Reduced Ferrite Double D Pad for Roadway IPT Applications

Roadway inductive power transfer presents an opportunity to provide a robust and user friendly system for electric vehicle charging by utilizing magnetic couplers (pads) embedded in the roadway. Roadway pads are expected to have a long service life but existing pads use a large quantity of the brittle magnetic material ferrite, which may break in the harsh environment of a roadway. This article shows what happens when the volume of ferrite material is reduced from an example double D pad to minimize the quantity and size of ferrite that needs to be protected. Also presented are design insights into the placement of a reflection winding that helps shape the field in the absence of the majority of ferrite. The final selected example design reduces the leakage magnetic field where a person may be present by 43%, at the expense of an increase in primary VA of 73% from the original double D pad. The final presented pad reduces the ferrite volume by 86% compared to the original example double D pad, is only 50 mm thick, and is shown to have a measured dc-dc efficiency of 91% when delivering 4.7 kW to an available secondary.