Planar Fractional-Winding Transformer with Flexible Asymmetric Structure

Planar fractional-winding transformers have the advantages of low winding losses with fractional turns and easy integration, which have shown great potential in improving efficiency and power density in recent years. The current fractional-winding transformers all adopt a completely symmetrical structure, which is too strict for the transformer structure and makes it difficult to use the space flexibly. In addition, it is unclear the impact of structural asymmetry on the operation of the converters. This paper mainly focuses on the structural analysis of the fractional-winding transformer and proposes flexible asymmetric structures. The requirements for the structural design of fractional winding transformers are clarified. The results show that the structural constraints of the transformer can be greatly relaxed, and a flexible asymmetrical structure can also work. The influence of key structural parameters on the circuit is also analyzed. An LLC converter based on a 1/3-turn asymmetric structure transformer was built, which worked well and validated the analysis.