Low-Profile Fractional Planar Transformer Based on a Novel Infinite-shape pcb winding For 5kW Dual Active Bridge Converter

The pursuit of high power density and high-frequency converters has driven advancements in passive components. Planar transformers have emerged as crucial elements in high power density designs due to their low profile and ease of manufacturing. However, in higher voltage applications, ferrite cores with substantial effective core area and higher number of turns are necessary to prevent core saturation. In this paper, a new infinite-shape winding is proposed which employs the side legs of E cores to obtain double effective turns. A planar transformer is proposed using the infinite-shape winding and a ELP 64/10/50 core for a 48V-400V Dual Acitve Bridge (DAB) converter opertaing at 120kHz. By employing a single infinite-shape winding on the 48V side, equivalent to two effective turns, the high-voltage side pcbs can fit into a lower-profile core while maintaining minimal inter-winding capacitance. To meet the demands of this high-power application, parallel infinite-shape pcbs are utilized to increase current capability. A novel interleaving method is proposed to achieve balanced magnetic field exposure and equal current distribution for the parallel windings effectively reducing ac resistance. Finite Element Analysis (FEA) simulations verify the performance of the proposed transformer, demonstrating perfect current distribution and copper utilization. A 5kW DAB converter utilizing the proposed planar transformer is built that achieves 98% efficiency at full power and 3.7 kW/L power density, while the transformer itself reaches 43 kW/L power density with 99.75% efficiency at full load operation.