Research On Maximum Efficiency Tracking Of Wireless Power Transfer Adapting To Coupling Coefficient Variations

Due to the safety,convenience and relatively long transmission distance of magnetically coupled resonant wireless power transfer method,it has been widely concerned and applied in the fields of electric vehicles,consumer electronics,unmanned Automated Guided Vehicle(AGV)and implantable medical devices.However,the efficiency of the wireless power transfer system is greatly influenced by the coupling coefficient between the transmitting and receiving coils and the variation of the load when actually supplying power to the load.In order to improve the efficiency of the wireless power transfer system under the variations of the load and coupling coefficient,this thesis adopts Semi-bridgeless Active Rectifier(SAR)and Switched-Controlled Compensation Capacitor(SCC)on the basis of Series/Series(S/S)resonant compensation network and combines with coupling coefficient estimation to achieve the maximum efficiency tracking control,the main research contents are as follow:Firstly,a mutual inductance equivalent model of the coupling coil is established to analyze the conditions at maximum transmission efficiency.By comparing the characteristics of the basic resonant compensation network,the S/S compensation network is used as the research object and its system characteristics are analyzed to investigate the main factors affecting the transfer efficiency.Secondly,based on the analysis of the advantages and disadvantages of active and passive impedance matching circuits,the SAR is chosen as the structure of the maximum efficiency tracking circuit in this paper,and its four operating modes are analyzed in detail,and the relationship between the on-state angle and the equivalent impedance at the receiver side is derived;the modulation effect of the SCC on the capacitor is used to compensate for the effect of the imaginary part of the SAR equivalent impedance,and the relationship between the SCC phase angle and the equivalent capacitance value is given.The circuit topology for maximum efficiency tracking is obtained by combining the modulation effects of SAR and SCC.Then,the variation of the mutual inductance parameter of the coupling coil with the transmission distance and the offset degree is analyzed from the theoretical derivation and finite element simulation.To deal with the problem that the variation of mutual inductance parameters affects the transmission efficiency,the coupling coefficient estimation and the constant voltage output control strategy combined with SAR circuit are adopted,and the simulation model built in MATLAB/Simulink verifies the effectiveness of the proposed control strategy.Finally,the experimental platform of the proposed control strategy is designed and built,and the main parts of the hardware and software of the system are presented.The experimental results show that the matching effect of the SAR circuit on the load enables the system to maintain high efficiency transmission over a wide range of loads.When the coupling coefficient is changed due to the increase of transmission distance or position offset,the changed coupling coefficient can be effectively estimated,and the transmission efficiency can be improved compared with that without coupling coefficient estimation.