Loosely Coupled Transformer Structure and Interoperability Study for EV Wireless Charging Systems

Abstract

As the wireless power transfer (WPT) technology has been proved to be a convenient and reliable charging method to plug-in hybrid electric vehicles (PHEV) and electric vehicles (EV), the loosely coupled transformer structure and size are the primary and fundamental concern to design an efficient WPT system. In this paper, a double D (DD) coil and a unipolar coil are selected to conduct the study. We focus on the coil structure design to achieve the maximum coupling coefficient as well as efficiency with two situations: (a) with no misalignment, and (b) with a 75mm doorto-door, and 100mm front-to-back misalignment at which the maximum operating capability (MOC) can still be achieved. A coil size optimization process is proposed for both the DD coil and the unipolar coil configurations. The relationship between the size of the secondary (receiving) coil, which determines the weight of the pad on the vehicle, and achievable maximum efficiency is studied for both coil topologies. The interoperability between the two coil topologies is studied. The proposed transformer structures with aluminum shielding meet human exposure regulations of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines as a foundation. Finally experiments validated the analyses.Index Terms-Wireless power transfer, electric vehicle, loosely coupled transformer, interoperability, safety, electromagnetic radiation. 0885-8993 (c)

Coil Design for High Misalignment Tolerant Inductive Power Transfer System for EV Charging

“…At 100% misalignment offset, the efficiency of the IPT system drops drastically. With proposed coil design, the misalignment tolerance is extended to 50% of the coil size and can be considered as a significant improvement [33,34]. There has been work on different designs of coils for the IPT system in which magnetic coupling is sensitive to the position of coils with respect to each other [35,36].…”

Scaling Rules at Constant Frequency for Resonant Inductive Power Transfer Systems for Electric Vehicles

“…The magnetic field distribution is influenced by the presence of the vehicle chassis that usually exhibits a predominant conductive behaviour [30,31]. Moreover, aluminium shields are often used to confine the magnetic field for electromagnetic compatibility reasons while magnetic materials can be used to guide the magnetic flux, increasing the coupling and improving the tolerance to transmitter-receiver misalignments [13,14,32].…”

“…Unlike the standard transformer, the coupling takes place through a large air-gap on the order of some tens of centimeters. Hence, the flux is not constrained to a well defined path and the coupling between the two sides is typically lower than 30% [12][13][14]. Ferrite bars are added to the coils in order to compensate for this coupling reduction.…”

Optimization of structure and control strategy for EV wireless charging systems

“…Zhao et al [5] developed a method called phase-shift control to alleviate change of efficiency when input power changes. Zeng et al [6] and Zhang et al [7] optimized the magnetic core structures by FEM simulation and experiments, reducing the weight of the magnetic couplers as well as improving the efficiency, and Zeng et al [6] proposed a method of optimizing the core structure. The copper losses are analysed in [8] in order to reduce the losses in the coupler.…”