Comparative Study of Air-Gap Field Distribution Characteristics Among Different Pole Array in SPM

Abstract

The pole array directly influences air-gap filed distribution and hence output torque performance especially in surface-mounted PM machine (SPM). The fundamental wave of air-gap magnetic flux density determines the average torque, and harmonic generates torque ripple. In generally, there is a trade-off between them. To simultaneously obtain high torque and low torque ripple, the selection of pole array and corresponding design parameters is essential for PM machine design. Thus, the air-gap field distribution characteristics of three kinds of pole arrays, i.e., radial-magnetized, tangential-magnetized and Halbach array are analysed and compared by finite element analysis (FEA). The effects of the pole arc coefficient and PM thickness coefficient on air-gap field distribution are analysed by fast Fourier transform (FFT). It indicates that the effects of the pole arc length on the harmonic component of air gap magnetic field is obvious and the effects of the pole thickness is very little. The performances of three pole arrays under different pole thicknesses are compared. The results show that radial-magnetized pole array perform better than Halbach array and tangentialmagnetized pole array on fundamental flux density when thickness of magnetic pole is small. Besides, when the thickness of magnetic pole exceeds 0.9 times of pole distance, tangential-magnetized pole array can obtain higher fundamental magnetic density than Halbach array.