Transient Stability Comparison of Grid-Forming and Grid-Following Inverter-Based Resources

Modern power systems are increasingly operating at high penetration levels of inverter-based resources (IBR). As IBR penetration increases and synchronous generators are decommissioned, fundamental operational and stability challenges arise from IBR/IBR and IBR/grid interactions under transient and fault conditions. In this paper, the transient stability of state-of-the-art grid-following (GFL) and grid-forming (GFM) IBRs are analyzed for large signal transients, i.e., three-phase zero impedance faults and large load steps, for different IBR penetration levels, fault locations, and a variety of GFL and GFM controllers with various fault-ride-through/current limiting techniques. A 3 MVA/34.5 kV four-bus radial power system configuration is utilized as the base system to study the aforementioned large signal transients using a Matlab/Simulink simulation environment. Herein, and bounded to the specific parameters and use cases analyzed, this work highlights the large signal transient performance degradation with IBR penetration increase, especially for GFL IBRs. Conversely, similarly rated and tuned GFM IBRs showcase significant performance improvements in frequency response, which suggests that the implementation of such controllers may improve the operability of high-IBR penetration systems.