Research On Node-based Magnetic Resonant Wireless Power Transfer

Wireless power transfer is the technology to realize wireless transmission of electric energy by electromagnetic energy or electromagnetic wave.It has the advantages of good security,high reliability,low maintenance cost and strong environmental adaptability.In recent years,with the continuous upgrading of electronic devices,measurement and control technology,power conversion technology and other technologies,wireless power transfer has achieved rapid development.Applications of wireless power transfer have emerged in more and more fields,such as medical treatment,transportation,life,military,electric power,etc.Different application fields also put forward higher and clearer requirements for wireless power transfer.Magnetic resonance wireless power transfer is an innovational technology based on the principle of magnetic coupling resonance.It uses non-radiative magnetic field coupling to realize energy transfer,and its transmission efficiency can reach 80% at the transmission distance of double the resonant coil diameter.There is no need for accurate alignment between the sender and the receiver.The transfer also enjoys good penetrability.This dissertation focuses on magnetic resonance wireless power transfer.On the node-based system modeling,researches are carried out on the miniaturization design,stability control and reusability design.These studies aim at promoting the transformations of wireless power transfer into practical applications.Firstly,the resonant unit in transmission is defined as the transmission node.According to the active and passive characteristics of nodes,power transfer systems are divided into four categories: single-active single-passive,single-active multi-passive,multi-active single-passive and multi-active multi-passive.Different application scenarios and different implementation of wireless power transfer systems are classified.A node-based equivalent model for all kinds of systems is established,in which various resonant units and complex coupling relationships among in the system are simplified as circuit structures and component relationships.The complexity of system analysis is thus simplified,and the ease of design is improved.Although magnetic resonance wireless power transfer is mainly studied,this classification is also applicable to other types of wireless energy transmission classification.Secondly,the single-active single-passive power transfer in the closed medium environment is studied.Effect of frequency detuning is analyzed,and structure-controlled frequency tracking technology is proposed to enhance the stability of the system.The physical structures of the transmission nodes are also optimized,improving the power transfer efficiency of the system and providing a reference for the application of magnetic resonance wireless power transmission in medical implant devices with small size and high working frequency.Thirdly,two kinds of single-active multi-passive design schemes are proposed to tackle the problem of frequency splitting and insufficient transmission bandwidth respectively,in order to enhance system stability and reusability.The power transfer efficiency of the original resonant frequency decreases dramatically when the frequency splitting occurs.The parallel-auxiliary-node scheme is suggested thus to improve power transfer efficiency,without changing the node structures and transmission distance.Meanwhile,to meet the demand of the transmission bandwidth for simultaneous wireless information and power transfer,a relay-node design scheme based on the coupled bandpass filter theory is proposed.Through numerical fitting and calculation,the architecture of relay nodes can be realized,with better transmission bandwidth,data rate of information transmission and power transfer efficiency.Then,the mutli-band node structure is studied to simplify the design of multi-active multipassive power transfer system.In order to be compatible with different transmission standards,or to meet the demand of high received power,the system often needs to transmit energy in multiple frequency bands simulataneously.Mutli-band node refers to a kind of transmission node with two or more resonant frequency points,which can realize multi-frequency transmission,reduce crosscoupling between transmission nodes and simplify implementation.The design of dual-band nodes and the realization of dual-band impedance matching are discussed here with the method of equivalent resonant circuit.The L-shaped structure,stacking shaped structure and planar compact structure dual-band nodes have been designed successively.The power transfer and data transfer are analyzed between two dual-band nodes and between dual-band node and single-band node.The performance between the planar compact node and A4WP(Alliance for Wireless Power)device,and the influence of the spatial position of dual-frequency nodes and NFC(Near Field Communication)devices on the transfer of energy are also studied,providing an effective way for system integral design.Finally,previous work and research results are summarized and extended,pointing out the deficiency and the direction of future research for future exploration.