Analysis of IPT Intermediate Coupler System for Vehicle Charging Over Large Air Gaps

Intermediate resonant pads have been recently used to increase the ground clearance for inductive power transfer (IPT) systems transferring power over large air gaps. This article investigates the best placement of a tuned intermediate pad to maximize the air gap by assessing the leakage magnetic fields and the apparent power effort. A mathematical analysis is used to design and control a two-coil system with an intermediate pad. The results show that SAE J2954 standard pads can transfer rated power over an extended air gap of 406 mm using an intermediate pad while adhering to the apparent power ratings of all pads and typical leakage constraints. As a comparison, an equivalent IPT system using only a primary and a secondary pad without the intermediate pad is shown to be unable to meet the apparent power and leakage requirements at these large air gaps. Additionally, this article shows and validates control and regulation of the intermediate pad and load current by switching the secondary side.