Bridging control paradigms: a state-of-the-art review of grid-forming BESS-STATCOMs for enhanced power system stability

Power-electronic inverters play a central role in modern power systems due to the increasing penetration of renewable energy sources such as solar photovoltaics, wind generation, and battery energy storage. While this transition supports decarbonization goals, it also introduces significant challenges related to system inertia reduction, voltage and frequency stability, control interactions, and cybersecurity. Conventional grid-following (GFL) inverters rely on external grid references and lack of inherent inertia, whereas grid-forming (GFM) inverters can autonomously establish voltage and frequency, emulating key characteristics of synchronous generators. This paper presents a comprehensive state-of-the-art review of battery energy storage system–static synchronous compensators (BESS-STATCOMs) operating in both GFL and GFM modes but the primary focus of the paper is to bring out the efficacy of BESS-STATCOM operating in GFM. The review systematically compares control philosophies, stability characteristics, grid-interaction mechanisms, implementation challenges, cybersecurity considerations, and economic and environmental impacts. By synthesizing recent high-impact research and evolving grid-code requirements, the paper identifies unresolved challenges and emerging research directions for inverter-dominated, low-inertia power systems. The presented analysis provides practical insights for researchers, utilities, and system operators seeking resilient and stable deployment strategies for BESS-STATCOM technologies. The core contribution of this review is a unified, state-of-the-art synthesis of Battery Energy Storage System–STATCOM (BESS-STATCOM) technologies operating in both Grid-Following (GFL) and Grid-Forming (GFM) modes, with particular emphasis on the emerging role of GFM control in low-inertia, weak-grid, and inverter-dominated power systems.