Influence factor analysis of PMSM air gap flux density

PMSM (permanent magnet synchronous machine) has high efficiency and torque. The influence of the air gap flux density on torque and induced EMF is proverbial, thus it is very important to discuss influence factor of PMSM air gap flux density. In relative literatures, however, it has not been reported. This paper analyze the relative factor of influence air gap flux density, and compare SPM (surface mounted permanent magnet) with IPM (interior permanent magnet) machine, then presents applied and intelligible conclusions: the machines air gap flux density is changed with the air gap length varies, the air gap flux density variety of IPM machine is bigger than that one of SPM. To IPM, using non-magnetism shaft is our advice. To SPM, in order to ease fabricate, we suggest use magnetism shaft. To IPM, small pole arc coefficient is suitable; To SPM, however, more bigger pole arc coefficient is necessary. To IPM, the air gap flux density has a suitable value due to the restriction condition of rare earth magnet thickness. To SPM, the restriction condition of rare earth magnet thickness is not existence, the air gap flux density is enhanced with the increase of the rare earth magnet thickness, then it reaches a constant when the rare earth magnet thickness exceed some extent; IPM synchronous machine bears "flux concentration function", when its pole pairs is more than or equal to 3, B_δ/B_M > 1 or 4, B_δ/B_r > 1. To SPM, it has no "flux concentration function".