Research On Key Technologies Of High Torque Density Axial-Flux Permanent Magnet Machine For Electric Vehicle Traction Applications

This dissertation focuses on the field of drive motors for electric vehicles and explores the application prospects of axial-flux machines in centralized drive systems and distributed drive systems.In response to the requirements of high power/torque density in electric vehicles,this dissertation selects two types of motors as the research objects: interior permanent magnet dualrotor single-stator axial-flux permanent magnet machine(AFPM)machine for centralized drive system and axial-flux hybrid excitation machine(AFHEM)for distributed drive system.Firstly,a comparative study of yokeless stator AFPM machines having fractional slot concentrated windings(FSCW)and integral slot distributed windings(ISDW)for electric vehicle traction applications is carried out.Two yokeless and segmented armature(YASA)type AFPM machines equipped with fractional slot concentrated windings are designed and compared with two AFPM machines equipped with integral slot distributed windings through the finite element method,including torque/power density,flux-weakening capacity,etc.Finally,the guideline of winding selection of AFPM machines for electrical vehicle is given: the ISDWAFPM machine with IPM structure has the strongest flux weakening capability,which is more suitable for high-speed EV traction motor while YASA-AFPM machine has better torque/density which is more suitable for low-speed applications.Secondly,a high-speed and high-torque/power-density dual-rotor single-stator AFPM machine was designed for the centralized drive system.Meanwhile,grain-oriented silicon steel material is introduced to the AFPM machine with yokeless stator,and a design method is proposed for AFPM machines with grain-oriented silicon steel material.With the introduction of the grain-oriented silicon steel,the torque output capacity is improved to 3 % and the efficiency is improved to 0.4 %,while the high efficiency area is enlarged.Eventually,considering the cost of grain-oriented silicon steel,the prototype of dual-rotor single-stator AFPM machine with non-oriented silicon steel was manufactured for experiments.Then,a novel AFHE in-wheel motor is proposed for the distributed drive system.According to its excitation principle,three schemes are proposed,and the effectiveness is verified by finite element simulation.Based on the proposed 3-D finite element model of AFHEM,the flux-adjustment range,torque output capability,loss,temperature rise,etc.are verified.Based on the complex magnetic circuit of the AFHEM,a 3-D equivalent magnetic network(EMN)model is established.The air-gap flux density,flux linkage,back-EMF,torque and fault tolerance ability of the motor are solved through the EMN model and compared with the 3-D FEA to verify its validity and correctness.It is hoped to form a rapid design method for the new type of motor with complex structure of 3-D magnetic flux path property.Finally,based on the EMN model,the influences of the magnetic saturation on the excitation regulation capability of the proposed AFHEM are analyzed,which provides a guideline for the optimization design of the new AFHE in-wheel motor.Finally,an efficient calculation method for the new AFHE in-wheel motor based on a 3-D equivalent magnetic network model is proposed.The air-gap flux density,flux linkage,backEMF,torque and fault tolerance ability of the motor are solved through the EMN model and compared with the 3-D FEA to verify its validity and correctness.A rapid design method for motors with a complex structure with 3-D magnetic field characteristics is obtained.Finally,based on the 3-D equivalent magnetic network model,the influence of the saturation of the equivalent permeances on the main magnetic flux path on the excitation regulation characteristics of the motor is analyzed,to provide ideas for optimizing the size of the key parts of the motor.