Radial force calculation and acoustic noise prediction in switched reluctance machines

The paper presents an analytical method for calculating the radial force and predicting the acoustic noise in switched reluctance machines. The main source of acoustic noise in an SRM is the radial magnetic force inducing resonant vibration with circumferential mode-shapes of the stator. An analytical relationship between radial force and radial vibration is determined, which can be used to predict the noise power level at the frequency of operation. The vibration and sound are functions of machine dimensions, material properties and rotational speed. The knowledge of the circumferential mode-shapes of vibration, the natural mode-frequencies of the stator and the frequency spectrum of the radial magnetic force can be effectively utilized to design SRMs with minimal noise through geometrical design variations. The effect of the number of stator and rotor poles on acoustic noise can also be analyzed with the model presented in this paper. Magneto-dynamic simulation by finite element software is also carried out to verify the calculation of radial force using the proposed analytical model.