Analysis Of The Field-weakening Performance Of Yokeless And Segmented Armature Axial Flux Motor

The yokeless and segmented armature(YASA)topology is a new type of axial flux permanent magnet synchronous motor.The YASA motor has less stator iron loss,no end windings,high filling factor,and a wide application range,especially to the applications of the finite size of shaft.Thus,the topology is highly suited for electric vehicles,renewable energy systems,flywheel energy storage systems and so on.The motor is characterized by the stator structure of yokeless and modular,which is composed of a number of identical small modules.The cores and shoes of small modules can be made of steel sheets stacked,or other new materials,such as soft magnetic composites(SMC),amorphous alloy.The windings are wound on the iron core through the insulation materials.The yokeless stator core structure can reduce the weight and simplify manufacturing process of the motor.The axial permanent magnet synchronous motors are mostly with permanent magnet mounting structures,which quadrature axis and direct axis inductance are approximately equal and the values are very small.Therefore,the vector control of axial permanent magnet synchronous motor is very difficult,and permanent magnet is in the risk of irreversible demagnetization.At the same time,the excessive increase of d-axis current will lead to efficiency reduction and loss increment.First of all,in order to analyze and optimize the new type of motor,the finite element simulation model of YASA motor is established.Because of the YASA motor's special magnetic field distribution,air gap magnetic field direction is from N to S,and perpendicular to the plane of air gap,which cannot use the method of that transform motor magnetic field into the two-dimensional electromagnetic field simulation analysis,just like radial flux motor.This paper will establish a three-dimensional finite element simulation model to analyze the electromagnetic field of the motor.In this paper,it is introduced the characteristics of axial permanent magnet motor with different structure and SMC.And it is analyzed the influence of SMC on the magnetic field distribution of motor,in detail.Then,in order to improve the field-weakening performance of YASA axial motor with surface mounted permanent magnet,this paper puts forward a kind of new combined structure of magnetic pole with permanent magnet and soft magnetic materials,which form the low magnetic reluctance to control flux flexibly.Firstly,a 3D analytical model of motor is established,and back EMF,electromagnetic torque,and flux under different combination.Then simulation analysis based on finite element method is carried out to explore the soft magnetic material's influence on the air gap flux,the simulation results verify the validity of the analytical analysis.Finally,the objective function is established to choose the combination of the soft magnetic part and the permanent magnetic part reasonably,which effectively improves the field-weakening performance YASA motor.