Optimization Research Of Cogging Torque And Slot/Pole Ratio For Permanent Magnet Brushless DC Motor

The brushless motor developed rapidly based on the development of thepower electronics, microelectronic and automatic control system, as well as, thenew permanent magnet material. The brushless motor with fractional slotwinding has many advantages, but still there are a number of inevitable problems.Because of arrangement of fractional slot winding, the motor back EMF andMMF waveform become poor, harmonic content and motor iron loss increase,therefore, the slot/pole combination selection for the brushless motor isparticularly important. The cogging torque can increase the torque ripple, whichleading to vibration and noise and affecting the accuracy of the motor speed andposition control system. Hence, the overall performance of the motor would beaffected. To optimize and analyze the slot/pole combination and the coggingtorque based on motor design in the paper.Firstly, the concept of unit motor and virtual motor are introduced in thepaper. Basis of the star graph, the characteristic and the coefficient of fractional-slot concentrated windings are analyzed and calculated, especially the affectionof the slot/pole combination and the reasonable selection to motor. Forweakening cogging torque, some methods are discussed. A number of differentslot/pole combination brushless motor models are established, also the externalcircuit. The combination of Fourier-decomposition coefficient and finite elementmethod to optimize the cogging torque, include adjusting the slot width, optimizepole arc coefficient, pole segment dislocation, stator teeth auxiliary slot and poleshift, and so on. The advantages and drawbacks of different optimizationmeasures and the principle of parameter selection are analyzed.Finally, a24slot4pole motor cogging torque scheme optimization is presented. The method of optimizing the slot width, selecting the optimal polearc coefficient and the magnetic pole shift are applied totally, with the purpose ofmaintain performance and reduce the cogging torque. After optimizing thecogging torque is greatly weakened and the load performance is improved.