Investigations on an inductive power transfer coupler with two or three windings
Rapport, 2015

In this paper the use of two or three resonant coils in the transformer part of a high power transfer system is analysed. The inductances for actual coil setups are calculated using FEM programs. Kirchhoff's laws are then used for calculation of currents, voltages and power. Approximate equivalent circuits of the transformer as seen from the sending and receiving coils are developed. The voltage fed to the transformer is a square wave. It is possible to use only the fundamental frequency component for the calculations. A laboratory device is used for measuring and calculation of losses, the magnetic fields etc. This charger is carefully examined. It is found that two or three coils can transfer the desired power to the load. The auxiliary coil must be close to the sending coil. The frequency must be close to resonance. It is also found that the 2 or 3 coils setups will have almost the same efficiency. Using three coils it is easier to lessen the magnetic field inside and outside the charger. The three coil model is less sensitive to misalignments.

electric vehicle

third winding


inductive charging

high power transfer


Eva Palmberg

Chalmers, Rymd- och geovetenskap




Grundläggande vetenskaper


Annan elektroteknik och elektronik

Technical report - Department of Energy and Environment, Division of Electric Power Engineering, Chalmers University of Technology

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