Computation and measurement of magnetically induced vibrations of a switched reluctance machine

The computation of magnetically induced vibrations within an electrical machine is a task that presents certain difficulties. Yet, the results of such a computation will be of utmost importance in the magnetic and vibratory design of a machine as well as of its power supply. Since the damping term of a machine assembled on a workbench is practically impossible to predict, as are the sizeable number of coupled phenomena that cause vibrations, there is in essence no accurate theoretical model able to compute vibrations during the initial design stages of the machine. Moreover, a model that is complete, yet cumbersome to implement, does not in general enable the type of parametric studies necessary for developing a complex machine-converter set to be carried out. In the paper, therefore, the authors have not only adopted some simplifying hypotheses, but also have combined both theoretical and experimental results to construct such a model. The model consists of a mechanical unit which represents the machine modal characteristics and allows, in particular, development of a transfer function between the magnetic forces and the stator vibrations. These forces are of a global order of magnitude and have been computed with the help of a second magnetic unit for which it has been assumed that the distribution of stresses exerts no influence whatsoever on the acceleration at the stator periphery. A final electrical unit makes it possible for us to compute the current present in the phase. The validity of this model is then verified experimentally, and an application example is provided.