| Wireless power transmission technology has found ways to supply power for applications which are not suitable or convenient for towing wires. While the technology is exploiting its advantages in these applications, many revolutions have been achieved in the field of high power and high efficiency power transmission. These theoretical analysis and system level design, however, are proposed under the premise of non-metal interferences inserted in between the coils. Once the system is interfered by metal obstacles, the electromagnetic parameters of the system would change which would bring impacts on system performances. This problem should be carefully considered especially for cases in magnetic resonant wireless power transmission system, which is sensitive to resonant frequency disturbances. The temperature rise in metal obstacles may even cause danger. In order to study the disturbances bring by metal obstacles in wireless power transmission system, this paper carried out following works on the problem.(1) The paper analyzed the changes in space magnetic density distribution of wireless power transmission system caused by metal obstacles. The rules and mechanisms of variations in system coil equivalent inductance, quality factor, transmission efficiency and eddy current loss in metal obstacles are analyzed.(2) Taking metal interferences in magnetic resonant wireless power transmission system as an example, finite element model based on iron, aluminum and copper obstacles are built. The parameters of the system with metal obstacles under different positions are compared. The results show the most significant difference among these metal materials lies in the difference among its permeability.(3) By varying material permeability setting, the impact of metal permeability changes are simulated on the basis of typical metal obstacles analysis. The difference among system quality factor, resonant frequency, space magnetic field distribution, system transmission efficiency and eddy current loss in obstacles caused by permeability variations are compared. The results proved the correctness of aforementioned analysis.(4) A prototype investigating metal interferences in magnetic resonant wireless power transmission is established on the basis of theoretical analysis. The parameters of the prototype are the same with the parameters in the simulation model. System waveforms, resonant frequency, transmission efficiency, and eddy current temperature rise with metal obstacles under different positions in the system obtained by experiment are studied and compared with simulation results. The experimental results show great consistency with analytical model.The paper studies the impacts of metal obstacles to wireless power transmission system and its mechanism. Detailed analysis of interference differences in system performances among different metal material are carried out. The results show that the eddy current effect in metal obstacles is the key factor in disturbing system parameters. When metal obstacles are inserted at the middle between the coils, the metal obstacles draw the least influence to the system. The highest transmission efficiency of the system inserted with aluminum board, copper board and iron board are 43.62%,44.72% and 2.31% respectively. The permeability differences among metal materials are the most significant parameters in disturbing the system performances.
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