A High-Efficiency and Long-Distance Power-Relay System with Equal Power Distribution

This paper proposes a wireless power repeater system for long-distance and multiple-load applications with equal power load at each repeater. Each repeater performs as a power relay that not only receives and transmits power but also supplies power to its local load. The main contribution of this paper is to provide the design methodology of a distributed power-relay system. First, it provides the mathematical model of the power distribution among the power relays, indicating that the inductances and resistances can affect the power distribution. Second, it provides the power transfer capability of a power-relay system based on the quality factor and efficiency requirement, indicating the maximum achievable number of power relays in a system. Aiming at practical applications, this paper provides the guideline for the circuit parameter design to achieve equal power distribution. Two typical examples are proposed to realize equal power distribution. The identical $\text{M}_{\text {n}}$ and different $\text{R}_{\text {n}}$ examples are selected for implementation. The coil size is $400\,\,\text {mm}\times 400$ mm, and the eight power relays achieve a transfer distance of 3.2 m with a total power of 760 W and an efficiency of 70%. Experimental results validate that equal power distribution is achieved for the multiple loads across a long distance. Each power relay dissipates about 95-W power in its local load with a power variation limited to ±2%.