Experimental Assessment of Inverter‐Based Frequency Support via Transient Frequency–Power Dynamics

The increasing penetration of inverter-based resources fundamentally changes the nature of frequency stability in low-inertia power systems. Frequency support becomes predominantly transient-dominated and is governed by the dynamic interaction of converter control structures rather than by aggregate inertia alone. While grid-forming (GFM) inverters are widely regarded as essential for fast frequency support, the dynamic limitations and shaping potential of grid-following (GFL) control architectures remain insufficiently understood. This paper presents a systematic and experimentally backed comparison of inverter-based frequency support concepts based on their transient frequency–power dynamics. GFL droop control, GFM droop control, and Virtual Synchronous Machine (VSM) control are implemented on identical inverter hardware using a common inner control structure. The dynamic mapping from frequency deviation to active power injection is characterized through laboratory experiments and low-order system identification. In addition, an H∞-based matching controller is introduced to shape the closed-loop frequency–power dynamics of a GFL inverter to emulate GFM behavior. The results demonstrate that classical GFL droop control exhibits delayed power responses due to measurement-based synchronization and cascaded tracking loops, leading to deeper frequency nadirs in weak grids. GFM strategies enable immediate power injection and explicit damping, with inertia and damping acting as complementary tuning parameters. Crucially, the experiments show that GFL inverters equipped with H∞ matching control can reproduce key GFM frequency–power characteristics, including rapid initial power injection and substantially improved frequency nadir, in both strong-grid and weak-grid scenarios. These findings indicate that fast frequency support is not inherently tied to the GFM or GFL classification of an inverter, but to the closed-loop frequency–power dynamics achieved by its control structure. Accordingly, a strict dichotomy between GFM and GFL concepts is not sufficient to assess frequency-support capability.