Minimization of torque pulsations in a trapezoidal back-EMF permanent magnet brushless DC motor

This paper discusses the different methods used to reduce the torque pulsations (i.e. cogging torque and torque ripple) in a trapezoidal back-EMF permanent magnet (PM) brushless DC motor. The paper covers the design options to reduce both cogging torque and torque ripple. The effect of stator ampere-turns, the influence of rotor magnetization and the effect of the processing of electrical steel used in the fabrication of the stator on the motor torque ripple are discussed. The conclusions in the paper are supported by experimental results. A 3-phase, 18-slot, 6-pole brushless DC motor using high energy NdFeB magnets is used to illustrate the findings