Grid-forming inverters (GFIs) have emerged as key enablers for establishing and stabilizing power grid voltage in inverter-dominated grids. International activities increasingly emphasize verification-oriented specifications for GFIs to support secure integration. The recent FNN note on grid-forming inverters provides structured requirements and test considerations to define and prove grid-forming behavior. However, while core properties and current limiting are addressed, it offers limited guidance for transition process between current-limiting and normal operation. This work investigates a representative GFI employing a voltage phasor-based limiting mechanism. Based on the FNN note on grid-forming behavior, we performed further experimental tests transitioning the GFI between current-limiting and normal grid-forming operation. The test framework was extended to include fault ride-through (FRT) combined with islanding, which reveals the voltage source characteristics of the GFI during limiting conditions. The employed current-limiting approach demonstrates adequate transition performance across these test scenarios. Even though, further investigations and finetuning have been identified as necessary to achieve optimised release from current limiting mode.
Unruh et al. (Sun,) studied this question.