Study On Frequency-tracking System For Electric Vechicle's Wireless Charging System

It is not only economical but also environmentally friendly to replace the motor vehicle with electric vehicle(EV).And wireless power transmission(WPT)technology can achieve electrical isolation between power supply and load,and is safe,reliable,and flexible.Applying wireless power transmission technology to electric vehicles can enable electric vehicles to get rid of the constraints of charging cables.It is of great economic and scientific significance to propose a new wireless charging scheme for electric vehicles or to improve research in this area.At present,there are still some problems in the practical application of wireless charging technology for electric vehicles.For example,if the electric vehicle is not parked in place,it would be possible that the transmission performance of the system is affected by the change of the transmission distance or the offset between the resonance coils,and even the system power or efficiency would be greatly reduced.And,if the charging system is in an over-coupling situation,there would be also a decrease in system power or efficiency due to frequency splitting.Therefore,in view of the above problems,this paper proposes a frequency-tracking tuning control method that is suitable for a SS-type WPT system with two-coil structure to improve the misalignment tolerance of wireless charging system.Firstly,it is analyzed in this paper that the transmission performance of WPT system is affected by charging positions of EV via changing the mutual inductance of the coupled coils.And then,both the appropriate coupling mechanism and compensation network are selected to reduce the impact of charging position on transmission performance.Then,a system circuit model based on mutual inductance coupling theory is built and the frequency characteristics of the system are studied based on this.The study theoretically demonstrates the feasibility of improving the misalignment tolerance of wireless charging system by frequency tracking control.Therefore,the frequency tracking tuning control method that can improve the misalignment tolerance is further studied in this paper.Secondly,according to the principle of magnetic coupling resonant wireless power transmission,a set of experimental platfonn with frequency-tracking tuning control system and output power of 800W is set up.The platform mainly includes the main circuit part of the WPT system,the control system part and the docking circuit part.The control system is used to implement the specific design of the frequency-tracking tuning control method proposed in this paper on FPGA.Finally,a evaluation method of the system's misalignment tolerance is given,and the experimental platform is tested by experiment.As show as the results of the tests,on the one hand,the system's frequency-tracking speed is no less than 50kHz/s,which ensures that the system can respond to the rapid change of the charging position in real time;on the other hand,when the system is operating at full power with a 50? load and a 25cm air gap,the horizontal tolerance distance of the parameters(3%,3%)is not less than 20cm,and the efficiency is not less than 82%.