Mitigation of cogging torque for brushless interior permanent-magnet motors

In brushless Interior Permanent-Magnet (IPM) motors there exists an oscillatory torque that is induced by the mutual interaction of permanent magnets mounted on the rotor and a slotted structure formed on the stator, generally called the cogging torque. This undesirable torque mainly causes vibration, position inaccuracy and acoustic noise from brushless IPM motors. This paper investigates the in influence of geometric parameters on the cogging torque of brushless IPM motors. An exterior-rotor brushless IPM motor, with embedded magnet poles in a V-shape, is introduced. With the aid of commercial finite-element analysis software, cogging torque waveforms of brushless IPM motors are accurately calculated. The effects of geometric parameters on the cogging torque, including magnet span angle of the rotor, shoe depth and shoe ramp of the stator, dummy slots notched on the stator, depth of the dummy slot and dummy slots notched on both the stator and rotor, are discussed. Ten design cases, with different values of design parameter, are presented to effectively mitigate the cogging torque. Design case X of the brushless IPM motor, with dummy slots on the stator, performs better than the original brushless IPM motor, with a 79.1% decrease in the peak value of the cogging torque. (C) 2015 Sharif University of Technology. All rights reserved.