Derivative-Free Grid Inertia Estimation Via Frequency Ramp Test

With the significant decline in grid inertia over the past decade, accurate inertia estimation has become crucial to prevent frequency instability caused by insufficient inertia. Conventional measurement-based methods estimate grid inertia using the rate of change of frequency (RoCoF) during power step (P-Step) tests, where RoCoF is calculated using the derivative of the measured frequency. However, since derivative operation is highly sensitive to noise that is inevitably present in measured frequency, these methods cannot accurately estimate inertia and may even be invalid in high-noise environments. To address this issue, this paper proposes a derivative-free grid inertia estimation method that replacesP-Step test with frequency ramp (f-Ramp) test. Inf-Ramp test, the frequency varies in a ramp profile by regulating the power of converter-based sources. A key finding is that, unlikeP-Step test, the grid inertia power duringf-Ramp test is constant and its magnitude equals the constant component of converter power. Based on this characteristic, the proposed method estimates the grid inertia utilizing the aforementioned constant component instead of RoCoF, avoiding noise-sensitive derivatives. Then, the detailed procedure is introduced. Finally, the proposed method is validated through full-power hardware-based experiments, overcoming the limitations of simulation-based verification common in existing studies.