Analysis of harmonic field effects in reluctance synchronous machines

Abstract

The reluctance synchronous machine (RSM) is a type of synchronous machine which has no windings in the rotor and can be referred to as a non-excited synchronous machine. The RSM can be classified as either single or double salient machine. The single salient machine refers to saliency in the rotor only and double saliency refers to saliency in the rotor and stator. The RSM is based on the principle of reluctance, were torque is produced due to different reluctance paths within the rotor of the machine. The term reluctance is referred to the resistance of a material towards the flow of magnetic field. Since the invention of vector controlled drives, RSMs regained the popularity of researchers and are becoming a field of interest. The RSM have numerous advantages, besides being cheap, robust, and reliable, the stator part is exactly the same as an induction machine. This will enable easy and cost efficient upgrades. Furthermore due to the non existing rotor currents heat dissipation will be low. However the RSM has an inherently high torque ripple due to its rotor geometry. The torque ripple is defined as the difference between maximum and minimum deviation of the torque referred to the average torque. The torque ripple creates uneven pull on the rotor which creates deformation of the rotor and consequently uneven run. As a result the torque ripple indicates that the speed of the RSM changes permanently. The machines designers ultimate goal would be to design a machine with the lowest torque ripple combined with a maximum average torque. The aim of this thesis is to provide a detailed analysis on the field quantities and its harmonics of a RSM and to examine the effects which these harmonics have on the torque production. This analysis would give designers a better understanding of the principles of RSMs and help to obtain certain performance results. The research design and methodology will include the harmonic content of the flux density components in the center of the air gap. The flux density components will be analysed in terms of its harmonics and the torque produced by these flux density harmonics will also be investigated.