Characteristics analysis of electromagnetic force and noise of claw pole alternators with different pole and slot combinations and phase number

Abstract

This study analysed the characteristics of electromagnetic force and noise of claw pole alternators with different pole and slot combinations and different phase number. The magnetic flux density in the airgap was first derived based on the magnetomotive force and permeance. Then the electromagnetic force was obtained using Maxwell stress tensor method. According to the analytical model, the spatial order and frequency of electromagnetic force can be expressed as the function of pole-pairs number p , slot number s and phase number m . Afterwards, the electromagnetic noise of three different alternators was tested in a semi-anechoic chamber. Combined with the 2D fast Fourier transform of electromagnetic force, the main force harmonics that caused the electromagnetic noise were distinguished. Finally, the relationship between the frequencies of electromagnetic force and noise and the number of pole-pairs and phase were established. Analysis result shows that for m -phase 2 p -pole/ s -slot integer slot claw pole alternators, the spatial order of electromagnetic force is kp ( k = 0, 1, 2, 3,...) and the corresponding frequency of these force harmonic is [±2 mpk ' + (± kp )] f r ( k ' = 0, 1, 2, 3 ...). The main order (frequency domain) of electromagnetic noise is 2 mp which is independent of the slot number.