Research On Efficiency Optimization Of Electric Vehicle Wireless Charging System Based On Impedance Matching

Compared with fuel vehicles,electric vehicles have been vigorously promoted by various countries due to their advantages in energy saving and environmental protection.The wired charging method of electric vehicles has problems such as potential contact safety hazards and fewer charging places.Compared with the traditional wired charging method,the wireless charging method has the advantages of no contact,flexibility,and convenience.Since the characteristics of the electric vehicle battery change during the system work process,the system will be detuned.In order to improve the stability and transmission efficiency of the system,the impedance matching technology is used to perform impedance transformation on the battery load to eliminate the battery impedance change caused by the system.Impedance matching plays a vital role in improving the transmission performance of the system.At present,the commonly used impedance matching methods include passive impedance matching and active impedance matching.The impedance matching method based on frequency tracking control proposed in this paper has less calculation and simple control.It can change the operating frequency of the system according to the change of battery load characteristics and improve the transmission efficiency of the system.The main work of this paper is as follows:(1)This paper conducts a theoretical analysis of the electric vehicle wireless charging system.Based on the working principle of the electric vehicle wireless charging system,the resonant compensation network is modeled by the coupled mode theory and the circuit theory respectively.Taking series-series resonance topology as the research object,derive the expressions of system output power and transmission efficiency.For pure resistive loads,the expression of the optimal load resistance of the system is deduced.Taking into account the nonlinear components in the system,the expression of the equivalent load is deduced,the relationship diagram of important parameters is established,and the impedance characteristics of the lithium battery are analyzed.(2)The principle of impedance matching is analyzed.Aiming at the problems of discontinuous adjustment of parameters and slow adjustment speed of the impedance matching method of the relay switch array,a frequency tracking-Boost-Buck combined impedance matching method is proposed.This method is to add a Boost-Buck impedance matching network between the receiving end and the load.The frequency tracking strategy enables the output voltage frequency of the high-frequency inverter to track the current frequency of the receiving end of the system.When the battery impedance changes and the system is detuned,Make the receiving end of the system return to the resonance state,adjust the duty cycle of the switch tube in the Boost-Buck converter to make the equivalent input impedance of the system equal to the optimal load resistance,so as to achieve the maximum efficiency transmission of the system.(3)An electric vehicle wireless charging system simulation platform is built in Matlab/Simulink simulation software,and build an MCR-WPT system experimental platform.The wireless power transmission system with a load of resistance or battery is simulated respectively.When the load is a battery,compared with the system without impedance matching link,the transmission efficiency of the system with Boost-Buck resistance matching link is increased by 6%.Compared with the system with only Boost-Buck impedance matching link,after adopting the frequency tracking strategy,the transmission efficiency of the system is increased by 14.6%,and the average increase in actual measurement is 14.2%.Simulation and experiment results show that the method proposed in this paper can improve the transmission performance of the system,which verifies the feasibility of the impedance matching method.