| Green electric vehicles have become the mainstream in the traffic field under the background of the oil shortage and the environmental protection.The fixed wired charging methods are presently adapted in electric vehicles.These methods have severe disadvantage,such as inflexibility,low efficiency and unsafety.Then,the wireless power transfer technology has superior advantages,such as point-to-multipoint,non-contact and high-efficiency.The wireless power transfer technology has attracting more and more researchers’ attention.Circuit compensation topology is taken as a theoretical basis in this dissertation,as the research goal,which improves the transmission stability of dynamic wireless charging systems of electric vehicles.The selection of compensation topology,transmission coil switching control method,and coupling coil optimization problems in the system are studied.The transmission performance of the whole wireless charging system in the best state is improved.The main research content and contributions of this dissertation are as follows:(1)A hierarchical solution is proposed for the selection of the system compensation topology.Firstly,the mathematical modeling and analysis of the four basic resonant compensation structures are carried out based on the loosely coupled transformer model.Secondly,four basic compensation topology transmission characteristics and system load relationships are constructed.Then,the coupling coefficient characteristics,load characteristics and frequency characteristics of the S-S compensation topology with great transmission characteristics are analyzed.The LCL-S compensation topology is analyzed.And the structure has the advantages of pure resistivity and constant output voltage when the secondary side is mapped to the impedance of the primary side,which is in line with the selection of the system constant voltage charging compensation topology.Finally,the output constant voltage characteristics of the LCL-S topology are verified by simulation.(2)A switching method for detecting the position of the primary current and control the primary transmitting coil is proposed for the instability output caused by the switching of the transmitting coil during the operation of electric vehicles.Firstly,the structure of the LCL-S dual transmitting unit is constructed.The expression of the relationship between the voltage and current parameters on the primary side is derived.The correlation between the compensation inductor current flowing through the primary side and mutual inductance is analyzed.Secondly,the primary side transmission coil switching is controlled by sampling the primary current.Finally,the proposed method can effectively improve the output stability of the system.And the proposed method has been verified by the simulation.(3)An optimization design method of shape coupling performance is proposed for the problems of multipoint-to-point primary and secondary side coupling coils.Firstly,equivalent models of coupled coils of different shapes are constructed.The expressions of mutual inductance functions between the same type of primary and secondary edges,as well as different types of coupling coils,are calculated.Secondly,the electromagnetic simulation is carried out under the condition of position distance offset between the same type and different types of coupling coils.Subsequently,the coupling performance magnetic cloud plot and the offset effect are analyzed.And the square-square coupling coil has superior coupling performance.Finally,the transmission stability between the square-square coupling coil and the primary transmitting coil during the dynamic process of the secondary receiving coil is verified by experiments.The structure has great coupling output characteristics that are indicated in the experimental results. |
PDF Full Text Request