Modification of Pole Pitch and Pole Arc in Rotor Magnets for Cogging Torque Reduction in BLDC Motor

Abstract

Cogging torque is an unfavorable hindrance in Permanent Magnet Brushless DC (PMBLDC) motor. In medium-low power PMBLDC motors, the surplus oscillations and intolerable noise happen because of the harmonic magnetic forces created by cogging torque. This paper introduces a new approach for the diminution of cogging torque. This method is based on placement irregularities in rotor magnets, and for this a new combination of pole arc and pole pitch was considered. The reference model has a pole pitch of 90° and pole arc of 63°. The new pole pitch is attained by the application of shifting technique on the permanent magnet and for the new pole arc it was resized. An analytical expression using the Virtual Work Method (VWM) Method was derived for locating the pole pitch and pole arc with nominal cogging torque in the PMBLDC motor. The technique is explored using 3D Finite Element Analysis (FEA). The comparison of the simulation and analytical results of cogging torque is accomplished. It is figured out that the cogging torque minimization in the analytical results exhibited acceptable agreement with FEA analysis.

Keywords

• BLDC motor
• cogging torque
• finite element analysis
• virtual work method
• pole pitch and pole arc