The above studies can be classified according to part of the machine that is studied to modify for reducing the torque ripple and/or the cogging torque.
The torque ripple and/or cogging torque can be reduced by modifying the air gap, the stator and rotor core [1-3].
Furthermore, the second term is called as cogging torque that appears whenever magnet flux travels through a varying reluctance.
The cogging torque due to the reluctance with respect to rotor angle and also first component of the torque in (3) due to the inductance with respect to rotor angle cause undesired torque ripple.
where, [[tau].sub.cog] is the cogging torque, [W.sub.m] is the magnetic energy of the PMSG and [[theta].sub.m] is the mechanical angle of the rotor [6].
The spatial period of the cogging torque, [T.sub.SP], is expressed as below
This value presents same phase waveforms culminate in maximum cogging torque.
The cogging torque can be explained by Fourier series as below
The resultant cogging torque of inner and outer air gap of the DRFPMG depends upon the factors such as slot opening width, the PM pole arc width, and the position of slot openings.
The PM pole arc width plays vital role in the creation of cogging torque.
In this model, the windings present in the stator were removed as they do not play an important role in the determination of cogging torque.
The cogging torque waveform obtained using two-dimensional (2D) magneto static FEA is shown in Figure 4.
Fluctuation curve of cogging torque is shown as function of turning angle of the rotor in Fig.
The presence of uneven rippling of the cogging torque should be noted, maximal value of cogging torque is M = 1.4 Nm.
INFLUENCE OF SLOT OPENING WIDTH ON COGGING TORQUE VALUE
