# Development of Wireless Power Transmission System for Transfer Cart with Shortened Track
## 1 Introduction
Especially, in recent years, the electric energy-based wirelessly powered transfer cart (we hereafter call it \"transfer cart\") has been applied to carry an object or a person for a precise manufacturing production in clean environments (including semiconductors or pharmaceuticals) and applications in a small space-constrained workshop [18]. In such a case, a magnetic levitation transfer cart is used to reduce the occurrence of dust. As the magnetic levitation feeder moves without direct contact with the rail without wheels, there is little frictional resistance, which results in very low noise and vibration, and high speed at low power. The power supply of such a transfer cart is generally used in a non-contact manner. That is, the transfer cart includes a power-receiving module provided with a pickup coil, and the power-receiving module is supplied with power in a magnetic induction manner through a high-frequency feed line installed along a moving section of the transfer cart. Therefore, WPT can be considered as an essential technology for various industrial applications [2; 5; 9; 19]. To be an efficient WPT system, improving the energy conversion efficiency and increasing the power transfer distance of WPT are essential [3; 5; 6; 8; 9; 11; 13; 15; 16; 18; 20]. In particular, for a variety of applications in the industry where a clean environment is required or when there is limited space in the workplace, it is necessary to be able to design a pickup module with a shortened track. Generally, the typical track length is long, and a trap box is installed in the middle of 100 to 200 m to meet the LC resonance. In this study, we designed and fabricated a pickup module for application to a shortened track with a length of 6 to 10 m, and its performance was confirmed by performing experiments. In [21], they provide electromagnetic field analysis to improve the core performance and coil design for maximizing efficiency, and in [22], they propose some techniques for the reduction in electromagnetic fields (EMFs) from the power line and vehicle. In our design of the pickup unit including a regulator (secondary side) and a track (primary side) made of Litz wire (see Figure 1a,b), MRM-based design methods were originally developed for applications to wireless charging systems for electric vehicles of [21; 22]. A previous conference paper has briefly introduced the potential of this strategy [23]. To improve the performance of the WPT system and to develop the module for a shortened track, the tasks we conducted in this work are:  
1. Design to maximize efficiency considering several key design parameters of the coil,
2. Coil design considering high efficiency, electromagnetic interface (EMI), electromagnetic field (EMF), and form factor,
3. The selection of an appropriate frequency for maximum efficiency, minimum material loss, and minimum EMF,
4. An active shielding method using a resonant loop current shielding (RLCS) canceller,
5. Structural designs to improve the heat transfer performance of a module,
6. Module fabrication for performance verification. To increase the efficiency of power transmission by increasing the reactance, the Litz cable is lengthened from 100 to 200 m in an industrial site. When the Litz cable is long, the line in the factory is complicated, resulting in limited space usage. Therefore, the Litz cable needs to be shortened. For this purpose, a module with a core structural shape was fabricated and applied in our study. This paper presents the power transfer system design in Section 2. Section 3 describes the thermal analysis and pickup module fabrication. Section 4 offers test methods and results. Lastly, Section 5 concludes the paper.