Vibration reduction in electric machine by interlocking of the magnets

A principal source of vibration in permanent magnet (PM) motors and generators is the traveling attractive forces from the rotating permanent magnets acting on the stator. To reduce the vibration, it is necessary to modify the vibration source and the system characteristics. This vibration source and its reduction were investigated by the finite-element method (FEM), the Maxwell stress tensor, and Fourier decomposition. To avoid coincidence with structural resonances of the machine, it is desirable to reduce both the number of frequency components of the magnetic force and their amplitudes. Interlocking of the magnets, by changing the magnet geometry and including the higher energy magnet materials at the pole transitions, is proposed to reduce the contribution of driving frequencies. Interlocked higher-energy PMs play a favorable role in reducing the overall variation of the magnetic force by compensating the sudden change of the magnetic force at the pole transitions without affecting the torque