Analytical Framework for Assessing Effective Regional Inertia

TL;DR

This paper introduces a topology-aware analytical framework for assessing effective regional inertia, accounting for system topology, inertia distribution, and virtual inertia contributions, to improve frequency stability analysis.

Contribution

It presents a novel, explicit formulation of regional inertia that extends classical coherency theory to include network partitioning and virtual inertia effects.

Findings

Effective inertia varies significantly across regions.

Integration of inertial devices does not always enhance frequency response.

The proposed metric improves understanding of local inertial contributions.

Abstract

This paper proposes a novel formulation of effective regional inertia that explicitly accounts for both system topology and the spatial distribution of inertia. Unlike traditional approaches that model a region as an aggregated machine with an equivalent inertia, the proposed metric provides a topology-aware representation. The methodology builds on an analytical framework that extends classical slow coherency theory to address network partitioning and regional frequency stability. Based on these partitions, we develop a systematic procedure to evaluate the effective inertia of each region, enabling a more accurate interpretation of local inertial contributions, including those from virtual inertia provided by inverter-based resources (IBRs). Case studies on the IEEE 39-bus and 68-bus systems demonstrate that the integration of inertial devices does not uniformly improve system frequency response, underscoring the importance of the proposed metric for effective regional inertia assessment.