Study Of The Cogging Torque In Permanent Magnet Machines

With the improvement of the properties of permanent magnet material, permanent magne(tPM) machine is more and more widely used to sophisticated control system of speed and position. However, with permanent magnet electric motor, permanent magnet and slot armature iron core interact with each other to produce teeth slot torque, to be specific, the teeth slot torque comes from the tangential force between the rotor permanent magnet and the stator tooth, being the result of the interaction between permanent magnetic pole and the rotor slot, which will exist even there is no current in the rotor. The teeth slot torque may cause pulsation and noise to output torque, which will influence the position control system and speed control system, especially the function and accuracy of the low-speed system. The teeth slot torque influences electric motor's low-speed performance in the speed control system and the high-speed performance and accuracy in the position control system. Tile synchronous magnetization magnetic pole is the most widely used on permanent DC electric motor, surface permanent synchronous electric motor and brushless DC motor.In this paper, the methods of weakening the cogging torque of permanent synchronous electric motor are categorized into three types, i.e., changing the parameters of permanent magnetic pole and the parameters of armature and choosing reasonable number of armature slots and poles. And specific methods of weakening cogging torque are also illustrated here. The author employs the software Magnet to calculate the cogging torque of a 4-pole 24-slot permanent synchronous electric motor. The several methods of weakening cogging torque, including tilted slot, tilted pole, magnetic pole excursion and optimized polar arc and auxiliary slot, are analyzed in different motor structures. The results coincide with those worked out with numeric values adopted in other articles. In actual project, either one or more than one weakening methods can be used according to the situation. Though teeth slot torque cannot be completely eliminated, we can make it acceptable with reasonable methods.