An Improved Calculation for Ohmic Resistance of Round-wire Self-Resonant Coils in High-Frequency Wireless Power Transfer System

This paper presents an improved method for calculating the ohmic resistance of round-wire self-resonant coils in high-frequency wireless power transfer (WPT) system. At the self-resonant frequency, the current distribution is not identical along the coil. To address this, we employ the filament method and establish a segmented filament model to determine the self-resonant frequency and current distribution. Additionally, given the uneven current density distribution across the wire’s cross-section, a modified segmented filament model is proposed. This modified model decomposes the current into a skin current filament and a pair of proximity current dipoles. The magnetic field induced by neighboring wires is subsequently computed, enabling the determination of proximity resistance. Simulation and measurement results validate the precision of the modified model for coils wound either tightly or loosely. The proposed model is further applied in optimizing the ohmic resistance of self-resonant coils. Subsequently, an experimental prototype of high-frequency WPT system is built employing the optimized self-resonant coils. Specifically, the system efficiency attains 72.89% with a 200Ω load at a transfer distance of 20cm.