Effects of Rotor Asymmetries on d-q Axis Parameters in Synchronous Reluctance Machines

A recent research trend on synchronous reluctance machines (SynRMs) involve devising asymmetric rotor designs, since they promise to reduce torque ripple and improve the overall performance of the machine. This paper analyzes the suitability of estimating the torque output of an asymmetric SynRM by means of traditional torque estimation equations. It is proven that rotor asymmetry introduces a variation in the magnetic axes that is not considered by traditional equations and renders the torque estimation inaccurate. This shift could lead to an imprecise control and estimation of the required torque angle. In this paper, a 4-pole 48-slot single barrier synchronous reluctance machine was employed to investigate this phenomenon by means of finite element analysis. A correction factor is proposed and validated for one-barrier, two-barrier and three-barrier SynRMs.