Interleaved PCB Winding Planar Transformer for Electric Vehicle Charging CLLC Converters

As the growth in electric vehicle (EV) chargers continues to push research towards compact and efficient power converters, high-frequency magnetic designs become pivotal. However, they introduce new challenges related to excessive magnetic losses and adverse parasitic components. Using planar transformers with PCB windings can address these by offering good heat dissipation, low losses, and controlled parasitics. Furthermore, interleaved winding configurations can circumvent traditional design trade-offs. Therefore, this paper presents a planar transformer design using PCB windings with novel interleaving and design aspects to minimise the losses and parasitic components of the high-frequency transformer. It aims to achieve an optimal balance between the trade-offs whilst ensuring compatibility with the target converter’s requirements and cooling system. The proposed anti-symmetrical interleaving achieves a drastic reduction of factor 8.6 in interwinding capacitance compared to conventional full-interleaving combined with low winding losses. The paper provides extensive comparison studies of different interleaving types, supported by thorough finite element simulations. The resulting design approach is applied to a 4 kW isolated dc-dc converter for level-1 EV charging. Finally, different prototypes are built and extensively characterised and validated for implementation in the EV charger. The resulting transformer features a gravimetric and volumetric power density of 15.1 kW/kg and 76.4 kW/l, respectively.