Equalization Method of the Wireless Power Transfer in an Electronic Shelf Label Power Supply System

In a wireless power transmission device that drives multiple power outputs for electronic shelf labels (ESLs), we propose a novel rail transformer design for use with a 50/60 Hz power supply. By periodically short circuiting the receiving coils located closest to the transmitting coil, we experimentally verified that power can be transmitted to each ESL in a significantly uniform fashion. We expect the present approach with periodically switched receiver coils to be much more convenient, reliable, and flexible than our previous method of physically adjusting the air gaps between coils. In verification experiments, the output power of three receiving coils in a prototype was equalized at a level of approximately 60 mW. Without periodic switching, the output power of the center receiving coil only reached 40 mW, whereas, the receiving coils closest to the transmitting coils reached an output level of 80 mW, with output power fluctuating by approximately 49%. This paper demonstrates an effective design strategy for wireless power transfer devices.