Transfer Efficiency Analysis And Frequency Stabilization Control For Wireless Power Transfer Via Magnetic Resonance Coupling

Based on the theory of the near-field coupling,the technology of power transfer via magnetic resonance coupling transfers energy wirelessly.Magnetic resonance coupling wireless power transfer(MRCWPT)system has a lot of advantages such as middle transfer distance,relatively large power transfer,higher efficiency and non-radiation characteristics and so on,so it is suitable to charge every power level application.In that case,many researchers focus on this technology.However,MRCWPT system is easy to be affected by the ambient electromagnetic conditions.It may cause frequency detuning of the coils,the change of the mutual and the change of the inner resistance,which will lower the transfer efficiency.To improve the transfer efficiency of the MRCWPT system,this paper analyzes the influencing factors of the transfer efficiency and proposes a new dual-side independent frequency stabilization control strategy.Firstly,circuit theory and coupled mode theory are respectively used to describe the MRCWPT system.The research shows that weak coupling between two coils is basically required in the MRCWPT system.The differences between the inductive coupling wireless power transfer(ICWPT)system and the MRCWPT system are also compared by analyzing the transfer efficiency and power transfer.Besides,the affects of the frequency detuning of the coils are studied by defined the generalized detuning factors.The mutual of two coils in different position and the influencing factors of the transfer efficiency are introduced as well.Secondly,it is found that when the system is resonant,the phase difference between the source and the capacitor is 90 degrees in the transmitter coil,the output power gets maximum in the receiver coil.According to the characteristics,the dual-side independent frequency stabilization control strategies of the transmitter coil and the receiver coil are introduced in detail.The principle and structure of the adjustable capacitor are also studied.Additionally,the parameter design is also shown.Lastly,50 kHz MRCWPT system was built to further verify the effectiveness of the proposed strategy.There are practical experimental results under different conditions as follows.In the first experiment,the transmitter coil and the receiver coil are placed close.The transfer efficiencies are 91.1% at 10 cm and 80.08% at 20 cm,which is 6% higher than the existing technologies.In the second experiment,the transfer distance is fixed at 50 cm,and the experimental transfer efficiency is 51.62%,which is 4% higher than the existing technologies.Especially in the last experiment,two coils are placed side by side,the experimental transfer efficiency can be maintained at 76.37%.Such experiment hasn't been seen at present.All the results show that the proposed control strategy is reliable and effective.