| With the development of modern electronics technology,there are more and more mobile electric devices in people's lives,from smart phones to electric vehicles,charging the battery of this equipment everyday is the inevitable task for people.The traditional wired charging mode has the disadvantages of mechanical aging,electric leakage and space occupancy,relative to this is the emerging wireless charging mode which can perfectly solve these problems,and it has higher practicability and safety.Based on the electromagnetic induction technology,a set of wireless charging system for battery constant current charging is designed in this paper.First of all,several common wireless power transmission modes and their latest research achievements are studied and compared in this paper,and the induction coupling technology(ICPT)is selected as the foundation of wireless charging system through analyzing their respective characteristics.The transmission mechanism of series-series(S-S)and seriesparallel(S-P)resonant compensation structures is studied by establishing the circuit model and mathematical deduction method.According to the research results,S-S structure is selected.The modeling analysis is carried out base on the S-S resonant compensation structure.The influence of the coil inductance and load resistance on the system parameters is analyzed by using the simulation software named Pspice,which provides a theoretical basis for the design of the system.Secondly,the magnetic field distribution of planar coil and cylindrical coil is simulated and compared by the simulation software named Ansoft Maxwell,the simulation results show that the planar coil is more suitable for the system.The magnetic field changes of the planar coils with different cores are analyzed,a planar coil with 8 cores is selected as the transmission coil of the system.The overall design of the system is carried out,the hardware part includes the inverter circuit,the power transistor protection circuit,the rectifier circuit and the control circuit.In order to achieve constant current charging,a control strategy based on PI algorithm for adjusting the working frequency and a Zigbee module for wireless communication are added to the system,closed loop control is realized.TMS320F28335 is selected as the control chip and the corresponding software program is designed.Finally,a wireless charging experiment platform with a power of 1k W is built.Carrying out the experiment which use lithium iron phosphate battery as a load,the changes of the voltage waveform during charging and the cause of theose changes are studied.An open loop charging experiment is carried out for the case that the transmission coil has a horizontal displacement or vertical displacement,the influence of the relative displacement of the coil on the system is studied.A closed loop constant current charging experiment is carried out,the experimental results show that when the coil spacing is 20 cm,the wireless constant current charging with power 1k W and transmission efficiency of 85.6% is achieved,basically meet the design requirements. |
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