Resistance optimization of a coil with substrate and design of a high-power-density coupler for wireless power transfer

Abstract

Wireless power transfer (WPT) technology has been popularized due to its convenience, safety, and unmanned nature. To improve the transmission performance of couplers and reduce the magnetic field, the designers of such couplers often adopt a combination of coils and substrates: however, the non-ferromagnetic substrate often leads to the enhancement of coil equivalent resistance and the decrease of the efficiency of a WPT system. In the present work, the effect of a substrate on coil equivalent resistance is evaluated by finite element simulation. The effects of the distance between a substrate and a coil and the number of turns of coil on the equivalent resistance of coils are studied. Based on the calculation method of alternating current resistance for Litz-wire, the equivalent resistance reduction method involving use of a coil with substrates is proposed to significantly reduce equivalent resistance of the coil with its substrate. A high-power-density coupler is designed based on the above method. The power densities of a transmitting coil and a receiving coil are only 0.542 W/cm ³ and 0.81 W/cm ³ respectively. When the transmission distance is 200 mm, a power transmission of 3.61 kW is realized, and the efficiency of the coupler and system reaches 94.61% and 92.56%, respectively.

Keywords: Coil resistance; Coupler; Substrate; Transmission performance; Wireless power transfer.