| Wireless charging technology provides a new solution to the charging problem of electric vehicles and has become a research hotspot in recent years.At present,the main problem is that the offset of manual parking and the height difference of the chassis of the car in the static wireless charging process of the electric vehicle will affect the coupling factor of the coupling mechanism,which in turn affects the transmission efficiency and power of the wireless charging process,resulting in the instability of the charging process.In order to solve these problems,the anti-offset characteristic of the coupling mechanism is studied,and the impedance matching is studied on the power and efficiency instability caused by the offset of the charging coil and the change of load resistance.The main research contents are as follows:A structure of asymmetric planar spiral coils with better anti offset characteristic is proposed.Through electromagnetic theoretical calculation,it is found that for single-turn circular coils,the anti-offset characteristic of asymmetric coils with large primary coil and small secondary coil is better,and then a plane screw model commonly used for actual charging is built in Ansys Maxwell software,and it is found that this conclusion is also applicable to planar spirals,the anti offset characteristic of the planar spiral coils with a radius of 35 cm for the primary coils and 25 cm for the secondary coils is significantly better than those of the control group with both original and secondary coils radii of 25 cm or 35 cm.An impedance matching method that combines maximum efficiency tracking and maximum power tracking is proposed.The two can switch freely,meeting the dual requirements of wireless power transfer system for constant power and high efficiency.In SStype magnetically coupled resonant wireless power transfer system,there is an optimal load that maximizes the transmission efficiency of the system.When the coupling is weak,the output power of the system is high and the transmission efficiency is low,and the equivalent resistance of the load is changed by adjusting the duty cycle of the dual-tube Buck-Boost converter to make it equal to the optimal efficiency resistance for maximum efficiency tracking.When the coupling is strong,the frequency splitting phenomenon can’t be avoided by maximum efficiency tracking,and by analyzing the causes of the frequency splitting phenomenon,the maximum power tracking is proposed that by increasing the equivalent load of the system to make it equal to the expected power resistance,the frequency splitting phenomenon is effectively suppressed and the output power is improved.The switching point of maximum efficiency tracking and maximum power tracking is bounded by a coupling factor of 0.167,and the constant power output is realized by combining the closed-loop phase shift control of the inverter.The small signal model of the system is constructed by the extended description function method,the transfer function of the inverter phase shift angle to the output voltage is solved,and the zero pole is configured for correction,and the constant power control is realized through voltage closed loop.The MCR-WPT model is built in Matlab/Simulink,and the simulation results show that when the load changes from 2Ω to 5Ω,and the coupling mechanism is in the state of no displacement,horizontal displacement of 10 cm,vertical displacement of 5 cm,maximum displacement,the output power can be maintained at 3.5k W and the transmission efficiency is always above 89%. |
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