Magnetic Core Optimization And System Adjustment Of Wireless Power Transfer For Electric Vehicles

Based on the research background of high-power electric vehicle(EV)wireless charging,this paper discusses the high efficiency and high-power density of magnetic core in detail.According to the different application scenarios of both coil sides,starting from different requirements,the construction of efficient and highly integrated highpower vehicle wireless charging system,the multi-objective optimization design of the core structure at the transmitting side,the feasibility exploration of the novel core material at the receiving side,and the realization of the resonant self-adjusting wireless charging system are deeply studied,which provides a reference for the development of the industry.Firstly,considering the large-dislocation parking application scenario,the volume minimization requirement and the high-power density characteristics of the receiving side for the vehicle,the asymmetric DD reference magnetic couplers with strong antioffset performance and LCC-SP topology with constant current output characteristics are adopted in the 11 k W system scheme with current doubler rectifier control circuit.Through parameter dimension reduction,the parameter tuning design of the multidegree-of-freedom compensation topology is completed.The built 11 k W prototype achieved stable and efficient operation and the closed-loop adjustment of output power.Then,the relationship between the uneven distribution of the transmitter core’s magnetic flux and core loss is studied.Based on the equivalent magnetic circuit model,a new composite core structure is proposed as the optimization object,and the maximum coupling coefficient and minimum core loss are used as the optimization objectives to optimize the core structure.The optimal core structure’s parameters are obtained by using the non-dominant sorting genetic algorithm(NSGA-II)with elitist strategy,then the effectiveness of the optimized core is verified by experiments based on the built 11 k W system.At the same time,considering the conflict between the receiver application scenario and the fragility and low saturation of ferrite core,a nanocrystalline core with high saturation and high flexibility is proposed for receiver application.Aiming at the problem of high eddy loss of nanocrystalline core at high frequency,the eddy current is blocked by the improved heat treatment process and the staggered splicing process,and the permeability process boundary is determined by the homogenization modeling and simulation analysis.Finally,the feasibility and anti-saturation advantages of the nanocrystalline core scheme are verified through a variety of experimental analysis.Finally,to solve the system mismatch caused by frequent replacement of core and coil misalignment,using the special mechanism of the both compensation inductance in the LCC-LCC topology,the adjustable capacitance based on Pulse Width Modulation is introduced to indirectly adjust the value of compensation inductance,which fundamentally solves the problem of coil misalignment.Finally,the topological power circuit and the adjustable circuit are set up,and the adjustment effectiveness is verified by experiments under different mismatch conditions.Based on the above research,the three innovation points in this paper are summarized as follows:Innovation point 1: Based on the optimization technology of magnetic flux homogenization regulate under multi-objective and multi-constraint,to improve the transmission efficiency and core utilization of the coupler,an innovative multiobjective optimization method for a novel core structure is presented,which aims at maximizing the coupling coefficient and minimizing the magnetic flux uniformity.Innovation point 2: Based on the process optimization and stacking technology of anisotropic nanocrystalline core,starting from the requirements of high-power and small volume of wireless charging for EV,a new type of staggered splicing and stacking nanocrystalline core is innovatively adopted to replace the application of traditional ferrite core in vehicle side.Innovation point 3: Based on the resonant self-tuning technology of adjustable switching capacitor,considering the influence of different test conditions on the matching of system parameters,innovatively utilizing the special adjustment mechanism of compensation inductance in the double side LCC topology,the system detuning caused by the change of coil parameters is fundamentally solved from the compensation topology.