Research On Torque Ripple Reduction Method Of Permanent Magnet AC Servo Motor

With the advancement of science and technology and the enhancement of the level of industrial modernization, the accuracy of servo control system have become increasingly demanding. Torque ripple is concerned as an important performance parameter in servo control system and it directly affect on control precision of servo system. Because of torque ripple, vibration is generated when low speed and noise is generated when high speed. At present, minimization techniques of torque ripple of servo motor are extensively concerned, and the method of reducing cogging torque is paid more attention. In this paper, minimization techniques of cogging torque of servo motor are researched, and the effects of auxiliary slot and rotor eccentricity on cogging torque are mainly researched.Firstly, by using Ansoft Maxwell, auxiliary slot on the top of stator teeth is researched to reduce cogging torque. Several permanent magnet motor models are founded, and waveforms of cogging torque are obtained with different sizes of auxiliary slots. By analyzing, the effects of the size of auxiliary slots on cogging torque are analyzed and the optimal size is obtained. Moreover, the effect of auxiliary slots on back-EMF is also analyzed.Secondly, the analytical expression of cogging torque is derived based on energy method with considering the size of auxiliary slots. The calculation program is written by using Matlab software, and then several motor models are calculated. The effects of the size of auxiliary slots on cogging torque are analyzed and the optimal size is determined. The conclusion obtained by analytical method is almost identical to the finite element method. Moreover, the scope of application of auxiliary slot on the top of stator teeth is obtained.Thirdly, by using the software of Ansoft Maxwell, the effects of rotor static eccentricity, rotor dynamic eccentricity and the position of minimum air-gap on cogging torque are analyzed.Finally, permanent magnet AC servo motor is designed, and auxiliary slot on the top of stator teeth is adopted to reduce cogging torque. The prototype is manufactured, and then the conclusions which are obtained by Finite element method and analytic method are verified by test. In addition, performance parameters of the prototype meet the design requirements well.