Design of a synchronous reluctance motor using changed symmetry properties of the rotor geometry

Abstract:
Transversally laminated synchronous reluctance machines usually exhibit increased torque ripple, which is problematic with regard to the excitation of mechanical natural frequencies in technical systems as well as the control of the drive itself. The torque ripple can be reduced by skewing the rotor, but this is associated with increased manufacturing costs. In this work, rotor lamination geometries with a reduced number of mirror symmetries are investigated as a possible alternative to skewing. For this purpose, a rotor lamination geometry is first designed as a reference for a given four-pole stator, in which each rotor pole has the same structure. As a result the rotor laminations exhibits mirror symmetries with respect to the rotor fixed d- and q-axes. For comparison, a rotor lamination geometry is designed in which only the rotor poles opposite each other with respect to the axis of rotation have the same structure, so that this rotor geometry only exhibits mirror symmetries with respect to the q-axis. These two rotor lamination geometries are optimized for low torque ripple and compared with each other in terms of their properties. Aspects of series production are taken into account in the design and comparison. Mean torque and torque ripple maps have been simulated for selected laminations of the two rotor lamination variants. Here the rotor geometries which only exhibit mirror symmetries with respect to the q-axis show approximately a halving of the torque ripple at the rated operating point compared with the reference rotor geometries, with a reduction in the mean torque of 1% to 2%.