Design and optimization of a multi-coil system for inductive charging with small air gap

This paper focuses on the magnetic design of a multi-coil system for an inductive power transfer (IPT) system for charging electric vehicles with a small air gap between transmitter and receiver coils. Thus, external stray fields can be reduced and the expense of material decreases compared to systems using a large air gap. The magnetic design of the multi-coil system is optimized for the given package space of the vehicle by using a new coupled numeric approach and considering additional coil geometries as well as alternative winding structures. The result of this design process presents the basis to build up a prototype system, including an additional secondary side DC/DC converter. Therewith, an efficiency between 92% and 96% at an output power of up to 3.5kW is achieved.