using a modified IEEE 9-bus test system modelled in DIgSILENT PowerFactory, the study demonstrates the vital role of GFM converters in ensuring robust post-fault voltage response and overall grid stability in renewable-rich power systems.