Grid-forming requirements based on stability assessment for 100% converter-based Irish power system

The fault response of a 100% converter-based system can be significantly different to that of a synchronous generator-based system, considering the lower capacity headroom, but flexible control capability, of power electronic converters. The system response is investigated for an Irish grid under balanced three-phase faults comprising of 100% converter-based generation: grid-forming (GF) and grid-following (GL). Electro-magnetic transient (EMT) simulations show that a system consisting only of GF converters (all droop control, all dispatchable virtual oscillator control, or a mix of both) is robust against three-phase faults, with little variation in performance, despite the fault location or choice of GF control methods. However, the rating and location of GF converters are critical to operating the grid securely in the presence of both GF and GL converters. Assuming that individual converter bus nodes are either GF or GL, a minimum GF requirement (by capacity) is found to be 37–40%, with these GF converters located close to the major load centres. Assuming instead that individual generation nodes consist of a mix of GF and GL converters, it is found that the GF requirement can be relaxed by 8–10%.