Impedance model based coordination control of secondary ripple in DC microgrid

Abstract

The connection of single-phase AC loads to a DC microgrid not only large secondary currents flowing into energy storage units with droop control cause, but also lead to secondary voltage ripples appeared on the DC bus, which seriously affects the normal operation of DC microgrids. In this paper, the secondary currents and voltages can be suppressed simultaneously by means of reconstructing the output impedances of energy storage converter and active capacitor converter. The main characteristics, impedance model, control strategies, and system stability in terms of secondary ripples are comprehensively investigated. Particularly, it is shown that the output impedance of the energy storage converter with droop control is relatively small and the input impedance DC loads buck converter are relatively large, so the secondary currents mainly flow into energy storage units and DC bus capacitor. Based on this, the output impedance of the energy storage converter and active capacitor converter are reconstructed relatively larger and smaller respectively, so the secondary currents mainly flowing into the active capacitor. Therefore, the secondary ripple currents flowing into energy storage units and the secondary ripple voltages appeared on the DC bus can be suppressed. Finally, the proposed methods are varied through simulations results.