Influence of Material and Geometrical Properties of Permanent Magnets on Cogging Torque of BLDC

Abstract

Aim of this study is to investigate the influence of both material and geometrical properties of surface mounted permanent magnets (PM) on cogging torque of a brushless DC motor (BLDC) by means of numerical modeling based on finite element method (FEM). To this end, a 2D numerical model of the BLDC motor is built by using the software package Ansys Maxwell. In this study, we analyze the machine properties in no excitation mode (i.e. no stator current is applied) and calculate the distribution of magnetic flux density within the entire motor, the magnetic flux density in the air gap, the cogging torque and the back electromotor force (EMF). Firstly, analysis is performed for four different magnets. It is seen that while cogging torque, back EMF, and magnetic flux density in the air gap for the strongest magnet material have the highest values, the lowest values of these are obtained for the weakest magnet. In the second part of the study, the effect of variation of magnet geometry on the cogging torque, magnetic field density and back EMF of BLDC is examined. Three magnet embrace values are handled in this study. When the magnet embrace increases, the value of the cogging torque reduces. Besides, the maximum values of the back EMF are approximately the same for different magnet embraces, while shapes of the back EMF only change based on the magnet embrace. According to the results, the cogging torque strongly depends on the material and geometrical properties of the magnets.