Analysis of torque ripple in electronically commutated permanent magnet machines and minimization methods

The authors deal with permanent magnet machines with rectangular induction and current waveforms. In order to minimize the machine torque ripple, the evolution of the torque curves of the different windings supplied with constant current in function of the position of the rotor, must have a trapezoidal shape comprising a plateau with the correct width. They must be correctly juxtaposed by an adequate choice of the supply sequences. Moreover, in order to get the most out of the torque, an optimal use of the air-gap must be made by making the largest number of conductors work simultaneously. The influence of different parameters on the constant current torque curve shape are examined. The different ways of combining these torque curves are analysed so as to come to the best use of the air-gap and minimize the resulting torque ripple at the same time