Design And Analysis Of Modulated Magnetic Poles In Bearingless Permanent Magnet Synchronous Moto

The stator of bearingless permanent magnet synchronous motor(BPMSM)usually has two sets of winding named torque winding and suspension force winding.When the suspension winding is given appropriate current,motor air-gap magnetic field distribution will contain the bias component,which generate the rotor suspension force that avoid the problem of shortening life due to the fraction of traditional mechanical bearing when it comes to high speed application,which reduce the operational costs of the motor.It has been widely used in vacuum and ultra-clean special transmission occasions.The process of motor rotation depends on suspension force to suspend the rotor with no mechanical bearing support,so it is necessary to ensure the stability of the motor torque and suspension force.In this paper,the structure of modulated magnetic pole is proposed and the parameters are designed for surface-mounted BPMSM based on the fine calculation of magnetic field.Firstly,the expression of magnetization of rotor pole and the stator winding current density are deduced in view of BPMSM,the magnetic field analytical model is set up by using sub-domain model method.The magnetic field solution region of the motor is divided into rotor region,air gap region and stator region and the magnetic field of the motor is solved by establishing magnetic field constraint equations and boundary conditions between the regions.The torque and suspension force of the BPMSM are calculated at the same time.The analytical model can be applied to the surface mounted BPMSM with arbitrary magnetic pole parameters,which provides a new idea for the design and optimization of surface mounted BPMSM.The suspension force and torque of BPMSM are closely related to the magnetic force distribution(MMF)of rotor,which is related to the magnetic pole structure parameters.the harmonic order of the rotor MMF.which cause torque and suspension force fluctuation are determined based on the stator and rotor MMF analysis.The design method of modulate magnetic pole based on the specific harmonic elimination(SHE)method is proposed.and the parameters of the modulated magnetic pole are precisely solved based on the established magnetic field analytical model.The result shows that the motor with magnetic pole designed based on the SHE method can effectively eliminate specific rotor MMF harmonic and reduce the corresponding order torque and levitation force fluctuation,which improves the stability of motor.An unequal amplitude permanent magnet width modulation method,that is,carrier waves with different amplitudes are used to modulate the modulate wave is proposed for BPMSM.On the one hand,this method can solve the problem of small adjustment range of the polar arc coefficient of the traditional equal amplitude permanent magnet width modulation.On the other hand,it can avoid the phenomenon that the torque fluctuation suppression effect is weakened when the gap between permanent magnets is too large due to the modulation ratio is too small.Based on Taguchi method,the magnetic pole optimization design of BPMSM is realized with the minimum fluctuation of torque and suspension force as the optimization objective,the output performance of the motor and the rationality of magnetic pole parameters as constrains,and the magnetic pole structure parameters of unequal modulation as optimization variables.The best parameter combination of the unequal amplitude modulation permanent magnet is achieved.The structure of the whole magnetic pole,the structure of the equal amplitude modulated magnetic pole and the structure of the unequal amplitude modulation magnetic pole are compared and analyzed by finite element method.The results show that the fluctuation of torque and suspension force of BPMSM can be effectively reduced by optimizing the structure parameters of the magnetic pole with unequal amplitude modulation,and the effectiveness of the proposed method is verified.