Grid Strength and Stability Assessment Framework in Converter-Dominated Distribution Networks

Abstract

The increasing penetration of converter-interfaced resources is fundamentally changing the relationship between grid strength and system stability. Conventional metrics, such as the Short-Circuit Ratio and its variants, primarily reflect network stiffness but fail to capture control-driven and dynamic interactions introduced by inverter-based resources.This paper presents a comparative assessment of grid strength evaluation methods in converter-dominated distribution networks, focusing on grid-following and grid-forming inverters with different control strategies. A unified simulation framework is used to evaluate short-circuit-based metrics, impedance-based methods, and time-domain (EMT) dynamic responses under weak and islanded grid. The results show that SCR-based metrics remain insensitive to converter control strategies, even when system dynamics differ significantly. In contrast, impedance-based metrics provide insight into frequency-dependent interactions and reveal controller-induced differences, particularly under very weak conditions. However, these methods are limited to small-signal analysis and do not represent large-signal disturbances or operating-point effects. EMT simulations demonstrate that dynamic stability is strongly influenced by converter control and operating conditions.Based on these findings, the paper proposes a multidimensional interpretation, integrating voltage stiffness, network coupling, dynamic response, control sensitivity, and frequency interaction. The results highlight that no single metric is sufficient to characterize grid strength in converter-dominated systems, and a combined assessment approach is required.