Analysis of cogging torque in surface-mounted permanent magnet machines with segmented stators

Electrical machines with high power density and small packaging size are desirable for many industrial and commercial applications. It is often preferable to employ a segmented stator, since the topology facilitates a high filling factor of the windings. In the common individual segmented stators, there exist too many additional air gaps which lead to the decrease of the back electromotive force (EMF) and may cause the difficulty of manufacture. This paper proposes several feasible stator segmentations with uniform stator segments or nonuniform stator segments. Influence of the additional gaps on both the magnetic field symmetry and the cogging torque is investigated. It is found that the presence of these gaps increase the cogging torque magnitude and period due to the magnetic field asymmetry, while different amount and location of the gaps can cause various increase in the amplitude of cogging torque waveform.