Analysis of torque in permanent magnet synchronous motors with fractional slot windings

The influence of various types of windings on the cogging torque and the total torque developed by a three-phase permanent magnet synchronous motor (PMSM) is investigated. The number of poles and rotor geometry are fixed and the stator slot number is modified. The finite element technique is used for the computation of the machine characteristic. The torque is determined by means of the Maxwell stress method. It is shown that the optimizing the cogging torque to a low value is therefore not sufficient to obtain a low torque ripple.

I. Introduction

Permanent magnet synchronous motors (PMSM) are widely used in many industrial applications for their compactness, highly efficient and high torque density. As their cost continues to decrease they have the opportunity to become a dominant force in the industrial applications market.