Calculation and measurement of eigenmodes for a canned switched reluctance machine

A great disadvantage of switched reluctance machines is the heavy noise emitation, caused by the radial forces in the airgap, which excite the structure to vibrate. Especially the stator vibrations produce heavy noise, when the frequencies of the excited forces correspond to the eigenfrequencies of the stator. Every structure has its characterizing eigenfrequency and the corresponding shape of deformation, the eigenmode. For the development process of an electrical machine design it is important to know both. Not all eigenmodes will be excited by the radial forces due to the excitation of the windings. There are different methods to derive the eigenfrequencies and eigenmodes. The value of the frequencies can either roughly be estimated with analytical models for simple structures or determined with finite-element simulation (FEM) and validated with measurements. In this paper different analytical models are presented and compared with numerical solution and measurements.