Evaluating the Equivalent Inertia of Grid-Following and Grid-Forming Inverter-Based Resources

The increasing prevalence of inverter-based resources (IBRs) is creating changes in the dynamic behaviors of power systems. Depending on the type of control, IBRs can exhibit time-varying inertial support following disturbances, even when using a fixed inertia parameter. This paper introduces the concept of “equivalent inertia”, which measures the collective inertial support dependent on the controls, using a fictitious synchronous generator to match the response. Next, an inertia estimation method is proposed by constructing a swing equation-based estimation function utilizing bus measurement data. A major advantage of the proposed method is its applicability to synchronous generators and IBRs without requiring device mathematical models. Moreover, an accurate estimation indicator is proposed to indicate when the estimation is accurate. The estimation method is validated using synchronous generators and then used to estimate the inertial support of grid-following and grid-forming IBRs. Finally, the estimations are validated by frequency response simulations using small and large test systems.