Dual-Band Free-Positioning Transmitting Coil for Multiple-Receiver Wireless Power Transfer

Abstract

In recent years, the requirement for a compact wireless power transfer (WPT) system that can supply power to multiple devices in various practical usage scenarios has been attracted many researchers. The receiver (Rx) misalignment problem is contributory to the power transfer efficiency (PTE) degradation. Moreover, in a multiple-output WPT system, the overall system efficiency is also affected by cross-coupling between receivers. This paper proposes a dual-band free-positioning transmitting coil (FPDB-Tx) for multiple-receiver WPT. A three-dimensional Tx structure is modeled by investigating the current direction on each coil loop to adapt the Rx angular and axial misalignment. The Tx configuration is designed following a wireless charging box concept, where multiple Rx devices can receive energy freely without a null efficiency point. The mutual inductance is examined by a mathematical method in various Rx orientations to verify the free-positioning characteristic. Furthermore, an equivalent circuit model of the WPT system is theoretically analyzed to obtain dual operating frequency bands and then maximized the PTE. The experimental results show that the proposed WPT system achieves a stable PTE in various Rx positions. Especially, the WPT system has a maximum PTE of 97.27% and 91% at 6.78 MHz and 13.56MHz, respectively.INDEX TERMS wireless power transfer, free-positioning WPT, multiple-receiver WPT, dual-band WPT, mutual coupling, impedance matching network.

A parabolic spiral coil transmitter with uniform magnetic field for smart devices

“…Regarding single input multiple output (SIMO) technology that can charge multiple devices at the same time, the following methods have been presented: a multifrequency WPT system that switches between multiple frequencies for receivers with different resonances [10,11,12]; a multi-receiver system that has a relay coil and capacitive compensation for each receiver to eliminate the effects of frequency splitting and cross coupling by means of independent resonance frequencies [13]; stabilization control of secondary voltage by a DC-DC converter [14]; time division control [15,16]; and a maximum efficiency tracking method with a fixed power division ratio using perturbation and observation (P&O) algorithm control methods [17]. However, additional equipment for control requires space and makes the system complicated.…”

Anti-Symmetric Wing Transmitter for Angular Misalignment Insensitive Wireless Power Transfer to Biomedical Implants

“…In near-field magnetic resonance coupling WPT (MRC-WPT), the double-D (DD) coil structure has been suggested to avoid efficiency degradation by rotating Rx [3]- [5]. However, it requires a bipolar Rx, which has the same field characteristic as the Tx coil to receive power well in the center of a DD-Tx [4].…”