Effect of lamination asymmetries on magnetic vibrations and acoustic noise in synchronous machines

This paper analyses the effect of stator or rotor lamination asymmetries (non-circularities) on magnetic vibrations and acoustic noise radiated by electrical machines, and more especially by permanent magnet synchronous machines. A theoretical analysis is first carried based on permeance / magnetomotive force model. Then, some full electromagnetic and vibroacoustic simulations are run at variable speed using analytical models to validate analytical understandings. It is shown that lamination asymmetries, and in particular the number of periodic non-circularities, can significantly increase noise and vibrations levels due to Maxwell forces. The number of segments, weldings or stiffeners should be multiple of the number of pole pairs to minimize the appearance of additional resonances due to new force wavenumbers. Some conclusions can apply to other magnetic asymmetries involved in modular stators and uneven magnetization PM rotor.