Assessment and Experimental Validation of Grid-Forming Inverters’ Capability Counteracting Low-Frequency Oscillations

The integration of inverter-based resources (IBRs) is reshaping power grid operation by reducing system inertia, which impacts small-signal rotor angle stability and increases low-frequency oscillations (LFOs). While power-electronics-based flexible AC transmission systems (FACTSs) have been the primary solution, the shift of IBR control toward grid forming (GFM) is changing this approach. GFM control inherently provides inertia and affects small-signal stability, but implementing power oscillation damping (POD) algorithms in these inverters presents challenges, particularly regarding active-power-based ones (POD-P). Although various POD-P solutions are emerging for GFM inverters, few studies have evaluated their impact on the GFM device itself and their inherent capabilities, such as inertia and damping. This paper proposes that any design methodology should consider, besides the impact of POD controls on the grid, their effect on the properties of GFM devices. It introduces a theoretical framework using the network frequency perturbation (NFP) approach to assess this impact. Additionally, a simple POD-P control method is proposed for GFM controllers, with simplicity as its key advantage. The desired damping effect, along with the absence of impact on other frequency components, is verified through NFP analysis. The theoretical findings are experimentally validated with test bench results.