Back- emf infleunce in BDCM design for commutation torque riple reduction

In this paper, we study the effect of the back-emf waveform on the commutation torque ripple of a BDCM supplied with 120° mode controller. Various forms of back-emf are obtained through segmentation of the magnet into two pieces that have either V or U shape. The Torque and the torque ripple are determined from Indirect Circuit coupling approach, in Matlab-Simulink environment. Initially, the back-emf is determined by finite element method in 2D then is integrated into a model that accounts for the motor and its converter. After validation the model of study using an experimental kit based on an industrial motor with a magnet in one segment per pole, we have carried out the segmentation of the magnets while varying the angle of inter segment considering the magnet edges in U and V shape. Based on same approach, we determine the torque and its ripple for each new structure. An optimum design was found for the two shapes of segmentation. For the segmentation in the V shape, the minimum of torque ripple was found less than 6%, whereas in the U shape, the minimum was approximately less than 9%, in comparison to the 40% resulting from the original motor without magnet segmentation.