| Compared to bearing motors,the bearingless permanent magnet synchronous motor(BPMSM)has the advantages of frictionless,high speed,durability,and no lubrication.Compared with the use of magnetic bearing motor,the axial length of the motor can be sharply shortened,the volume of the motor can be reduced and the range of the application can be expanded.However,there are two sets of windings embedded in the stator slot of the BPMSM,a set of torque winding and a set of suspension winding.The rotor is subjected to both the radial suspension force and tangential torque force.Therefore,it is of great significance to conduct in-depth research on the suspension mechanism of the bearingless permanent magnet synchronous motor,the selection of electromagnetic parameters and the electromagnetic characteristics.Aiming at the unique winding arrangement characteristics of the bearingless permanent magnet synchronous motor,the suspension mechanism and operation characteristics of the bearingless motor are systematically analyzed,and the relationship between the pole numbers of the torque winding and the suspension winding are given when the motor obtains a stable radial suspension force.Based on the Maxwell tensor method and the virtual displacement method,the BPMSM levitation force and electromagnetic torque analytical models are established,and the effects of the winding excitation on the radial levitation force and the tangential torque force are discussed.Aiming at the problems of magnetic field coupling,high magnetic density and easy demagnetization of permanent magnets in the electromagnetic design of bearingless permanent magnet synchronous motors,the influence of the structural parameters of the permanent magnets on the air-gap magnetic density and the levitation force was discussed,and the rotor permanent magnets’ easy demagnetization region are also analyzed.,the maximum winding excitation current is derived considering the demagnetization effect.The characteristics of electromagnetic parameter design of bearingless permanent magnet synchronous motor are summarized,and the electromagnetic parameter design of the motor is completed.Finally,through the study of the established two-dimensional finite element model of the motor,the influence of the torque magnetic field and the suspension magnetic field on the air-gap flux density is analyzed,the law of the suspension force and the excitation amplitude is revealed,and the accuracy of the mathematical model of the suspension force is verified.Aiming at the change of electromagnetic characteristics when the rotor of bearingless permanent magnet synchronous motor is eccentric,a finite element model considering rotor eccentricity is established,the dynamic electromagnetic force calculation formula is deduced.The distribution law of the dynamic electromagnetic force at the rotor surface,stator tooth tip and tooth wall before and after eccentricity is clarified.By analyzing the spatiotemporal characteristics of radial electromagnetic force,the accuracy of dynamic electromagnetic force calculation is indirectly verified.The effects of unbalanced magnetic forces due to radial suspension forces and eccentricities on motor electromagnetic vibrations were studied in combination with the calculated results of the pre-and post-eccentricity radial electromagnetic forces of the stator teeth.In this article,the calculation methods and vibration conclusions involved in the studied BPMSM electromagnetic vibration can provide reference for the analysis of the same type of motor. |
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