Nonlinear Frequency-Domain Stability Criterion for Three-Phase Grid-Following Inverters

In addition to the synchronization unit and weak grid, the current control also significantly affects the transient stability of the grid-following inverters (GFIs). Taking into account the dynamic interaction of multiple loops, this article proposes a nonlinear frequency-domain stability criterion, also called absolute stability criterion (ASC), for three-phase GFI (TP-GFI) systems in the gain-limited orthonormal (GLO) synchronization framework. The proposed theoretical criterion, is universally applicable to arbitrary inverter circuit structures and linear current controls, provides an intuitive stability graphical representation in the complex plane, and allows for frequency-sweeping verification without the use of invasive devices. Finally, the proposed theory is further analyzed, validated and discussed through a conventional case.