Analysis of efficiency stability for relay based wireless power transfer system

Abstract

Wireless power transfer system based on magnetic resonance is transmitting power by using magnetic field, like magnetic induction, and its power transfer distance is longer than wireless power transfer based on magnetic induction. Most important factors in wireless power transfer are the power transfer efficiency, distance and stability. Wireless power transfer systems have a trade-off relationship between power transfer efficiency and distance so we should design the system to serve its purpose whether the wireless power transfer system should provide the higher power transfer efficiency or larger power transfer distance. However, there is a lack of research of stability of wireless power transfer system based on magnetic resonant technique. Although magnetic resonant technique provides the high power transfer efficiency over several meters, it has a critical problem that the power transfer efficiency of 2 coils wireless power transfer system is very sensitive to location or orientation of coil antennas. Therefore, magnetic resonant based wireless power transfer system can not be commercialized, although magnetic resonance technology has taken a spotlight recently. Therefore, we should address the critical problem that the wireless power transfer system is unstable. To address the stability problem, we analyzed the 2 coils wireless power transfer system to verify why this system is unstable according to coupling coefficient. The traditional 2 coil wireless power transfer system has a optimal coupling coefficient. The transmitter coil and receiver coil are coupled with as much as optimal coupling coefficient, and this system provides highest power transfer efficiency. Therefore, power transfer efficiency was varied significantly because of coupling coefficient variation that is induced from locations or orientations of coils. The 3 coils relay based wireless power transfer system is a solution of stability problem of traditional wireless power transfer system....