Frequency-Averaged Grid Impedance Metric for Identifying Weakest Buses in Power Electronics-Dominated Systems

The increasing penetration of Power-Electronic Interfaced Resources (PEIR) in power systems poses challenges to stability and requires a reevaluation of conventional methods for assessing system strength as a proxy for low risk of inverter interaction. This paper introduces a novel metric, the Frequency Averaged Grid Impedance (FAGI), specifically designed to capture the behaviour of PEIR under various control schemes and to support decision-making. Its performance is compared to the widely used Equivalent Short Circuit Ratio (ESCR), as implemented in RTE’s operational tool. A 4-VSC system is analysed considering different study cases. Dynamic simulations are conducted to validate the rankings provided by each metric, showcasing the limitations of SCR-derived approaches.