Improvement of Light Load Efficiency for Buck-Boost DC-DC converter with ZVS using Switched Auxiliary Inductors

This paper proposes a changing buck-boost inductance for non-isolated bidirectional buck-boost DC-DC converter with zero voltage switching (ZVS) modulation in order to achieve high efficiency at wide load region and a wide voltage variation. In the proposed converter, the auxiliary inductor and the bidirectional switch are connected in parallel to a main inductor, and each connection is switched depending on the load condition. At the light load region, the bi-directional switch is turned off for the reduction of the converter loss with the large equivalent inductance. On the other hands, the auxiliary circuit is utilized at the heavy load region in order to extend the power translation range with the small equivalent inductance. In addition, the sequence for the switching auxiliary inductor is also proposed in order to prevent the surge voltage of the bidirectional switch and the DC offset current in the auxiliary inductor. From the experimental results, the root mean square value of the inductor current is reduced by up to 23.8% compared with that of the conventional converter. In addition, the validity of the proposed sequence is also confirmed, e.g. no surge voltage at the turn off of the auxiliary inductor. Moreover, 41% of the converter loss reduction at the light load region.