Study On Some Key Technologies Of Wireless Power Transfer Based On Coupled Magnetic Resonances

Wireless power transfer (WPT) based on strongly coupled magnetic resonances has been attracting a great deal of attention in applications such as wireless power charging system, implanted biomedical devices, consumer electronics, passive sensors, portable lighting, electric vehicles and radio-frequency identification (RFID). Unlike the traditional inductively coupled power-transfer systems, strongly coupled magnetic resonance systems can transfer electric power over a fairly large distance (i.e., more than twice the coil diameter) with a higher efficiency (i.e., up to 80%).The present study of wireless power transfer system with one source and one receiving device has attracted wide attention both in theory and engineering practice, and WPT system with one source and multiple receiving devices which is closer to practical applications has become the urgent subject need to be studied; besides, the introduction of relay resonator provides a high efficient solution for long-distance wireless energy transmission. Therefore, this paper has done some research around WPT system with multiple receiving device, new structure of relay resonator and other hot issues. The purpose of this paper is to promote the conversion of wireless energy transfer technology to practical applications.First of all, the structure of the wireless energy transfer system with one source one device (four coil structure) is introduced. The working principle, energy transfer process as well as the procedure to be followed in the system is concisely presented. Then, the mathematical model has been established for wireless energy transfer system using the coupled-mode theory and circuit theory respectively, and the equivalence of the two theories for design and optimization of the system is demonstrated. In the end, a detailed analysis of the principle parameters based on circuit theory for the WPT system based on coupled magnetic resonances is presented, and the optimizing process for the WPT system of four coil structure is analytically derived from the theoretical point of view.Secondly, circuit analysis of the wireless power transfer (WPT) system with one source and multiple receiving devices is presented. The equivalent circuit model of the original four coil WPT system is expanded for this multiple devices WPT system. The maximum power transfer efficiency and impedance matching for source resistance is discussed. The tuning scheme for optimizing the WPT system is derived analytically. The circuit analysis and tuning scheme of the WPT system is validated by the experimental results and circuit simulations. The proposed circuit modeling scheme provides an efficient way for designing and optimizing the multiple-device WPT systems.Thirdly, a novel WPT system with double intermediate resonators is proposed. In addition to the power and load coils, this WPT system has four self-resonators:a sending resonator, a receiving resonator, and two intermediate resonators. For optimal design, this WPT system is analyzed using an equivalent circuit model. In particular, a tuning scheme for coupling coefficients is proposed to determine optimal positions of the power and load self-resonators for maximizing the power transfer efficiency. The experiments show that the electric power can be wirelessly transferred to the receiving coil located at a distance more than four times the resonator diameter away from the sending coil with high efficiency.Fourthly, a cascade structure of double intermediate resonators system is proposed, the structure is consist of multi intermediate resonators perpendicular to the sending coil which can be applied to wireless energy transfer in large indoor space. A preliminary study of the basic features has been done by simulations, and the effect of the resonant coil resistance on the transfer efficiency is analyzed. The factors which affect the transfer efficiency of the cascade system is analyzed, such as the ac resistance of the resonators, position of the resonators and the resonant frequency. The tuning scheme is summarized through the research and analysis to enhance the performance of the cascade system.Finally, the previous work is summarized and extended, which points out the shortage of work and the development direction of this study in the future.