Studies On Magnetically-Coupled Resonant Wireless Power Transmission System

With the continuously development of science and technology and the compression of human living space,the shortcomings of traditional power transmission methods are gradually exposing,the wire power transmission can’t meet people’s daily needs.Wireless power transmission technology can eliminate the electrical interconnections between the device and the power supply.Compared with the traditional power transmission method,it is more secure and flexible and can save more living space,which possesses stronger anti-interference ability.So it makes the electrical equipment get rid of the constraint of the power line so that people’s living has become more comfortable and convenient.First of all,this paper has been studied theoretically on the magnetically-coupled resonant wireless power transmission system by using the coupling model theory and circuit model theory,so as to obtain the general expression of system transmission efficiency.Based on the energy transmission principle,this paper expounds that when the power frequency is equal to the resonant frequency of the coil,the transmission efficiency of the system takes the maximum.It can be seen from the expression that the precondition of the system achieving to maximum transmission is that the electromagnetic resonance can be produced between the two resonant coils,which requires the power supply frequency to be maintained near the coil resonant frequency.According to the comparative analysis of the two theoretical models,we can have a much deeper understanding of the working principle of wireless power transmission,and it can lay a good foundation for the further study and analysis.Secondly,two commonly-used resonant coils(spiral resonant coils and planar helical resonances coils)are studied.This paper analyzes the calculation method of their parameters of inductance,capacitance and resistance,and it has a great influence on the resonant coil parameter design.It analyzes the effect of conductor skin effect and loss,quality factor,coupling coefficient and other factors on the transmission characteristics of the system.It is concluded that using large diameter and multi-stranded wire can effectively reduce the skin effect.Meanwhile,the key to improving transmission efficiency is to increase the coupling coefficient between the two coils.Besides,increasing the coil inductance can improve the quality factor in order to reduce the loss and improve efficiency.Thirdly,this paper uses HFSS simulation software to simulate the two resonant coils,and it is concluded that the system will get higher transmission efficiency when the power frequency is close to the resonant frequency;While increasing the resonant coil spacing,the transmission efficiency drops rapidly.Changing the relative position of the resonant coil,the transmission efficiency will not change a lot in a small range.When the horizontal offset distance exceeds 1/2 radius of coils,the transmission efficiency will be greatly reduced.When the axial angle of the coil is less than 30°,the transmission efficiency does not change much,but it will quickly drops to 0 when over.The simulation results show that the relay coil can greatly improve the transmission efficiency of the system.And simulation analysis been made on the case where the two transmit coils are used for radio transmission of one receiving coil.The simulation results show that the two transmit coils of the inverted phase can produce an effect of canceling on each other,and there is no energy transfer to the receiving coil.Similarly,the two transmit coils in the same phase will produce the effect of superposition.Finally,a simple system experimental model is designed according to the principle of magnetically coupled resonance,some detailed introduction to the launch device and the receiving device are also given.The core components of the model use the NE555 integrated circuit to produce the high frequency power required for resonance.The experimental device has basically realized the wireless power transmission in the 100mm transmission distance,and it can reach about 40%of the transmission efficiency.By changing the coil distance,the coil horizontal offset distance and the coil axial angle,measuring the electrical parameters of the system in different working conditions above and analyzing the measurement results,it proves the correctness of HFSS simulation analysis.And at the end of this paper,it puts forward some problems that exist in experimental facility and how to do the further research.