Reduced-Order Model for Inter-Inverter Oscillations in Islanded Droop-Controlled Microgrids

Representing a major technology toward the proliferation of sustainable energy resources, droop controlled microgrids have attracted numerous modeling approaches with a view to improving their operation and applicability. Acknowledging the low inertia of distributed generators and the network characteristics at the distribution level, this paper proposes a reduced order model for inter-inverter oscillations in autonomous droop controlled microgrids. At first, a simplified equivalent network on the basis of Kron reduction is suggested as an effective topology for the study of inter-inverter oscillating currents. The focus shifts toward low-frequency modes following the detailed small signal model and its simplification according to the singular perturbation theory with multiple time scales. Assuming accurate and instantaneous tracking of the voltage by the inner controllers on their local reference frame, the quasi steady state study results in a simple closed-loop model. This model is successfully benchmarked against the detailed model and other germane models over the full range of operational damping ratios.