A Feasibility Study of Offerings for a New-Type Ancillary Service Market: System Strength Market

In power systems with high renewable energy penetration, System Strength services have become a critical ancillary service type for maintaining grid stability. Traditional ancillary service markets (e.g., frequency regulation, peak shaving, reserve power) primarily address energy balance, whereas system strength services focus on fault level, virtual inertia, and voltage support to compensate for reduced system strength caused by decreased synchronous generators due to inverter-based resource (IBR) integration. This study extends the ancillary services market into the system strength domain to enhance grid resilience under large-scale IBR integration. It aims to design a comprehensive market mechanism framework positioning power electronic devices (such as Grid-Forming Inverters GFL and Virtual Synchronous Machines VSM) as independent market participants, enabling a shift from “passive integration” to “active provision” of services. This paper is a review that systematically organizes and evaluates the latest research trends and challenges concerning system strength, an indicator for assessing power system stability, against the backdrop of increasing inverter-based resources (IBRs) accompanying the rapid expansion of renewable energy sources. First, it organizes representative indicators used domestically and internationally to quantify system strength, such as short-circuit capacity, impedance characteristics, and interaction indicators, along with their application conditions. Next, it examines the impact of IBRs on voltage stability, synchronous performance, and transient stability under grid conditions with high IBR penetration, comparing the limitations of each metric and the characteristics of the evaluation results. Furthermore, it summarizes the application effects and challenges of recently proposed weak grid countermeasure technologies (advanced inverter control, virtual synchronous generator control, grid reinforcement methods, etc.). Through this review, it demonstrates the importance of standardizing system strength evaluation, integrating metrics, and improving model accuracy for future high-IBR grids, and proposes comprehensive research challenges.