| Wireless power transfer technology is an emerging frontier technology for Electrical engineering, the wire aging, point discharge,and sparks can be solved by using wireless power transfer technology. The wireless power transfer system can transfer energy via the magnetic field. The wire can be cutted between the transmitter and receiver. It is very fit to transfer power in harsh environments. However, the transfer efficiency of the wireless power transfer is low, which hinder popularization and applications of this technology. There are many problems in the aspects of improving the transfer efficiency, which are urgent to breakthrough.First, the several ways of wireless power transfer are presented. the wireless power transfer system via coupled magnetic resonances is chose in this paper. Secondly, the research status of this system is analyzed. Then we obtain that the efficiency is a key problem in this system. Finally, focusing on this problem, the research from the system Structure and adjusting methods as below are study.1. The efficiency is very low because frequency spilt phenomenon occurs when the WPT system operates in the over-coupling state. In this paper, the expression for the relationship between the efficiency,the input impedance and the operating frequency is derived by equivalent circuit theory(ECT). The frequency splitting phenomenon is analyzed. The effect of key parameters on frequency splitting and efficiency are obtained. A method of adjusting the parameters is proposed. The L-match network is used in order to adjust the equivalent load resistor. Frequency splitting phenomenon can be suppressed and the efficiency can be improved by the proposed methods. Finally, a wireless power transmission system via magnetic resonance coupling is designed and created. Simulation and experimental results have verified the validity of the theory.2. Transmission efficiency will be reduced when transmission and receive coils are aligned non-coaxially in the wireless power transfer system via coupled magnetic resonances. The expression for efficiency of the system is derived by using coupled-model theory(CMT). The variation of transmission efficiency is analyzed based on the expression for efficiency of the system. In this paper, the method of adjusting the parameters based on chaos optimization algorithm is proposed. The efficiency can be improved when key parameters of system are matched using that method. A wireless power transmission system via magnetic resonance coupling is designed and created. Simulation and experimental results have verified the validity of the theory.3. The intermediate coils system is presented based on the trandtional four-coil structure, the expression for the efficiency of intermediate WPT system is obtained by applying coupled-mode theory(CMT).in order to optimize efficiency of the proposed system, three optimization method is proposed. Simulation and e xperimental results validate the proposed optimization method.4. A novel four resonator coils structure is presented to improve system efficiency. Compared to the conventional four resonator coils structure, its source and load coils are also designed to have high loaded-Q(quality factor) and maximum cross coupling coefficients. Therefore, the source and the load coils also take part in the coupled-resonance with opposite-side resonators. This provides additional energy exchange paths. In order to prevent frequency splitting and obtain optimum efficiency, a method of coordinating the load resistor and operating frequency is proposed. The theoretical analysis and experimental results demonstrated that the proposed coil structure and method can increase syst em efficiency effectively.5. Low efficiency resulting from resonant frequency drift is a main obstructing factor for promoting this technology. In this paper, a novel method of coordinating the operating frequency and load resistor is proposed to prevent frequency drift. The system efficiency and input impedance are obtained by solving the system equivalent equations. In addition, the new resonant frequencies can be obtained by solving the input impedance equations. The new resonant frequencies are not only dependent on the parameters of the coil.But also depend on the load resistor. When resonant frequency drift occurs, the system can now operate at the resonant state and the efficiency can be improved by using the proposed method. Simulation and experimental results validating the proposed method are given.In the end, the main innovations of the dissertation are summarized, and the fields for further investigation are expected... |
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