Study of cogging torque in permanent magnet machines

Cogging torque is produced in a permanent magnet machine by the magnetic attraction between the rotor mounted permanent magnets and the stator. It is an undesired effect that contributes to the machines output ripple, vibration, and noise. This paper analyzes various cogging torque minimization techniques as applied to a permanent magnet machine used in an electric power steering system. A six pole, eighteen slot, surface mounted, rare earth type, brushless permanent magnet machine is analyzed. The resultant cogging torque values are computed using a two dimensional finite element analysis package