High Current, Low voltage IPT application

Abstract

Inductive Power Transfer (IPT) technology is a process which allows power to be transferred between two loosely coupled magnetic pads by using the principles of electromagnetism. The primary magnetic pad produces an alternating magnetic field which is picked up by the secondary pad and is regulated to meet the demands of the load. This technology has found use in a range of applications which include material handling applications, charging of electric vehicles, clean factory industries. In this thesis, the focus will be to wirelessly charge an Automated Guided Vehicle (AGV) application with high current and low voltage output demand. Due to increasing power density demand by a commercial client, it was causing heating issues in the primary magnetic pad. Therefore, a magnetic analysis was carried out which was followed by the investigation of various novel passive cooling techniques. The improved primary magnetic pad involved introducing a gap between the different ferrite blocks. An aluminium block was placed in-between the gap which allowed contact between the Litz wires and the aluminium back plate. The remaining air gaps within the pad was filled with thermal grease and the thickness of the aluminium was increased by a couple of millimetres. This combination of changes showed a marked decrease in temperature from 85.7oC to 51.3oC, which met the client's thermal requirement. To charge an AGV with high current and low voltage, an interleaved buck converter and a current doubler were investigated. However, these were too bulky and had an increased component. Therefore, a recently developed "Current Multiplier" (CM) topology for high current applications was investigated. In this topology high current only flowed in the output winding of the CM while other windings had lower currents therefore reducing the copper losses and device losses. A mathematical model of the IPT based CM system (IPT-CM) was developed which provided equations for the current, voltage, impedance and reflected impedance of the system. This was followed by a MATLAB analysis which showed the effects of changing the different parameters of the system. A final system was recommended, and an experiment was done on a 1kW load. Since, batteries need to have current and voltage regulated therefore different control schemes were analysed. The final controller implements a primary side controller for regulating power flow to the battery with a AC controller at the secondary to act as a fail-safe mechanism.