Performance Prediction of Multiphase Doubly Salient Permanent Magnet Motor Having Nonuniform Air Gap

This paper presents the effects of nonuniformity of the air gap on various performance characteristics of a multiphase doubly salient permanent magnet motor (DSPM). A 6/4 DSPM configuration is analyzed with the help of two-dimensional finite element analysis to predict the effects of three important air gap nonuniformities viz. 1) relative eccentricity between the stator and rotor axes; 2) concentricity error on one half of the rotor; and 3) an elliptical rotor. It is observed that a relative eccentricity up to 20% of air gap has no appreciable effect on the static torque characteristics of the DSPM, above which the permanent magnet torque increases due to reduced air gap, thereby increasing the unbalanced magnetic pull. Therefore, about 20% tolerance in air gap can be allowed for relative eccentricity errors. In case of the concentricity error on one half of the rotor, this tolerance is from -10% to plusmn15% of the air gap, whereas the corresponding limits in the elliptical rotor case are plusmn15% of the air gap