| Wireless power transmission(WPT)technology transmission can effectively solve the problems caused by traditional cable power supply such as line aging,cutting-edge discharge,and spark generation.It has the characteristics of higher safety,reliability,flexibility and has become a widely researched object.Among them,the magnetic resonance wireless power transmission can carry out medium-distance transmission and has high transmission efficiency.It has a wide range of applications in wireless charging of electric vehicles,smart homes,underwater equipment,implanted medical equipment and wireless sensor networks.In recent years,magnetic resonance wireless power transmission technology has made certain progress in key technologies and difficulties.However,there is still a big gap to the actual large-scale application and there are still some problems worthy of further discussion and research.This paper has carried out more in-depth research on the performance optimization and stability of the magnetic resonance WPT system.The main innovative work is as follows.First,a design method for the optimization of WPT system performance based on two-port network and equivalent circuit theory is proposed.The two-port network modeling and analysis of WPT system are carried out.The theoretical calculation formula for optimal load impedance of WPT system performance is deduced,which provides a guide for practical applications.At the same time,the optimal design of the multi-port network is analyzed.The optimal load expression of the multi-transmitter or multi-receiver WPT system is derived.All the results are verified by simulation and experiment.Secondly,in view of the WPT system stability problem,the WPT system stability research based on frequency selection technology is carried out.The specific derivation and analysis of the working conditions corresponding to guarantee the stable output of the WPT system are carried out.The concept of the secondary resonance frequency is proposed.The system can maintain stable transmission efficiency and power delivered to the load at the secondary resonance frequency.Then,in view of the load change,the ABCD matrix is used to characterize the system performance and four independent load working methods are proposed.The theory is verified through the simulation and experiment.The result shows that a constant output voltage can be obtained at the operating frequency proposed by the theory.Then,two impedance matching techniques for WPT system are investigated.The impedance matching realized by introducing impedance matching network or relay coil structure are explored.By optimizing the three power gains simultaneously,the research explores the conditions for the WPT system to achieve the ultimate gain.And on this basis,the expressions of the components in the impedance matching network are deduced.By comparing single-port,dual-port matching and conjugate image impedance matching,the feasibility of dual-port matching was proved.The experiments were carried out to verify the point.On the other hand,the three-coil structure and the four-coil structure are explored to achieve matching through introducing the relay coils.The theoretical design of the coupling coefficient between the intermediate coil and the transmitting coil or the receiving coil is deduced.Research has found that the three-coil structure can only achieve a unilateral matching effect,while the fourcoil structure can achieve a double-ended matching effect.Finally,the wireless power transmission with anti-offset capability is explored.In view of the problems in the application of implanted medical device,a planar WPT system with antioffset capability was first proposed.The system adopts a planar hybrid array coil structure.By analyzing the magnetic field distribution of the structure,the working mechanism can be explained.The experimental results show that the structure can achieve stable transmission efficiency of the implanted receiving device in a large planar offset range.After further research,a 3D WPT system with anti-offset capability that can adapt to spatial angle changes is proposed.The system can be applied to the capsule endoscope and the two-dimensional receiving can realize the stable receiving efficiency of the capsule endoscope in a large angular offset range.The system has the characteristics of light weight,high efficiency,and strong anti-offset ability.The experimental results further prove that the system can improve the anti-angle deviation ability of the wireless power transmission system. |
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