Effect of DC-Side Dynamics on Interactions in Grid-Forming Inverter Systems

The power modulations carried out by a grid-forming inverter are profoundly affected by the capability of the inverter's dc-side circuit to support such modulations. Although preliminary work on dc microgrids includes the dc-side dynamics, analysis of potential ac-side interactions in the presence of grid-forming inverters is lacking. This paper presents an in-depth study of the interactions in grid-forming inverter systems considering the critical dynamics contributed by the inverter's dc-side circuitry. The study in this paper is based upon dynamic phasor modeling and eigenvalue analysis techniques. The results presented for an exemplar system of a grid-forming inverter paralleled with a synchronous machine prove the significance of including dc-side dynamics to accurately capture the full range of interactions that may occur in such systems. Detailed electromagnetic transient simulation results from PSCAD/EMTDC are included to verify the validity of the predictions of the dynamic-phasor-based model.