Three in One Coupled Inductor for High-Power-Density Capacitively Isolated DC/DC Transformer

This paper proposes the novel three-in-one coupled inductor for the capacitively isolated DCX (DC/DC Transformer) for low-voltage DC supply systems. The capacitive isolation topology is one of innovative solutions to overcome the trade-off between the efficiency and the power density of DCXs such as unregulated LLC resonant converters. However, in the capacitively isolated DCX, the volume of inductors for the LLC resonant circuit is still dominant and poses a barrier to achieve higher efficiency and power density. The proposed three-in-one coupled inductor enables to achieve both low-loss and compact inductor by integrating two series resonant inductors and one parallel inductor in the conventional capacitively isolated DCX. The virtual design for the proposed coupled inductor has been carried out for a 48 V-48 V, 450 W capacitively isolated DCX, and it is shown that the designed coupled inductor has the potential to reduce 23% in volume and 15% in loss compared with conventional three inductors. A first prototype of the coupled inductor has been developed to confirm the validity of the proposed three-in-one integrating topology. The demonstration of the DCX utilizing the coupled inductor has verified the validity. The proposed coupled inductor contributes to improving the efficiency and the power density of the capacitively isolated DCX.