Analysis of Electromagnetic Force Ripple on the Rotor of a Bearingless Synchronous Reluctance Motor

This paper presents the analysis of electromagnetic forces on the rotor of a synchronous reluctance motor under self-levitation operation. Due to the presence of flux barriers, the ripple content in the torque and levitation force brings a major concern. Different schemes of torque ripple reduction have been taken as a reference and their effects on the levitation forces are investigated. The paper explores the advantages and disadvantages of rotor skewing, stator winding chording and asymmetric flux barrier design on the levitation forces. Finite element analysis has been used with current source, and the computations are performed by the angular sweep of the rotor varying with time. Skewing helps to damp the slot harmonic when the rotor is skewed for one slot pitch. Multi-slice model has been used to determine the skewing effect. A significant improvement in the reduction of levitation force ripple has been observed when the rotor is skewed. The chording slightly reduces the levitation force ripple. The asymmetric flux barrier design shows improvement in the reduction of torque ripple, however the levitation force has additional harmonics due to the asymmetry which is not a good option when used for the bearingless motor operation.