Design techniques for reducing the cogging torque in surface-mounted PM motors

Several techniques may be adopted in motor design of surface-mounted permanent magnet motors in order to reduce the cogging torque. This paper describes the various techniques, (both classical and innovative techniques), giving for each of them a theoretical justification. To this aim, a simple original model of the cogging torque mechanism and a Fourier analysis are introduced. As a result, it is highlighted that some techniques are not always utilizable, and some of the well known ones may be even depreciatory when not used correctly. In addition, effects on back EMF are discussed.