Review on Frequency Security Assessment and Coordinated Inertia Control for Low-Inertia Modern Power Systems

[Objective] The large-scale integration of high-penetration renewable energy sources（RES）and power-electronic-interfaced devices has continuously displaced the conventional synchronous generators（SG）. This transition has led to a significant reduction in the equivalent rotational inertia of modern power systems， posing unprecedented challenges to frequency security and stable operation. This paper systematically reviews and critically analyzes the state-of-the-art research on power system inertia modeling， security assessment， and coordinated control. By identifying key scientific issues and technological bottlenecks associated with low-inertia power systems， this study clarifies future research priorities and establishes theoretical foundations and technical pathways to support the secure and stable operation of highly uncertain， low-inertia modern power systems. [Methods] This paper develops a comprehensive technical framework for the security and stability analysis of low-inertia modern power systems. First， the fundamental characteristics and operational mechanisms of such systems are examined， based on which a multi-dimensional inertia modeling framework is established， including equivalent inertia modeling of synchronous generators， modeling of power-electronic-interfaced devices， and multi-timescale dynamic modeling. Second， a unified security assessment framework covering diverse operating conditions is proposed， incorporating frequency security assessment， online dynamic security assessment， and assessment under uncertainty. Finally， coordinated control strategies are developed from both spatial and multi-timescale perspectives to enable the optimal coordination of heterogeneous resources—including wind power， photovoltaic systems， energy storage， and flexible loads—thereby supporting system planning and operation. [Results] This paper systematically summarizes the complete technical framework of low-inertia modern power systems， encompassing characteristic analysis， inertia modeling， security assessment， and coordinated control strategies. The presented review deepens the understanding of operational mechanisms and security challenges in low-inertia power systems and provides valuable references for both theoretical research and engineering practice. [Conclusions] The findings offer critical technical support for ensuring the secure， stable， and efficient operation of modern power systems with high penetration of renewable energy sources.