Analysis and minimization of torque ripple for variable flux reluctance machines

Abstract

Variable flux reluctance machines (VFRMs) are permanent-magnet-free three-phase machines and are promising candidates for applications requiring low cost and robustness. This paper studies the torque ripple and minimization methods for 12-stator VFRMs. Starting with the analysis of harmonics in the self and mutual inductances of field and armature windings, instantaneous torque equations are derived by virtual work method, which give a clear view on the dominated torque ripple components in VFRMs. Afterwards, the influences of motor topology on harmonics of the inductances as well as the torque ripple are investigated, such as number of rotor poles and tooth arc, etc. On the basis of the aforementioned analysis, harmonic injections in field current and armature current are analyzed for torque ripple reduction. The effectiveness of these two methods is investigated for non-saturated and saturated 12/10 VFRMs based on 2D finite element analysis. The results show good performance of torque ripple minimization by harmonic armature current injection.