Quasi-Static Virtual Admittance for Sequence Decomposed Grid-Forming Control

Grid-forming (GFM) control structures, consisting of active- and reactive power regulation loops followed by virtual admittances generating references for vector current controllers, offer greater flexibility and explicit control over transient over-currents by circumventing the dynamics of virtual impedance adaptation required in voltage control-based GFM controllers. Sequence decomposed implementation of the former can enable inverters to retain GFM nature under both symmetrical and asymmetrical faults. The virtual admittance can be realized adopting one of two alternatives, namely, dynamic or quasi-static implementation. In this work, comparative advantages and limitations of the quasi-static virtual admittance over its dynamic counterpart are demonstrated through analysis, simulation, and laboratory experiments in the context of sequence-decomposed grid forming control.