An acoustic model for a permanent magnet machine: modal shapes and magnetic forces

A modal analysis concept for calculating the vibrational level of an electrical machine stator is presented. Using this concept, the designer is freed from calculating real magnet forces, which is normally difficult and inaccurate. Only flux linkages have to be calculated which can be easily done using finite element methods and the vector potential as the unknown function. Furthermore, the energy method also deals with any random or tangential movement of the stator surface. The main disadvantage is the need to know the mode shapes accurately. These can only be measured with great effort in the low-frequency region (up to 1 kHz). In the higher frequency regions, hundreds of modes exist, although, at this point, other approximations can be made.<>