Effects of Non-Uniform Air-gap on the Performance of Multi-Phase Doubly Salient Permanent Magnet Motors

This paper presents the effect of the non-uniform air-gap on the various characteristics of a 6/4 doubly salient permanent magnet motor (DSPM). Three important cases among the air-gap non-uniformities namely (i) relative eccentricity between stator and rotor axes, (ii) concentricity error on one-half and both halves of the rotor (elliptical rotor) have been analyzed for a 6/4-DSPM using the 2-D finite element (FE) method. It is observed that the poles at the minimum air-gap areas are saturated for eccentricities of 15% and above. At an eccentricity of 95% of the air-gap, the fundamental torque increases from its normal value of 5.15 to 5.86 Nm. The PM torque remains almost the same for the eccentricities up to 5%, and above it the PM torque increases with the eccentricity.