Grid-Forming Controls Outperform Grid-Following for Large-Scale Energy Storage, Says IEEE Study

A new study published in IEEE TRANS POWER SYSTEMS (2026) by Qiang Fu, Siqi Bu, Yang Wang, and Mingyu Yan analyzes small-signal stability of centralized energy storage systems (CESS) under two dominant control paradigms: grid-following (GFL) and grid-forming (GFM). The researchers used a virtual damping method to simplify high-order dynamics and focus on dominant oscillation modes. Their damping analysis reveals that single-type control systems exhibit dynamic superimposition — as the number of storage units increases, GFM-CESS damping improves, while GFL-CESS damping decreases. This makes GFM controls inherently more stable for large-scale deployments.

The study further examines damping sensitivity to bidirectional power flow and control loops. GFM-CESS is more sensitive across all control loops, while GFL-CESS is primarily sensitive to the d-axis loop. This sensitivity profile gives GFM an edge for large-scale integration, but also imposes a critical limitation: GFM-CESS struggles in scenarios with significant power reversal. For hybrid systems combining both controls, the authors warn that the GFM ratio must be constrained to prevent modal resonance between GFL and GFM units, which could cause instability. The findings stress that GFM adoption should be scenario-aware rather than maximized. Conclusions are validated through modal analysis and time-domain simulations.