Study of the Circular Flat Spiral Coil Structure Effect on Wireless Power Transfer System Performance

Xu Liu,Xibo Yuan,Chenyang Xia

doi:10.3390/en11112875

Abstract

This paper analyses the relationship between the coil design parameters and the system performance, including power transfer efficiency and amount, when circular flat spiral coils are adopted in a wireless power transfer (WPT) system. Coil design variables including outer radius, inner radius, channel width and coil turns are thoroughly studied to improve the system performance with a limited maximum outer radius for practical purposes. A two-coil WPT system has been built to verify the analysis, and the experimental results show good consistency with the theoretical calculations and simulation results, which show that the coil design parameters have a significant impact on the system performance, even with the same coil size. In the experiments, the coil-to-coil distance is 150 mm, the maximum coil outer radius is limited in 300 mm, and the DC input voltage and the load resistance are 100 V and 5 Ω, respectively. When the coils are tightly-wound in the most traditional way to maximize the coil size, the coil-system efficiency is 62.6% with only 4.5 W load power. In contrast, the efficiency optimized coil can improve the coil-system efficiency to 91.2% with the outer radius stayed the same. Besides, when the power transfer efficiency and amount are considered simultaneously, the system can achieve 1279 W load power with 85.94% coil-system efficiency.

Highlights

wireless power transfer (WPT) systems utilize the magnetic field to transfer energy from a power source to isolated loads across a large air gap without direct electrical contacts which can be used for powering up any electric equipment
These two coils are separated with an air gap and tuned to resonate by the compensation circuit at the same natural frequency which is known as resonant wireless power transfer (RWPT)
In order to find out which method is the best choice for achieving a better system performance and which one is more suitable for a certain requirement, a comparison is made firstly among the first three methods as introduced in Sections 3.1–3.3, as these three tuning methods to limit the maximum outer radius of the circular flat spiral coil in a certain value can all be presented by coil-turns changing, the system performance can be made a fair comparison for these three methods

Summary

Introduction

WPT systems utilize the magnetic field to transfer energy from a power source to isolated loads across a large air gap without direct electrical contacts which can be used for powering up any electric equipment. A WPT system is at least composed of two coils which are known as transmit and receive coils and can be named a two-coil WPT system [1,2,3] These two coils are separated with an air gap and tuned to resonate by the compensation circuit at the same natural frequency which is known as resonant wireless power transfer (RWPT). As the energy is wirelessly transferred through the mutual inductance between the transmit and receive coils, the leakage inductance does not have a direct contribution to the active power transfer, and the large gap between the transmit and receive coils will lead to a very small coupling coefficient between the two coils.

Methods

Findings

Discussion

Conclusion