Resilient Operation of Grid-Forming Inverters under Large-scale Disturbances in Low Inertia Power System

The future power grid is transitioning toward a low inertia power system due to the displacement of synchronous generators (SG)-based generation sources and incorporating inverters-based renewable energy resources. Heterogeneous grid-forming inverters (GFMIs) are expected to be dominant sources in the power generation mix due to several benefits that are inherited in this inverter control. However, these GFMIs impose different transients on the power grid that did not exist in the conventional power grid. The effect of this heterogeneity on the dynamic behavior of such power grid with a fleet of GFMIs becomes more significant under large-scale disturbances such as short circuit faults. Particularly, because of the noncoherent and heterogeneous dynamic behavior of GFMIs in the presence of the conventional overcurrent protection schemes posing several challenges to the resiliency of a power grid during a fault and in a postfault state. To improve the resiliency of the power grid with heterogeneous GFMIs during these conditions, a coherency enforcement scheme among heterogeneous GFMI is proposed. This ensures a coherent transition of GFMIs from the normal to fault-ride-through mode and from the fault-ride-through mode to normal condition when the fault is cleared. Moreover, the proposed improvements in GFMI control prevent the excessive change/acceleration in the voltage angle of GFMIs that prevents the loss of synchronism, improves the dynamic behavior of GFMIs, and ensure seamless operation under large-scale disturbances, resulting in enhancing resiliency of power grid. These claims in the resiliency enhancements for a power grid dominated with heterogeneous GFMIs under large-scale disturbances are validated via hardware-in-the-loop experimental case studies.