Grid-Forming Dynamic Stability under Large Fault Events – Application to 100% Inverter-based Irish Power System

System stability is investigated for a future Irish grid consisting entirely of GFMIs under three-phase fault conditions with the inverters placed at existing locations for large-scale conventional generation. Electromagnetic transient (EMT) simulations showed that a 100% GFMI system, employing either droop control (or virtual synchronous machine), dispatchable virtual oscillator control, or a mix of both, under a combination of virtual impedance (VI) and scaling current saturation limiting control, is robust against 3-phase faults, with consistent performance being achieved, despite variations in fault location or inverter control methods. Freezing GFMIs virtual angular speed during the fault, for both VI and current scaling approaches, system transient stability is greatly enhanced. Time domain simulations also show that when active or reactive current prioritisation current saturation controls are applied that GFMIs can introduce large, high-frequency resonance oscillations, but a scaling-down current saturation approach can help to mitigate such problems by generating smoother current references.