Air-gap insensitive and small form-factor IPT pad design for electric vehicles

Abstract

In this study, we propose a inductive power transfer (IPT) technology that can be applied to various transportation systems such as electric vehicles (EVs) and automated guided vehicles (AGVs) using the characteristics of ferrite core and aluminum. First, a new conductive-plate-integrated IPT system for AGVs with little output power variation according to air-gap changes between the transmitter (Tx) and receiver (Rx) is proposed. The inductance change of the ferrite core due to variations in the air-gap is nullified by a corresponding change in an aluminum plate. Compared to conventional ferrite IPT systems, self-inductance of the proposed Tx coil is little changed against air-gap variations, which results in robust resonant frequency and output voltage. The self-inductance was experimentally verified to remain within 0.45% even when the air-gap changes by fivefold from 10 mm to 50 mm. The output power variation became a twelfth of that of the conventional ferrite IPT for air-gap variations of 30 ~ 50 mm, where the efficiency was found to be 96.0% when the output power was 1 kW. Second, a new toroidal-type compensation coil structure for integrated-LCC topology is proposed. By integrating the toroidal-type compensation coil to main coil, unwanted cross coupling is fundamentally eliminated. The proposed structure is verified through experiments that the compensating inductor can be integrated to the Tx and Rx without additional magnetic material. Experimental results show that the proposed structure has the same performance compared with the conventional LCC circuit with an external inductor when the output power was a 3.3 kW.