Revisiting the X/R Ratio as an Operating-Regime Descriptor in Inverter-Dominated Power Systems

The electrical characteristics of modern power systems have been altered fundamentally by the increasing penetration of inverter-based renewable energy sources (IB-RES). Recent studies have treated the reactance-to-resistance (X/R) ratio implicitly within network models, while emphasising reduced inertia, grid-forming control, and short-circuit ratio (SCR). This letter argues that, in the IB-RES power system, the X/R ratio plays a structurally different role than in conventional power grids, where synchronous generators dominate. Through analytical reasoning and representative quantitative observations, it is shown that variations in X/R ratio alone, under identical SCR and control settings, can lead to qualitatively different stability margins, control coupling, and impedance-based protection behavior. Thus, a generalized inverter-grid interface model is used to isolate impedance-driven effects from topology-specific artifacts. The results highlight the importance of explicitly accounting for the X/R ratio when interpreting inverter behavior under weak and resistive grid conditions.