| In a magnetically-coupled resonant wireless power transfer(MCR-WPT)system,coils are used as the transmitter and receiver of electrical power,and the magnetic field is used as the power transfer media to efficiently carry out the transmission of electrical power in a medium and long distance.This technology has come into service in the fields of electrical vehicles(EVs),charging medical equipment and so on.High frequency alternating magnetic field exists inevitably in the air gap when the charging system works.In practice,foreign objects will occasionally fall into the magnetic field,and great impacts will be caused if they are not removed,especially metal objects.Metal objects exposed to high frequency alternating magnetic field generate heat rapidly,which is easy to cause fire,due to high frequency effects.At the same time,the existence of metal objects will weaken the magnetic field used for charging,resulting in charging failure and other serious problems.This paper will conduct further research on the detection and positioning technology of medium-sized metal objects in MCR-WPT system based on the charging system of electrical vehicles.In chapter 2,the influences of metal foreign objects on WPT system are studied using circuit and electromagnetic theory.Using the theoretical analysis method of electromagnetic field combine with electrical circuit,the high-frequency effects of metal objects in high-frequency magnetic field are analyzed.A conclusion is drawn that the magnetic field energy is partly consumed in the forms of heat dissipation and magnetized foreign metal,and the equivalent self-induction of transmitting coil changes,leading to the offset of the resonance point.Then,these effects are converted into relevant parameters,and they are used in the equivalent model built by simulation softwares to verify the theoretical analysis part.It lay a foundation for the design of the detection and positioning device.In chapter 3,based on the above analysis results,a foreign metal object detection and positioning device is designed.Firstly,the pros and cons of four commonly used metal object detection(MOD)methods are studied,and the method using balanced coil is selected because of its easy integration,high accuracy,simple structure and low cost.Then,combine with the traditional balanced coil and DQ detection coil,a new twodimension double-layer detection coil set with both detection function and positioning function is designed.The detection process is given,and its feasibility is verified theoretically.In chapter 4,the magnetically-coupled module in a WPT system with the new detection coil set is designed.Firstly,frequency characteristics of the magnetically-coupled module are analyzed,owning to the high dependence of transmission power and transmission efficiency on frequency.The tuning method of the system and the conditions of frequency-splitting are obtained,and the parameters of the transceiver are designed according to the theoretical analysis results.Then finite element analysising method is used to design the detection coil parameters,and the optimal solution is obtained when the width ratio of two DQ coils is 1.585.Comming next,the principle of correction circuit,filter,amplifier and rectifier in the conditioning circuit are studied using the knowledge of power electronics technology,and the parameters are designed with the help of simulation softwares.Finally,in chapter 5,an equivalent circuit model and a MAXWELL 3D model are established with the help of Multisim and MAXWELL.Basic parameter tables are created according to the parameter design of each part,and different certain parameters can be adjusted according to the requirements of each experiment.Through simulation experiments,the correctness of the theoretical analysis and the rationality of parameter design are verified,as well as to verify the feasibility of detecting and positioning function of the detection coil set to metal objects with different materials and location. |
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