Zero-ripple torque control in BLDC motors : a straightforward approach

Abstract

The subject of zero-ripple torque control in Brushless DC Motors (BLDCM’s) has gained importance due to the growing popularity of small electric motors in consumer electronic applications. A low number of phases and the occurrence of production tol erances give rise to low-frequency torque errors, which manifest themselves as relatively large position errors due to the low inertia of these small drives. With regard to the tight specifications of the controlled performance, reduction of these low frequent torque errors is desirable. In literature, two main approaches have been demonstrated for the analysis and mini mization of torque ripple. One approach is based on Fourier analysis, while the other uses variation calculus to find optimal current waveforms. In this paper, a new approach for the determination of optimal current waveforms is presented. The approach is based on elementary differential calculus, and can be used even in the case when both the back-emf’s and the stator resistances show asymmetry. The new approach is compared to the Fourier method in a test case, and shows significant reduction in RMS and average values of the stator currents needed to generate a desired torque