The distribution of magnetic flux density [1-3,6-7,21] and the variation in magnetic energy [13-14,16-19] is used to reveal the formation of torque ripple or the cogging torque.
There are special magnet positions according to a slot-tooth pair, when the cogging torque is taken into account (Fig.
Meanwhile, the cogging torque takes the maximum value and then becomes zero (position 3 and 7).
The cogging torque of the rotor without the pole shifting is high, due to the fact that it has all harmonics of the cogging torque.
The setup of the cogging torque measurement system of the designed and manufactured PMSG is given in Fig.
The cogging torque of the PMSG with two different designed rotors without and with the pole shifting has been measured by the Crane Electronics UTA-451-0020-0P 5 Nm brand/model transmitter.
Now the cogging torque waveforms of inner and outer air gaps were different.
In conventional PM generators, the cogging torque is reduced if the permanent magnet width is almost equal to an integer number of slot pitches.
The cogging torque values obtained before and after changing the magnet pole arc width are given in Table 1.
The most effective way to reduce cogging torque is skewing of stator slots or rotor poles.
Further we will consider possibilities to reduce pulsations of cogging torque by skewing of stator slots, if slot opening width is equal to interpolar distance ([b.sub.s] = [b.sub.w]).
If equality [b.sub.m] = [b.sub.z2] does not exist, the flux through the stator tooth increases, value of maximal cogging torque increases also, so you should choose magnet width equal to rotor teeth width.