Investigation of the segment order in step-skewed synchronous machines on noise and vibration

This paper deals with the noise radiated by step-skewed permanent magnet excited synchronous machines and the particular influence of the segment order on the vibro-acoustic behavior. It is well known that the shape of the electromagnetic forces acting along the circumference of the stator core is decisive for the generation of noise and vibration. The influence of the axial behavior of these forces is, however, to a great extend unexplored. A first insight is gained in this paper by means of a structural dynamic response analysis of a stator for different skewing sequences. Each sequence excites a particular combination of structural modes differing in their axial behavior. Structural modes of a low axial order have shown to be significantly more relevant concerning the acoustic behavior of a machine. Therefore, an analytic method is developed that allows a comparison of different skewing arrangements regarding the excitation axial modes without the necessity of structural FE simulations. A comparison of three particular skewing arrangements (linear, v-shaped, and zigzag predicts a significant influence on the vibro-acoustic behavior. To validate the results, three prototype traction machines have been built. The measurement results follow the predicted influence with differences in the sound pressure level of more than 10dB.