A Review of System Strength and Inertia in Renewable-Energy-Dominated Grids: Challenges, Sustainability, and Solutions

The global shift towards renewable energy sources (RESs) presents significant challenges to power grid stability, particularly in grids with a high penetration of inverter-based resources (IBRs). The shift to RESs is critical to improve planetary health; however, grids must remain reliable and affordable throughout the transition to ensure economies can thrive and critical infrastructure remains secure. Towards that goal, this review introduces the issues of declining system strength and inertia in such grids, illustrated by case studies of curtailment measures employed by system operators in the deregulated electricity markets of Australia, Ireland, and Texas. In these high-IBR markets, curtailment has become essential to maintain system security. This paper presents the current mitigation strategies used by system operators and discusses their limitations. In addition, the paper presents a comprehensive review and analysis of current research on system strength and inertia estimation techniques, grid modelling approaches, and advanced inverter control, with a particular focus on virtual inertia. Future research directions and recommendations are outlined based on the identified gaps. These recommendations are intended to minimise system operator intervention and RES curtailment while maintaining reliable and affordable grid operation. The insights presented in this paper provide a framework to guide system operators, researchers, and policymakers toward enhancing grid stability while targeting 100% RES.