| Compared with conventional axial flux permanent magnet synchronous motor(AFPMSM),ironless AFPMSM is suitable for applications with limited axial space and higher requirements on power density or torque density due to its characteristics of eliminating cogging torque,prominent overload capacity and high efficiency.However,the absence of the stator core has also brought some problems:on the one hand,the equivalent air gap length of the motor is increased,which leads to the reduction of air gap magnetic density.Therefore,the rotor structure needs to be designed reasonably.On the other hand,because the alternating magnetic field directly acts on the windings,eddy current loss is one of the main losses of this type of motor,which affects motor performance and efficiency.Therefore,accurate calculation and suppression of eddy current loss of windings are of significant to the design of ironless AFPMSM.According to the characteristics of ironless AFPMSM,based on the application background of special vehicles using in-wheel motor drive technology,this paper implements research on aspects including the electromagnetic design,winding loss characteristics and calculation method of ironless AFPMSM.The main research contents include the following aspects:Firstly,the influence of the selection of number of disks,the structure of stator and rotor and the selection of slot/pole combination on the performance of ironless AFPMSM is studied.The multi-disk structure with two stators and three rotors is adopted in this research.The influence of winding arrangement on inner diameter embedding is studied.The general method of Litz wire parameter selection is given from the perspective of space utilization.The general principles of ironless AFPMSM electromagnetic design are summarized.According to the performance requirements of special in-wheel motors,the basic electromagnetic design scheme of ironless AFPMSM is obtained.Secondly,in order to meet the requirements of high power density and high efficiency of the motor,the rotor structure is optimized.To improve the no-load back-EMF amplitude and sinusoidality for optimization purposes,the optimization design is carried out from two aspects: permanent magnet and rotor support structure.The three-dimensional distribution characteristics of air gap magnetic field of magnetic pole combined ironless AFPMSM are studied,and the distribution laws of different components of air gap magnetic density are obtained.Therefore,the design scheme of the magnetic pole combination type ironless AFPMSM is obtained,and the electromagnetic performance is compared with the traditional magnetized structure motor.Thirdly,according to the main causes of winding loss of ironless AFPMSM,theinfluence of Litz wire parameters on winding eddy current loss is studied,and the selection principle of diameter is given from loss aspect.Accounting for the influence of end effect,an analytical model of no-load air gap magnetic field of ironless AFPMSM is established by using split-loop equivalent linear motor method,which improves the calculation accuracy of air gap magnetic density component.Based on this,the eddy current loss of the winding is calculated by the calculation formula of circular conductor,and obtains its distribution characteristics.Finally,a 3-D finite element modeling method using single conductor equivalent multi-stranded Litz wire is proposed.The influence of different mesh lengths on the solution accuracy is studied.The selection and conversion method of the equivalent wire diameter of the winding are studied,and the distribution characteristics and proportion of the eddy current loss of conductors in different parts of the winding are analyzed.Through the comparative analysis of the results of the 3-D finite element and the analytical method,the rationality and feasibility of the solution method are verified. |
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