| Due to eliminating the stator core,axial flux permanent magnet(AFPM)motors are featured with these advantages: high efficiency,no cogging torque,small armature reaction,less rotor loss,strong overload capacity and compact structure.Hence,they have important application value in the drive and generation system of electric vehicles,in the electric propulsion system of aircraft and in the servo system of spaceflight.A new electromagnetic topology of AFPM motor with concentrated ironless winding is put forward.Exploration for this type of motor is studied in the design of the ontology theory and optimization method,the cooling method of the stator with oil immersion,loss calculation and efficiency optimization,high-speed high strength rotor structure of Halbach PM array and high efficiency control with sine wave current.The theory and design of AFPM motor with ironless stator are analyzed and verified by simulation and experiment.Meanwhile,a new type of AFPM self-bearing motor and its control are proposed and demonstrated.This dissertation expounds the basic concept of ironless stator PM motor and the principle of torque generation,as well as the progressive evolution.Furthermore,according to the principle of magnetic circuit,ironless stator PM motors are divided into three categories: radial flux type,linear type and axial flux type.Based on the problem of large current pulsation in armature windings due to low inductance characteristics when driving ironless stator PM motor,a variety of control methods are compared.Finally,the basic characteristics and key problems of this type motors are summarized.And,the research contents and significance of this dissertation are explained.The basic topologies of ironless stator AFPM motor are briefly summarized.Based on existing problems of further development and application for ironless stator AFPM motors,a new AFPM concentrated winding motor with ironless stator are put forward for two key technical points.One is the winding coil molding and heat dissipation,and the other one is PM rotor design for air-gap field with high degree of sine.The design of ironless stator winding,Halbach PM array rotor disc with highly sinusoidal field and the size equation considering structural strength are presented.By three-dimensional finite element analysis(3-D FEA),the electromagnetic characteristics of AFPM CW motor with ironlss stator are analyzed in detail,including the magnetic field distribution,the end leakage characteristics and torque-current feature.9-slot/8-pole and 12-slot/10-pole prototypes are developed.The experimental results verify the validity of the theoretical calculation and simulation analysis,which laies the foundation for design and optimization of this new type motor.The mechanism of high frequency alternating current(AC)loss of the winding for ironless stator AFPM motors is analyzed in detail.The influence of the weight of high frequency AC loss and direct current(DC)loss on the total loss of the winding is obtained.The eddy-current loss of Litz conductor is calculated accurately by using the simplified equivalent winding model under the three-dimensional field distribution condition,which provides the reference for optimal design of loss and efficiency.In addition,the thermal analysis of stator windings under oil-immersed cooling condition is carried out,and the temperature test of the windings under different operation conditions was completed.The basic structure design of the ironless stator AFPM motor is presented.The force properties of the stator winding,PMs and the back yoke of rotor are analyzed.A reasonable stator winding structure of supporting and sealing are developed,as well as a novel enhanced structure of rotor disc with Halbach PM array.The electromagnetic and thermal multi-physics field coupling analysis model is built.The thermal stress distribution of winding supporting parts and the stress of the rotor and its support components are calculated and analyzed.Based on the FEA results,the optimization of the sheath of PMs and interference of the disc rotor are carried out.The structural design defect of the damaged rotor of the 9-slot/8-pole prototype under high-speed operation is explained.The high-speed rotor strength test of 12-slot/10-pole prototype under the cold and hot working conditions is completed at 9000r/min.The current fluctuation mechanism of low inductance PM motor under PWM control is analyzed.Based on the theory of three-phase full bridge inverter with output LC filter,a new control method of low inductance PM motor is proposed.The MATLAB model of control system for 9-slot/8-pole ironless stator AFPM motor is established.The simulation results show that the control system and the control strategy is a valid approach.The preliminary experiments demonstrate the effects of the drive system of current closed-loop control for low inductance PM motor.Starting from the basic principle of the bearingless PM motor and combining the ironless stator AFPM motor,a new type of self-beraing AFPM motor is proposed.The design method and integration theory of motor torque windings and levitation force windings are studied.This dissertation derived the calculation formula of levitation force and torque.A 3-D FEA model is established,and the simulation results verify the validity of the theory of the self-beraing AFPM motor.Furthermore,a control method of torque and levitation force is proposed,and the integrated control method of levitation current and torque current is verified by the simulation of Maxwell+Simploer field-circut coupling anasysis. |
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