Current Limitation Strategy For Grid-Forming Converters Under Symmetrical And Asymmetrical Grid Faults

The potentials of grid-forming (GFM) converters in stabilizing a power system with high penetration of power electronics-based generation have been recently investigated. Due to their intrinsic behaviour of voltage source behind impedance, a crucial aspect of any GFM converter control strategy will be the handling of fault-ride through (FRT) scenarios. This paper proposes a FRT strategy for GFM converters, which respects the converter hardware limitations (i.e. current limitations) even under sever fault conditions, while maintaining GFM behavior before, during, and after the fault. The presented strategy addresses both symmetrical and asymmetrical faults, and is compliant with recently proposed draft grid codes requirements published by the British system operator NGESO. The issues related to FRT of GFM converters are first discussed in detail, and a comprehensive overview on the solutions proposed in the literature is reported. Then a proper strategy is presented, and its effectiveness is demonstrated by means of simulations and Power-Hardware-in-the-Loop (PHIL) measurements in a laboratory environment.