Synthesis of cogging torque in permanent magnet machines by superposition

The paper investigates the calculation of cogging torque in permanent magnet machines by the superposition method, the resultant torque being synthesized from the torque components when is associated with a single stator slot or a single rotor magnet. It is shown that the resultant cogging torque can only be reliably synthesized from the cogging torque associated with a single magnet when the magnet pole-arc to pole-pitch ratio is significantly less than 1, while, in general, the resultant cogging torque can be synthesized to a high accuracy from the single slot component. The superposition technique is applied to motors having a fractional number of slots per pole.