Research On Electric Vehicle Wireless Charging Control System

With the development of wireless power transfer(WPT)technology,WPT technology has been applied to aerospace,industry,transportation and other areas with its advantages of safety,reliability,and convenience.Among them,as one of the means of transportation,electric vehicle(EV)has become a typical respresentative of the application of WPT technology in the transportation area.The development of EV is one of the effective ways to reduce environment pollution and alleviate energy pressure.However,the main reason for limiting the development of EV is that the limited capacity of energy storage devices cannot satisfy the endurance requirement,and the power utilization rate of its wireless charging system is not high,and the charging problem has always been a huge trouble.The design of compensation network,the formulation of charging control strategy,and the requirement of charging srandard will affect the power output of EV wireless charging stysem.Therefore,in order to realize the constant current(CC)/constant voltage(CV)charging methods of the EV wireless charging system,and to further improve the charging efficiency,aspects of the magnetic coupling mechanism,compensation network and charging control are researched in this paper.Firstly,based on the system diagram of the DD(Double-D)coil structure,the equivalent model of the S-S topology is analyzed,and the relationship between the maxmum transmitting efficiency and the mutual inductance of the transfer coils is given,and the influence of the mutual inductance on the transmitting efficiency is analyzed.In order to reduce the use of the magnetizer material on the premise of not reducing the magnetic coupling capability of the transfer coils and sacrificing the transmitting efficiency,the finite element optimization simulation of the flat magnetizer of the DD coil during the offset process is carried out by using softwave ANASYS MAXWELL,and an H-shape magnetizer is obtained.Secondly,the S-S type wireless charging system circuit is given,the S-S type compensation network is theoretically analyzed,and the output current expression of S-S type compensation network is obtained.After adding passive components to the S-S type compensation network,the LCL-S type compensation network is obtained,and the output voltage expression of the LCL-S type compensation network is derived.After analyzing the characteristics of the output current and output voltage of the S-S type and LCL-S type compensation networks respectively,the two compensation networks are combined into a composite compensation network in the form of switches.Based on the composite compensation network wireless charging system,the expressions of charging current/voltage and transmitting efficiency are derived,and the condition for maximizing transmitting efficiency is obtained.Combined with the DC-DC circuits of the primary and secondary sides,the control strategy of CC/CV charging and transmitting efficiency optimization is proposed.The output characteristics of the composite compensation network and the feasibility of the charging control strategy are verified through the simulation.Besides,based on the LCL-S type compensation network based on previous research,the output current and output voltage of the primary and secondary DC-DC circuits are derived and analyzed,and the condition for realizing the CC/CV charging and transmitting efficiency optimization is obtained.Furthermore,a double side independent control strategy using disturbance control on the primary side and Proportional-Integral(PI)control on the secondary side is proposed.The superiority of the proposed charging control strategy is verified through the comparison between the simulations of the secondary side PI control and double side independent control.Finally,combined with the theoretical analysis of the wireless charging system,the experimental device selection and calculation,transfer coils design,system hardware and software design are carried out.A experimental platform is set up to carry out the mutual inductance estimation experiment of the magnetic coupling mechanism,the CC/CV charging experiment of the composite compensation network wireless charging system and the double side independent control CC/CV charging experiment.The experimental results show that the composite compensation network wireless charging system has CC/CV output characteristics,and the maximum transmitting efficiency has reached more than 80%.In addition,the LCL-S type compensation network wireless charging system under bilateral independent control also realizes the CC/CV charging and transmitting efficiency optimization.