Study On Permanent Magnet Torque Motors With Low Torque Ripple

Permanent magnet torque motor is a kind of permanent magnet synchronous motor with low speed,high torque density,strong and overload capacity,precision positioning that is capable of driving a load directly and rigidly.With the improvement on permanent magnetic materials and the development of power electronics and control theory,permanent magnet torque motors have received more and more attention and applications.However,the torque ripple of the permanent magnet torque motor has impacted on positioning and vibration of motion systems,especially on fast setting.To solve this problem,this paper mainly studies a Bread-loaf magnetic pole structure.Through the design,analysis and optimization,the low torque ripple of the permanent magnet torque motor is obtained.First of all,the basic principle of the permanent magnet torque motor,electromagnetic design and magnetic field analysis method were briefly introduced.The mechanism of the torque ripple of the permanent magnet torque motor was analyzed and discussed in detail.Methods for suppressing torque ripple of a permanent magnet torque motor was introduced at the same time.Secondly,this paper analyzed the no-load air gap magnetic field of permanent magnet torque motor with the Bread-loaf magnets.The method of separating variables was used to analyze the no-load air-gap magnetic field of the slotless permanent magnet torque motor with Bread-loaf magnets in firstly.Then,the cogging effect was considered using the method of conformal mapping.The correctness was verified by finite element method.The influence of related parameters was analyzed in detail.It shown that the sinusoidal shape of the air gap magnetic field waveform generated by the poles of this type of structure was better.Then,the cogging torque was analytically calculated by Maxwell tensor method.The influence of related parameters on the cogging torque was analyzed.Genetic algorithm was used to optimize the cogging torque.It was significantly reduced after optimization.Finally,a permanent magnet torque motor with a Bread-loaf magnetic pole structure for robot joints was designed based on the above analysis.The electromagnetic design process was introduced in detail.The electromagnetic performance and torque ripple of the motor were analyzed and designed using the method proposed in this paper,and the prototype was prototyped.The hysteresis dynamometer was used to test the working characteristics and the cogging torque.The results shown that the torque ripple is significantly reduced which is coincident with the methods promoted in this thesis.