An actively cooled 120 kW coaxial winding transformer for fast charging electric vehicles

A 120 kW coaxial winding transformer has been built and tested to verify previous indications that a high power transformer is feasible with the key attributes of this novel design, namely: low leakage inductance, minimal effect of leakage field on core losses, low copper losses, and a convenient "nesting" structure well suited for separability of the findings. The power transfer capability is more than double that of any previously published result for coaxial winding transformers. The application chosen for the fabricated transformer was an inductive coupler for fast charging of electric vehicles. Presented are the key parametric decisions, their impact on transformer fabrication and characteristics, and the results of these design choices as observed in the experimental data. The final design has active cooling to facilitate high power density and a separable core to allow the primary and secondary windings to be coupled and uncoupled. The experimental data shows performance better than expected, with a magnetizing to leakage inductance ratio of 1000:1, efficiency well over 99% and power density of 25 kW/kg.