Estimation of the equivalent inertia of grid-forming and grid-following inverter-based resources

As inverter-based resources (IBRs) become increasingly prevalent in power systems, the dynamic behavior of these systems is evolving due to shifts in system inertia characteristics. With the gradual replacement of synchronous generators by IBRs, the constant inertia traditionally supplied by generators is now being replaced by control-emulated inertia from IBRs. Depending on their control strategies, IBRs may provide time-varying inertial support after disturbances, even when operating with a fixed inertia parameter. This thesis introduces the concept of “equivalent inertia” to quantify the collective inertial response of IBR controls by comparing it to the inertia of a fictitious synchronous generator with an inertial response identical to the IBR. An inertia estimation method is then proposed, based on a swing equation-derived function that utilizes bus measurement data. A key advantage of this method is its applicability to both synchronous generators and IBRs without relying on device-specific mathematical models. Additionally, an accurate estimation indicator is proposed to indicate the estimation accuracy. The proposed method is first validated using synchronous generators and subsequently applied to estimate the inertial support of grid-following and grid-forming IBRs. Finally, these estimations are verified through frequency response simulations conducted on the IEEE 14-bus and NPCC 140-bus systems.