Design and Efficiency Optimization of Asymmetric Magnetic Coupled Resonant Wireless Power Transfer System

The two-coil magnetic coupling resonant wireless power transfer (MCR-WPT) system has the disadvantages of short transmission distance, and low transmission efficiency when distance between the two coils is long. In this paper, the relay coil is added to improve the transmission distance and transmission efficiency of the system. The reflection impedance circuit model is established by circuit theory, and the expression of transmission efficiency is derived. In this article, the asymmetric structure of system is studied, and a rectangular coil is proposed. Then the coil and ferrite parameters are optimized and analyzed. The performance of the proposed rectangular coil system is compared with that of the traditional circular coil system. It is found that the efficiency of circular-rectangular-circular (transmitting-relaying-receiving) three coil system, rectangular-rectangular-rectangular three coil system and the traditional circular-circular-circular three coil system all reach more than 89%. Among the above three asymmetric coil systems, the efficiency of the previous two systems is 0.07% and 2.51% higher than that of the three-circular coil system, respectively. It is concluded that the rectangular coil can improve the system efficiency compared with the circular coil. With ferrite, the transmission efficiency of the three coil systems is increased by at least 3.41%, and the maximum efficiency of rectangular-rectangular-rectangular three coil system can reach 95.78%.