Analysis of interactions among parallel grid-forming inverters.

Parallel operation of grid-forming inverters (GFMIs) is often achieved using droop characteristics implemented in converter controllers. Converters' recovery after a disturbance depends on the dynamics of each individual GFMI, and the droop characteristic alone is unable to ensure successful parallel operation. This work proposes a dynamic-phasor based modeling approach that enables eigenvalue analysis of multi-converter systems to identify the underlying factors that affect the interactions among parallel GFMIs. Network dynamics are included through dynamic phasor modeling of its elements, and controller dynamics are fully included. Modeling modularity is preserved, which allows to easily extend the test system to any topology of interest. The results presented for an exemplar two-converter system prove that the virtual inertia time-constant plays a significant role in exciting interactions, and that network and control system parameters are vital in extending the stability margins of the systems. EMT simulation results from PSCAD/EMTDC are included to verify the validity of the predictions of the dynamic-phasor based model. • A modeling platform based upon dynamic phasors is developed form small-signal modeling of multi-converter systems. • Using the developed platform interactions among grid-forming converters in low-inertia systems is studied. • Several factors contributing to interactions among grid-forming converters are identified. [ABSTRACT FROM AUTHOR]