Research On Several Issues Of LCC-LCC Wireless Power Transfer System Of Electric Vehicles

The development and popularization of electric vehicles is an important means to alleviate environmental problems and resource pressures.With the advantages of safety and convenience,wireless charging plays an important role in solving the current charging and swapping problems faced by electric vehicles.This thesis starts from the basic problems of commonly used compensation structures and commonly used magnetic couplers for magnetic coupling resonant wireless power transfer.Aiming at the current urgent needs of electric vehicle wireless charging for dual-load power supply and high-precision foreign object detection,this thesis innovatively studies the dual-load synchronous wireless power supply technology based on fundamental wave and harmonic wave and the foreign object detection technology based on active double-layer array coils.The comparison of the characteristics of SS and LCC-LCC compensation structures is the first problem studied in this thesis.First,the principle of electric vehicle MCRWPT is analyzed and different types of compensation structures are introduced.Secondly,the mathematical models of SS structure and LCC-LCC structure system are derived respectively and the power and efficiency characteristics of the two are compared.The correctness of the deduction is verified by simulation based on Matlab/Simulink.Finally,the LCC-LCC structure is determined as the core structure of high-power power transfer,which lays the circuit foundation for the full text.The multiplexing of single-coil and double-D-coil magnetic coupler is the second problem studied in the thesis.First,single-coil magnetic coupler and double-D-coil magnetic coupler are studied separately based on the method of finite element analysis and simulation.Secondly,according to their respective coupling characteristics and offset characteristics,the application value of the single-coil and double-D-coil multiplexed magnetic coupler is studied.Finally,the geometric parameters of the coil is adjusted to simultaneously get a good coupling as well as a weak cross coupling among the power transfer coils within a certain offset range,which lays the foundation for the magnetic coupler for the following research.The dual-load synchronous wireless power supply technology based on fundamental wave and harmonic wave is the third problem studied in this paper.This thesis first analyzes the harmonics of the MCRWPT system and establishes a model of the dual-load synchronous wireless power supply system,based on which the current,power and efficiency expressions of each loop of the circuit is obtained.Secondly,under the condition that the parameters of the fundamental wave channel remain unchanged,the self-inductance and operating frequency of the coupling coil of the harmonic wave channel are studied to suppress the interference current introduced by the cross-coupling.The calculation found that the system parameter optimization has limited effect on system interference suppression,so an additional filtering inductance is used to further limit the interference current.Finally,the correctness of the theory is verified by the simulation of Matlab/Simulink platform.The foreign object detection technology based on active double-layer array coils is the fourth problem studied in this thesis.In this part,the RLC series circuit is used as an equivalent model of foreign object First,the principle of the foreign object detection baed on the active coil is introduced.Then this thesis focuses on the relationship between the electromagnetic characteristics of the detection coil and its shape,size,connection mode,etc.,based on which the structure of the detection coils is finallu determined to achieve the purpose of high detection accuracy and no blind spots.Finally,an experimental platform was built to conduct basic experiments of electric vehicle wireless charging system,dual-load synchronous power supply experiment,foreign object detection experiment and comprehensive system experiment.The results show that the system can achieve high efficiency and stable operation within a certain offset range,and can identify different kinds of foreign objects such as coins,paper clips,screws,etc.This verifies the correctness of the theory of dual-load synchronous wireless power supply and foreign object detection studied in this paper.