Robust Ferrite-Less Double D Topology for Roadway IPT Applications

Roadway inductive power transfer depends on robust and reliable primary magnetic couplers (pads), but existing pads use large quantities of ferrite, a brittle magnetic material. This paper presents a ferrite-less variation on the Double D topology, removing the ferrite thereby making the system more mechanically robust, and then adding an additional reflection winding to help shape the field. A relevant background to IPT systems is presented, followed by a mathematical analysis of the impact of the added reflection winding. The effect of the number of turns, the depth and the area of the reflection winding is presented, with simulations, pad dimensions, and laboratory validations. The proposed ferrite-less DD variation has a lighter weight and a similar cost, but requires a higher primary pad current to deliver the same power. It has a lower leakage where humans may be present at the side of the vehicle and a higher leakage magnetic field into the road substrate compared to a pad with ferrite. The final proposed system is capable of delivering 7.7 kW fully displaced at an air gap of 175 mm with the worst case leakage within the ICNIRP leakage limits and is validated at both 3.3 and 5.7 kW using equipment readily available in the laboratory.