Influence of Magnetic Skewing Segmentation on the Cogging and Voltage of a Permanent Magnet Synchronous Generator

Permanent magnet synchronous generator is potential to be used in low-speed wind energy power generation. However, the cogging phenomenon may be undesirable and result in jerking, noise, and vibration during low-speed operation or even a fail to start the generator in high-speed wind condition. The cogging is caused by the varying attraction of magnetic field of permanent magnet at rotor and stator which depends on the rotation angles. The angle skewing of magnetic structure has already been explored to mitigate the cogging phenomenon; however, it presents certain difficulty during the manufacturing process. Step-skewing method is widely proposed as an alternative. This study investigates the effect of the step-skewing on the cogging torque, ripple torque and generated voltage of a permanent magnet synchronous generator. A finite-element method (FEM) based software is used to generate a 3D model and to examine the cases under consideration. Variation of the number of magnetic segments (j) taken are 3, 4, 5, 6, and 7, whereas the variation of the multiplier factor (l) considered are 1, 2, and 3. The analysis on the results of simulation shows that there is a certain value of magnetic-segment number that will result in the best reduction of cogging torque. Higher the number of magnetic segments, lower will be the torque ripple percentage. The generated voltage does not experience any significant increase and tends to remain constant; however, the ripple on the back-EMF voltage wave gets higher when the multiplier factor l increases, causing the waveform to be no longer pure trapezoidal.