| While embracing the development of economy and the improvement of living, people starts to pursue some kind of more flexible, portable and elegant design for power supply. Being an emerging approach with these merits, magnetic coupled resonant wireless power transfer (WPT) technology can release from the bondage of electric cables and realize the wireless transfer of electric power. This WPT technology has gained extensive attention in virtue of its safety, convenience and aesthetics. An increasing number of application are emerging in industry, such as electric vehicles, portable electronic devices, implantable medical devices, monitoring equipments of electric power system, automation equipments, underwater instruments, etc.The security issues of WPT technology’s electromagnetic environment is inherent, and will inevitably attract public attention accompanied with the rapid popularization, which seeks the research of its working electromagnetic environment for a further promotion. On one hand, magnetic field is used to transfer energy and thus should be enhanced in the working region of the system. On the other hand, magnetic field on the outside of the working region needs to be reduced since it also could affect the biological health and other equipments. Therefore, shielding measures are necessary to reduce the magnetic field on the outside of the working region without interfering with the proper functioning of the system. The application of shielding measures will bring an impact on system parameter variations due to the coupling between the WPT system and the shielding devices. However, a WPT system epitomizes the kind of system which has multiple strongly interpretational parameters, which means, any tiny variations of the parameters will alter the working status, even making the system cannot working properly.Several electromagnetic problems are investigated in the dissertation to solve the above issues and minimize their adverse impacts. The dissertation intends to achieve the goal of keeping system working normally and restraining the electromagnetic radiation around the WPT system. System working principles in shielding environment is explored and the equivalent impedance model of system with shielding devices is established. In addition, the parameter compensation mechanism and restoration of system transfer efficiency methodology are discussed. System performance in the shielding environment is summarized according to the basic analysis. And the proposed methods are finally applied in a WPT prototype. The work of the dissertation is concentrated on following aspects:(1) Research on modelling of magnetic resonant WPT systemCoupled mode theory and equivalent circuit model are used to analyze the systems with single resonator, double resonators, relay resonators and power source load respectively. Corresponding numerical calculations of output power, power transfer efficiency and frequency characteristics are then derived. On the basis of fundamental research, the field-circuit coupled method is proposed to analyze the magnetic coupled resonant WPT system. Specific steps include:The system of partial differential equations is first discretized into algebraic equation set. Afterwards, the negligible electromagnetic parameters of the resonator which are ignored in regular WPT system are calculated. The values of each field parameter are further determined and the parameters of the resonator are obtained. Finally, the circuit model is utilized to identify the relationship between each field parameter. The field-circuit coupled method has laid solid foundation for further analysis.(2) Research on the influence of external environment on WPT systemImpedance model of resonator in metal environment is established based on the electromagnetic theory. The numerical expressions of inductance, mutual inductance and resistance of the resonating coil are educed. On the premise of these calculations, the impact of ferromagnetic material and non-ferromagnetic materials on the resonator parameters is analyzed comparatively. Simulation and experiments are carried out accordingly. Furthermore, the model of magnetic coupled resonant WPT system working in metal environment is established. Specifically, system with a symmetrical shield and an asymmetrical shield are presented respectively. The deviation regularities of both working frequency and system working conditions are derived. In addition, a shielding measure using the combination of ferromagnetic and non-ferromagnetic materials is proposed to maintain the similar system parameters regardless of different environment. The performance degradation is proved to be decreased to minimum.(3) Research on the influence of magnetic resonant WPT system on external environmentTake the wireless charging for electric vehicles as an example, distribution of electromagnetic field in free space is analyzed and the influence of system on human organs is calculated. The shielding functions of ferromagnetic and non-ferromagnetic are investigated respectively and corresponding distribution of electromagnetic field are derived by simulations. In order to realize the enhancement of electromagnetic field in working region and the decrease of electromagnetic field on the outside of the working region, optimization of the shielding measures using the combination of ferromagnetic and non-ferromagnetic materials is implemented.(4) Design and implementation of an experimental prototype of WPT systemSpecifically, adjustable high frequency power source with full-bridge structure and rectifier are designed. The correctness of theoretical analysis is then validated. Monitoring equipment of electromagnetic field is also designed to realize the visualization of electromagnetic environment, which contributes to the promotion of WPT technology. |
PDF Full Text Request