Research On Wireless Charging System With Staged Constant Current And Constant Voltage Output Characteristics

Compared with the traditional wire-type charging technology,the wireless charging technology has the advantages of safety and reliability,flexible power supply,and strong environmental adaptability.Based on the theory of magnetic coupling resonant wireless power transmission,this paper studies the staged constant current and constant voltage charging of electric vehicles,aiming to further improve the transmission efficiency of the system under the conditions of ensuring that the output voltage and current of the system are stable.Firstly,the loosely coupled transformer theory is used to model and analyze the four compensation topologies of the magnetic coupling mechanism: series-series,series-parallel,parallel-series and parallel-parallel.Analyze the function curve of its trans-conductance gain,voltage gain,current gain,and resistance gain with switching frequency through MATLAB software,and find the operating frequency points where the output voltage and current have nothing to do with the load change.Through the analysis of these operating frequency points,the series-series compensation topology is selected as the research object of this article,and the output power and efficiency characteristics of the series-series wireless power transmission system are studied.Secondly,the connection method,charging method and circuit model of the energy storage battery pack are introduced.According to the overall requirements of the system design,the first harmonic analysis method is used to analyze the circuit of the series-series type wireless power transmission system,and the relationship between the input impedance angle,the phase shift angle and the zero voltage switching angle is obtained.In order to realize the staged constant current and constant voltage output characteristics of the system,the operating frequency adjustment range and the phase shift angle of the system under the change of load and coupling coefficient are analyzed respectively,and the control strategy of variable frequency and fixed phase shift angle is proposed.This control strategy is not only staged charging can be realized and the zero voltage switching of the primary side MOS tube can be realized during the entire charging process.Thirdly,the resonant cavity parameter design method based on multiple boundary conditions determines the value range of the primary and secondary coil inductance,and uses ANSYS Maxwell software to select the shape of the coil and optimize the structure.The optimized design mainly includes the size of the inner radius of the coil and the addition of ferrite and aluminum plate materials.After the system component parameters are determined,the specific model selection of the main components in the circuit is carried out,and the specific working mode of the wireless communication module is introduced.Finally,with the help of MATLAB/Simulink software,a simulation model is built to verify the main circuit parameters and the control strategy of variable frequency and fixed phase shift angle.The simulation results verify the feasibility of the control strategy.On the basis of simulation verification,the software and hardware of the system were designed,and an experimental platform was built for experimental verification.Both simulation and experimental results show that the designed wireless charging system can not only realize the staged constant current and constant voltage output,but also realize the zero voltage switching of the primary side MOS tube,which is beneficial to improve the transmission efficiency of the system.