| Bearingless permanent magnet synchronous motor(BPMSM)is a new type of motor combining magnetic bearing technology with permanent magnet synchronous motor technology,which has the advantages of frictionless,no lubrication,long life,high efficiency,etc.It has a broad application prospect of engineering in life science,flywheel energy storage and aerospace and other fields.In order to achieve active suspension of the motor,both torque winding and suspension winding are embedded in the stator slot of the bearingless permanent magnet synchronous motor.With the introduction of the suspension winding,the thermal load of the motor is increased,and the risk of the winding insulation damage and short-circuit fault is increased,which has a negative impact on the operational stability of the motor.In addition,the torque magnetic field and the suspension magnetic field have the same flux path,resulting in an increased coupling of the two types of magnetic fields in the air gap and an increase in the harmonic content of the air gap magnetic field,which further affects the reliable operation of the motor.Therefore,the paper analyzes the operational performance of bearingless permanent magnet synchronous motors.The working principle,mathematical model,coupling relationship of the spatial-temporal multi-harmonic magnetic fields,dual winding design and rotor structure optimization are studied by using finite element method and analytical method.Firstly,an 8.5k W bearingless permanent magnet synchronous motor is studied in this paper,and a 2D transient field analysis model of the prototype is established using the timestepping finite element method,and the mechanism of the radial suspension force of the bearingless permanent magnet synchronous motor is studied.On this basis,combined with the magnetic field distribution characteristics under the coupling effect of dual windings,the frequency domain distribution of the air-gap multi-harmonic magnetic field is obtained by using the fast Fourier analysis,and the influence relationship between electromagnetic torque and radial suspension force is determined,which provides reference for the establishment of mathematical analysis model of bearingless permanent magnet synchronous motor.Secondly,the characteristics of the air-gap multi-harmonic magnetic field distribution of the bearingless permanent magnet synchronous motor are studied by using the magnetomotive force-permeability method.And the mathematical expressions of the constant and fluctuating components of the suspension force under the coupling effect of the multiharmonic magnetic field are also derived by using the Maxwell stress tensor method.On this basis,combining the spatial distribution and temporal variation of the magnetic field,the influence mechanism of the coupling effect of the magnetic field on the radial suspension force is analyzed,and the key magnetic field parameters affecting the variation of the motor performance are determined,which provides the theoretical basis for the suspension control design and the optimization of the motor structure of the bearingless permanent magnet synchronous motor.Then,by combining the analytical method,the expressions of electromagnetic torque and radial suspension force under the constraints of slot space area of dual winding,electromagnetic load and thermal load are derived by the analytical method,and the correspondence between electromagnetic torque and radial suspension force is determined.The time-stepping finite element analysis method is also used to study the variation of electromagnetic torque and radial suspension force with the winding current,and the coupling relationship between electromagnetic torque and radial suspension force is analyzed with the same winding area allocation of the stator slot space of dual winding,and the limit variations of the torque characteristics and suspension performance under the thermal load constraint are obtained.On this basis,the optimal matching relationship between the electromagnetic torque and the radial suspension force under different ratio coefficients of slot space winding area of the dual windings is determined,which provides a reference for the stator winding design of the bearingless permanent magnet synchronous motor.Additionally,based on the rotor structure and magnetic field distribution characteristics of bearingless permanent magnet synchronous motor,the mathematical expression of permanent magnet magnetomotive force of bearingless permanent magnet synchronous motor is modified by analytical method,and the influence of rotor structure parameters on electromagnetic torque and radial suspension force is determined.Combined with the finite element method,the distribution of harmonic content in the air gap magnetic field corresponding to different magnetization directions,pole arc coefficients,and pole eccentricity of the permanent magnet is obtained.The influence of the permanent magnet structure on the electromagnetic characteristics and suspension performance is revealed,and the optimal design for the rotor permanent magnet of the bearingless permanent magnet synchronous motor is determined.The research results can provide the reference for the optimal design of the bearingless permanent magnet synchronous motor.Finally,in order to verify the correctness of the analytical model and the optimized design results of the bearingless permanent magnet synchronous motor,a prototype is made by combining the design parameters of the bearingless permanent magnet synchronous motor,and an experimental test platform is built to test the electromagnetic and suspension performance of the prototype.and the results are compared and analyzed with the results of finite element analysis and analytical methods. |
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