Optimization of a Two-Layer 3D Coil Structure with Uniform Magnetic Field

Abstract

Conventional magnetically coupled resonant wireless power transfer systems are faced with resonant frequency splitting phenomena and impedance mismatch when a receiving coil is placed at misaligned position. These problems can be avoided by using uniform magnetic field distribution at receiving plane. In this paper, a novel 3D transmitting coil structure with improved uniform magnetic field distribution is proposed based on a developed optimization method. The goal is to maximize the average magnetic field strength and uniform magnetic field section of the receiving plane. Hence, figures of merit (FoM1 and FoM2) are introduced and defined as product of average magnetic field strength and length or surface along which uniform magnetic field is generated, respectively. The validity of the optimization method is verified through laboratory measurements performed on the fabricated coils driven by signal generator at operating frequency of 150 kHz. Depending on the allowed ripple value and predefined coil proportions, the proposed transmitting coil structure gives the uniform magnetic field distribution across 50% to 90% of the receiving plane.

Genetic-Algorithm-Based Optimization of a 3D Transmitting Coil Design with a Homogeneous Magnetic Field Distribution in a WPT System

“…This paper is a continuation of our research on the development of rectangular coil structures that can produce a homogeneous magnetic field intensity distribution. In previous research, the basic structure of a 3D rectangular coil was proposed and results comparable to the state-of-the-art were obtained (the homogeneous area corresponded to 55% of the charging plane) [17]. In this paper, we were interested in further increasing the homogeneous area and the average magnetic field intensity, but also in reducing the coil profile (height).…”

“…The folded TX coil sides originate from the rectangular coil and its magnetic field intensity distribution in the charging plane. Due to the superposition of the magnetic field at the corners of a rectangular coil, the magnetic field intensity distribution in the charging plane over such a coil is nonhomogeneous [17]. Therefore, the shorter sides of the rectangular coil are folded down to eliminate the magnetic field peaks near the corners of the charging plane.…”

“…The width of the first coil layer W was set to 280 mm. This width W has been found to be appropriate for a 3D coil made of two layers [17]. The first coil layer was included in the 2D optimization, but the positions of the squares representing it had a fixed position.…”

“…The 2D model of the flat rectangular coil consisted of only two squares (upper squares in Figure 2). Another 2D model corresponded to the coil optimized in [17], shown in Figure 2. The width of the 2D model of the rectangular coil corresponded to the width of the 2D model of the coil optimized in [17].…”

“…To achieve this, we used the current distribution approach [9] in coil optimization. In the previous study [17], the homogeneous magnetic field intensity distribution was achieved by optimizing the placement of the coil layers. In this paper, with a different current distribution between the coil layers, an additional dimension was added to the optimization process.…”