Impedance-based stability analysis and comparison of different grid-forming control approaches

This paper presents an impedance-based analysis and comparison of three grid-forming control approaches derived from the synchronous generator swing equation and implemented for an E-STATCOM in EMT simulations. The study considers a synchronverter and two virtual synchronous machine concepts that differ in their virtual stator representation, namely virtual admittance and virtual impedance. The results show that the virtual-admittance-based approaches exhibit very similar dynamic and impedance characteristics, whereas the virtual-impedance-based approach deviates significantly. In addition, the effect of integrating a notch filter into the virtual admittance control structure is analyzed by evaluating the resulting frequency-dependent impedance. Finally, all three control approaches are assessed with respect to their compliance with German grid code requirements.