Resonance analysis in parallel voltage-controlled Distributed Generation inverters

Thanks to the fast responses of the inner voltage and current control loops, the dynamic behaviors of parallel voltage-controlled Distributed Generation (DG) inverters not only relies on the stability of load sharing among them, but subjects to the interactions between the voltage control loops of the inverters and the remaining system dynamics. This paper addresses the later interactions and the consequent resonances through the frequency-domain analysis of the inverters output impedances and the remaining equivalent network impedance. Furthermore, impacts of the virtual output impedance loop and the voltage feedforward loop in the current controller are evaluated based on such an impedance interactions analysis. Simulation results are presented to confirm the validity of the theoretical analysis.