Research On Wireless Energy And Information Cooperative Transmission In Metal Environment

By using the spatial alternating magnetic field as the medium,wireless energy and information cooperative transmission technology can achieve the energy and information transmitting from the transmitter to the receiver through the coupling mechanism,and the energy and information can be separated by the demodulating unit at the receiver.Eddy currents are generated when the metallic body is in an alternating magnetic field,which not only cause eddy current losses,but also change the original magnetic field distribution and disturb the electromagnetic parameters of the transmission system.In many application scenarios,the surrounding metal environment of wireless energy and information cooperative transmission systems is often complicated,and the size,shape,distance and material of the metallic body are uncertain,such as the metal chassis of electric vehicles,the metal shell of medical implant devices,artillery and fuse nearby the gun assembly system.Since the wireless energy and information cooperative transmission system is a multi-parameter and parameter-sensitive system,the disturbance brought by the above metal environment may cause failure of the system energy and communication transmission,and even a safety accident.Therefore,it is of great significance to study the influence of metal on the transmission characteristics of the system and to construct an optimization mechanism,then to establish a wireless energy and information cooperative transmission system model in a metal environment.This research is derived from the project requirements of the passive induction setting system project from XX manufactory,and has been funded by the Focus Project of Chongqing for application and development “Key Technologies and Design of RFID System in Complex Metal Environment”,focusing on its key issues –the basic theory and method of wireless energy and information cooperative transmission to medium and small power applications under metal environment.The main contents of this thesis include:(1)The existing wireless power transfer model does not consider the influence of metallic body on medium and small power wireless energy and information cooperative transmission system.Aiming at this problem,this thesis studied the variation of coil aggregate parameters under metal environment from the electromagnetic field theory,and constructed a theoretical model of wireless power transmission system for metal environment.The finite element analysis method was used to realize the wireless power transfer modeling and simulation under free space and metal environment,so as to deeply understand the differences between the two environments on wireless power transmission performance and related influencing factors.Based on the analysis of these factors,different positions and different materials of the metallic body were designed to simulate the metal environment.The effects of the metal environment on the parameters of resonant frequency,input impedance,magnetic field distribution,eddy current losses,transmission power and efficiency in the wireless power transmission system were studied in detail.The law and mechanism will lay the foundation for the study of the regulation mechanism of subsequent system performance.(2)Under the influence of metal environment,the wireless power transmission system appears problems such as resonance frequency shift and transmission power degradation.The traditional fixed-frequency control system based on series-series resonance compensation is no longer valid,while the method of adjusting the resonant capacitance of the transmitter is not applicable due to high cost,large size,and difficulty in accomplishment.Aiming at this problem,this thesis first studied the structural characteristics of resonant compensation network and the basic principle of the current-fed class D power amplifier.On this basis,it focused on deriving the impedance frequency characteristics of the parallel-parallel resonant network and demonstrated that by using self-oscillating inverter,the system resonant frequency self-tracking and Zero Voltage Switching(ZVS)soft switching control mechanism can be realized by tracking the Zero Phase Angle(ZPA).Aiming at the problem that the original self-oscillating inverter has large driving losses and switching losses,and the output power is limited,the improved power controllable self-oscillating inverter was designed by improving the driving circuit and separating the driving and input source.It has been verified that the improved inverter can not only automatically track the system resonant frequency,but also significantly improve the system transmission power and transmission efficiency.Finally,it is verified that in a metal environment,the system can automatically track the resonant frequency and increase the transmission power and transmission efficiency by increasing the input voltage.(3)In view of the strict limitation of the receiver volume in application,a wireless energy and information cooperative transmission strategy based on single coil group was proposed without additional coupling mechanism such as coil and transformer.The strategy was based on the self-tracking characteristic of the self-oscillating inverter to realize energy efficient transmission,and the Binary Frequency Shift Keying(2FSK)modulation of energy was realized by switching the resonant capacitor of the transmitter,and the Binary Amplitude Shift Keying(2ASK)demodulation was realized at receiver according to the amplitude of the receiving voltage.In order to avoid the demodulation failure due to the resonant frequency shift caused by metal environment,the 2FSK modulation circuit model was established and the carrier frequency selection rule was given.The approximate relationship between the switching capacitor ratio and the modulation degree is derived and verified by simulation.Finally,the related physical model was built,and the performance of wireless energy and information cooperative transmission and the influence of the metal environment on the system information transmission were tested.The energy and information transmission of the system at 2kbps rate was realized within a certain range between the metal plate and coil.The relevant research results of this thesis have been successfully transformed and applied to the passive induction setting system project from XX manufactory,and achieved good results.