Magnetic coupling resonance wireless power transfer (MCR-WPT) technology has been in development for over a decade. The output power of the MCR-WPT system achieves the maximum value at two splitting frequencies and not at the natural resonant frequency because frequency splitting occurs in the over-coupled region. In order to achieve excellent transfer characteristics, optimization approaches have been used in many MCR-WPT projects. However, it remains a challenge to obtain a constant output power in a fixed-frequency mode. In this research, two receiving coils are used in the MCR-WPT system to achieve a uniform magnetic field. First, a circuit model of the MCR-WPT system is established, and transfer characteristics of the system are investigated by applying the circuit theory. Second, the use of two receiving coils to achieve a uniform magnetic field is investigated. Constant output power is then achieved in a fixed-frequency mode. Lastly, the experimental circuit of the MCR-WPT system is designed. The experimental results are consistent with the theoretical ones. The topology of using two receiving coils results in optimum transmission performance. Constant output power and high transfer efficiency are achieved in the higher frequency mode. If the distance between the two receiving coils is appropriate and the transmitting coil moves between the two receiving coils, the fluctuation of the output power of the MCR-WPT system is less than 10%.
2. Wireless power transfer, , https://en.wikipedia.org/wiki/Wireless_power_transfer.
3. Kurs, A., et al., "Wireless power transfer via strongly coupled magnetic resonances," Science, Vol. 317, No. 5834, 83, 2007.
4. Erfani, R., et al., "Modeling and characterization of capacitive elements with tissue as dielectric material for wireless powering of neural implants," IEEE Transactions on Neural Systems and Rehabilitation Engineering, Vol. 26, No. 5, 1093, 2018.
5. Mcspadden, J. O. and J. C. Mankins, "Space solar power programs and microwave wireless power transmission technology," IEEE Microwave Magazine, Vol. 3, No. 4, 46, 2002.
6. Karalis, A., J. D. Joannopoulos, and M. Soljačić, "Efficient wireless non-radiative mid-range energy transfer," Annals of Physics, Vol. 323, No. 1, 34, 2006.
7. Liu, Y., et al., "An overview of regulation topologies in resonant wireless power transfer systems for consumer electronics or bio-implants," Energies, Vol. 11, No. 7, 1737, 2018.
8. Lu, F., H. Zhang, and C. Mi, "A two-plate capacitive wireless power transfer system for electric vehicle charging applications," IEEE Transactions on Power Electronics, Vol. 33, No. 2, 964, 2018.
9. Sample, A. P., D. T. Meyer, and J. R. Smith, "Analysis, experimental results, and range adaptation of magnetically coupled resonators for wireless power transfer," IEEE Transactions on Industrial Electronics, Vol. 58, No. 2, 544, 2011.
10. Zhang, Y., Z. Zhao, and K. Chen, "Frequency-splitting analysis of four-coil resonant wireless power transfer," IEEE Transactions on Industry Applications, Vol. 50, No. 4, 2436, 2014.
11. Liu, S., J. Tan, and X. Wen, "Modeling of coupling mechanism of wireless power transfer system and vibration phenomenon of receiver-coil in three-coil system," AIP Advances, Vol. 7, 115107, 2017.
12. Liu, S. and J. Tan, "Study on the vibration mechanism of the relay coil in a three-coil WPT system," Progress In Electromagnetics Research M, Vol. 70, 117, 2018.
13. Huang, R., et al., "Frequency splitting phenomena of magnetic resonant coupling wireless power transfer," IEEE Transactions on Magnetics, Vol. 50, No. 11, 1, 2014.
14. Duong, T. P. and J. W. Lee, "A dynamically adaptable impedance-matching system for midrange wireless power transfer with misalignment," Energies, Vol. 8, No. 8, 7593, 2015.
15. Xiao, C., "New insight of maximum transferred power by matching capacitance of a wireless power transfer system," Energies, Vol. 10, No. 5, 688, 2017.
16. Luo, Y., et al., "Enhancing the robustness of the wireless power transfer system to uncertain parameter variations using an interval-based uncertain optimization method," Energies, Vol. 11, No. 8, 2032, 2018.
17. Kim, J., et al., "Efficiency analysis of magnetic resonance wireless power transfer with intermediate resonant coil," IEEE Antennas Wireless Propagation Letters, Vol. 10, 389, 2011.
18. Zhang, F., et al., "Relay effect of wireless power transfer using strongly coupled magnetic resonances," IEEE Transactions on Magnetics, Vol. 47, No. 5, 1478, 2011.
19. Liu, S., J. Tan, and X. Wen, "Dynamic impedance compensation for wireless power transfer using conjugate power," AIP Advances, Vol. 8, 025210, 2018.
20. Liu, S. and J. Tan, "Dynamic impedance compensation forWPT using a compensator in a three-coil wireless power transfer system," Circuit World, Vol. 44, No. 4, 171, 2018.
21. Biot-Savart law, https://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law.
22. Helmholtz coil, , https://en.wikipedia.org/wiki/Helmholtz_coil.