Coil Design Method Considering Power, Efficiency, and Magnetic Field Strength of Coreless Coils Using Numerical Analysis in Wireless Power Transfer

Wireless power transfer to electric vehicles while driving is a technology that is currently attracting attention as it has the potential to solve the problems faced by EVs that will become popular worldwide in the future. In the case of dynamic wireless power transfer (DWPT) to electric vehicles, it is necessary to transmit the required power with high efficiency and ensure safety. While there are multiple safety requirements, there are also regulatory values for the magnetic field strength emitted from the coil, which must be satisfied before it can be implemented in society. This research aims to speed up the design of coils by using only numerical analysis, in contrast to conventional coil design using electromagnetic field analysis. In the future construction of wireless power transfer systems, it is of great significance to discuss the design using only numerical analysis, as there are many design parameters. Experiments were carried out and compared with the numerical analysis and found to be in agreement. A power transmission of 20 kW converted value was carried out to verify the effect of the size, pitch, and number of turns of the transmission coils on the efficiency and magnetic field strength. The effect of input voltage was also discussed by simulation, and the optimum coil was derived. As a result, when the coil size was 800 × 600 mm, the number of turns was 46, the pitch was 6.1 mm and the input voltage was 1400 V, the analysis showed that a power transmission of 20 kW with an efficiency of 99.3% and a far magnetic field leakage strength of 81.6 dBμA/m could be achieved. Even with a coreless coil, the magnetic field strength could be below the regulation value.