Improving the transmission efficiency of wireless power trans-fer systems in electric vehicles by using magnetoplated aluminum pipes

Abstract

Wireless power transfer (WPT) technology is becoming increasingly popular because it enables the transmission of electrical energy without the use of connecting wires, which makes the transmission process convenient and safe. Currently, researchers are in the process of developing transmission powers greater than 3 kW for charging electric vehicles (EVs). Some car manufacturers have even started making prototypes using the WPT system. The charging operation tends to be much better in the WPT system because there are no direct electrical connections. The car needs only to be parked at the charging station; subsequently, the WPT system automatically carries out the electrical connection. In the WPT system for EVs, the devices typically use the electromagnetic induction produced between a pair of coils; one coil is for transmitting power, and the other coil is for receiving power. To improve the electromagnetic induction efficiency at high frequencies in the range of 81–90 kHz, a Litz wire of 1000 or more strands is used to reduce the AC loss. The use of a Litz wire reduces the AC impedance resulting from the proximity effect and increases the Q value. Therefore, Litz wires are used in almost all high-power WPT coils [1]. Litz wires can improve performance because they have a greater number of strands than solid wires; they also have low diameters. These attributes, however, also increase the cost of the Litz wire coils. Using a solid wire coil instead of a Litz wire will reduce costs, but the associated high-frequency losses will reduce the efficiency of the coil. Therefore, in this paper, we propose a magnetoplated aluminum pipe (MAP) with a special magnetic layer to improve the transmission efficiency. As compared with the solid wire, the MAP is very light and cheap. Therefore, it is possible to replace the Litz wire with a MAP.