Five methods of stator natural frequency determination: Case of induction and switched reluctance machines

In this paper, in order to predict magnetic acoustic noise emitted by electrical machines, five methods used to determine machine natural frequencies are presented and compared considering elementary structures such as smooth cylinders. Then, the cases of toothed rings such as induction and switched reluctance machine stators are taken into account, leading finally to consider these complete machines. The different methods can be divided into three sets. The first one is analytical and considers Jordan laws and suggested extension. The second one uses a finite element software. The three other methods are experimental and make use of an impact hammer, a shaker and the magnetic excitation technique.