Mutual Inductance Analysis of Rectangular Spiral Coils with Angle and Position Variations for Wireless Power Transfer

Abstract

For wireless charging, a misalignment between a receiver (Rx) coil in the devices (EV, drone and IMD) and a transmitter (Tx) coil often occurs. In this case, a mutual inductance between the coils changes, and consequently a power transfer efficiency (PTE) of the wireless power transfer (WPT) system also changes. To analyze the WPT system in such a situation, this paper presents an analytical method using Neumann formula to derive mutual inductance considering angular and position variations of two rectangular spiral coils. To verify the proposed method, magnetic resonant WPT systems of 85 kHz and 6.78 MHz are implemented, and the PTE values derived from the analyzed mutual inductance and the measured S-parameters are compared for the cases of angle and position variations. For each case, the two PTE values agree well with each other, and it is verified using the normalized root mean square error (NRMSE) values.