Design of a compact fractional-turn, odd-ratio planar transformer with interleaved windings for distributed energy storage applications

As the application scenarios for distributed energy storage technologies continue to expand, power converters used in these systems must accommodate transformations to various output voltages while also enhancing power density. Planar transformers, with their smaller size compared to traditional transformers, meet the design requirements for increased power density in power converters. In practical applications, a greater variety of planar transformer turn ratios are needed to fulfill an expanding array of application demands. Additionally, it is essential to minimize the parasitic capacitance of the transformer windings in the design. This paper presents a planar transformer with an odd boost turns ratio of 2:3 from primary to secondary windings, achieved through fractional turn design and an interleaved winding configuration that results in reduced parasitic capacitance. The effectiveness of the design is validated through an FEM simulation model, and the winding surface temperature is simulated using CFD. The functionality of the proposed planar transformer is further verified through an LLC resonant converter prototype.