| Wireless power transfer(Wireless Power Transfer,WPT)technology has many advantages such as flexible power supply,safety and good looking.But in the application of wireless charging urban rail vehicles,there are different materials and different shapes of metal around the vehicles,and the power transfer environment becomes complicated.Due to eddy current effect and magnetic effect,these metal bodies in alternating magnetic field will produce eddy current loss,change the original magnetic field distribution of the system,lead to changes in coupling mechanism parameters,and make the analysis of system output characteristics and electromagnetic heat become difficult.Therefore,it is of certain significance for system analysis and design to study the wireless charging urban rail vehicles in complex metal environment,explore the influence law of metal on coupling mechanism,and study the electromagnetic heat and electromagnetic safety of the vehicle.Firstly,the SS compensation topology is analyzed by the mutual inductance equivalence theory,and the transmission characteristics and impedance characteristics in free environment are deduced by the circuit principle,also,the expressions of power and efficiency are obtained.The disadvantages and conditions of frequency splitting are pointed out and verified by Matlab.Using Loose equivalent model,the expressions of equivalent resistance,equivalent inductance and mutual inductance of coils in metal environment are deduced.Compared with the values in free environment,the values tend to increase,decrease and decrease,respectively.Due to magnetic effect,the effect of ferromagnetic metal on the system is analyzed qualitatively,and the result shows that magnetic effect can increase self-inductance.The final parameters of coupling mechanism are determined by eddy current effect and magnetic effect.Secondly,the finite element method is used to analyze the magnetic field distribution characteristics of the coupling mechanism,the shape of the DD coupling mechanism is selected,and the reversed direction of the current on the adjacent transmitting coils is specified.Then,the influence of metal on the frequency response characteristics,coil parameters,output characteristics and electromagnetic environment of the coupling mechanism is analyzed and summarized.The analytical methods and results can be applied to other planar coupling mechanisms.After that,the design suggestion for wireless charging urban rail vehicle is put forward,that is,the coupling mechanism should be placed under the chassis of the vehicle,because the impact on the system is minimal when the metal is located outside the receiving coil.Vehicle chassis materials avoid iron material,because ferromagnetic materials in the alternating magnetic field of eddy current loss,than non-ferromagnetic metal eddy current loss.Finally,based on the analysis of coupling mechanism,the electromagnetic heat of wireless charging urban rail vehicle is analyzed.The vehicle model is established,the structure of bogie,windshield,and steel bar is taken into account,and the distribution cloud map of the magnetic field environment inside and outside the vehicle is drawn.Compared with the international standards,the windshield has the possibility of exceeding the standard,which needs to be paid attention to.Then the eddy current and temperature rise of the metal parts of the vehicle are analyzed,and the temperature rise of bogie,steel bar and car body is simulated after working for five hours.By comparing different slotting positions,it is pointed out that slotting should avoid cutting the corresponding area of coupling mechanism and avoid vertical tangent between slotting direction and eddy current direction.In view of the excessive magnetic field of the windshield,the electromagnetic safety design of the windshield is carried out to ensure the safe operation of the vehicle.Finally,the simulation is verified by field measurement. |
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