Kw. Klontz et al., AN ACTIVELY COOLED 120-KW COAXIAL WINDING TRANSFORMER FOR FAST CHARGING ELECTRIC VEHICLES, IEEE transactions on industry applications, 31(6), 1995, pp. 1257-1263
A 120-kW coaxial winding transformer has been built and tested to veri
fy previous indications that a high power transformer is feasible with
the key attributes of this novel design, namely: low leakage inductan
ce, minimal effect of leakage field on core losses, low copper losses,
and a convenient ''nesting'' structure well-suited for separability o
f the windings. 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 cha
racteristics, and the results of these design choices as observed in t
he experimental data. The final design has active cooling to facilitat
e high power density and a separable core to allow the primary and sec
ondary windings to be coupled and uncoupled. The experimental data sho
ws performance better than expected, with a magnetizing to leakage ind
uctance ratio of 1000 : 1, efficiency well over 99% and power density
of 25 kW/kg.