The Origin of Permanent Magnet Induced Vibration in Electric Machines

A principal source of vibration in permanent magnet motors and generators is the induced travelling forces from the rotating permanent magnets acting on the stator. The form of the magnetic field and resulting forcing function in the airgap of such machines is critical. The stator is modelled as a solid ring, with no teeth. Various motor parameters were investigated, including the effects of radial versus parallel magnetization, magnetization tolerances, and radial offset. The results were determined with analytical and FEM models. It was concluded that radial magnetization of the permanent magnets was preferable for both vibration and motor performance. Magnetization tolerances and radial offsets yielded a relatively more populated frequency spectrum for the forcing function and thus could lead to a greater probability of resonant modes being excited in the surrounding structure.