An AC/DC bus voltage quality coordinated control strategy in hybrid microgrids

Abstract

In hybrid AC-DC microgrids, the unbalanced voltages at the point of common coupling (PCC) cause instantaneous power fluctuations in the interlinking converters (ILCs). It will generate second-order ripple on the DC bus. Meanwhile, the integration of single-phase AC loads into the DC bus also injects second-order ripple to the DC bus, aggravating the imbalance problem at the PCC. These two issues are coupled to each other, leading to severe power quality problems. Additional equipment, such as active power filter (APF), will increase costs and cause instability. This paper proposes a coordinated control for ILC and bidirectional dc–dc converters (BDCs), which connect supercapacitor to the dc bus. The control parameters are determined according to the redundant capacity of the power converter to achieve a reasonable oscillating power sharing between the ILC and the BDC. An indicator considering both voltage imbalance at the PCC and second-order ripple is used to attain optimal coordinated control parameters. The proposed control strategy suppresses the second-order ripple in the DC bus while improving the voltage imbalance at the PCC without any additional equipment. Its effectiveness is verified through simulation results.