Impedance-Based Stability Analysis of IBR Integrated Power Systems Using Advanced PowerFactory Impedance Scanning

The increasing penetration of Inverter-Based Resources (IBRs), particularly grid-forming inverters (GFMs), necessitates robust dynamic stability assessment in modern power grids. Traditional eigenvalue methods face limitations in converter-dominated systems due to proprietary control data, making impedance-based stability analysis a more suitable alternative by leveraging measurable terminal frequency responses. This study investigates the small-signal stability of GFM-IBRs in a modified IEEE 9-bus system, systematically replacing synchronous generators with Virtual Synchronous Machine (VSM)-based GFMs. Electromagnetic Transient (EMT) simulations in DigSilent PowerFactory, utilizing frequency-domain perturbation, extracted frequency-dependent impedance characteristics. Stability was evaluated using Nyquist plots under the Generalized Nyquist Criterion (GNC) for single and multiple IBR configurations across various operating conditions. Results consistently showed system stability with s table Nyquist margins, even with lower margins under reduced grid strength and stressed operating points. The analysis highlighted the operating point dependency of GFM impedance and the effective damping provided by GFMs against inherent grid resonances (300-800 Hz). Time-domain validation supported these frequency-domain predictions. This work establishes a reliable impedance-based framework for GFM stability assessment, paving the way for future studies on multi-inverter controls and larger-scale networks.