Vibroacoustic Prediction and Mechanism Analysis of Claw Pole Alternators

A multiphysics simulation model that consists of electromagnetic field, mechanical field, and acoustic field was established to predict the electromagnetic vibration and noise of claw pole alternators. First, magnetic force exerted on the stator inner surface was calculated by three-dimensional (3-D) transient electromagnetic field analysis and the characteristic of magnetic force was analyzed. Second, finite-element modal analysis of alternator assembly was conducted while taking into account the anisotropy of the stator core and armature winding and the installation condition. Simulation result was validated by modal test. Afterward, magnetic force was transferred to the structural mesh using mesh mapping method and the vibration and noise were predicted by using mode superposition method and boundary-element method, respectively. Simulation results agree well with those measured by experiments. Finally, the mechanism of electromagnetic vibration and noise of the claw pole alternator was revealed with the help of 2-D Fourier transform of magnetic force and the mode participation factor of each mode. Results show that for three-phase 12-pole/36-slot claw pole alternator, electromagnetic vibration, and noise are mainly caused by the zeroth-order (circumferential spatial order) force harmonics whose frequencies are 36kf(r) (k = 1, 2, 3, ...) and the sixth-order (circumferential spatial order) force harmonics whose frequencies are (36k +/- 6) f(r) (k = 1, 2, 3, ...).