Commutation torque ripple of four-switch, brushless dc motor drives, part II: controllability and minimization

In part I of this paper, commutation torque ripple of a four-switch, three-phase inverter (FSTPI) brushless dc motor drive (BLDC) was analyzed in details. This paper presents a comprehensive study on the controllability and reduction of the generated commutation torque ripples. It's shown that the conventional techniques for controlling of the phase current in a FSTPI brushless dc motor drive are practically effective in low speed and can not reduce the commutation torque ripple in high speed range. Therefore a novel current control technique is developed to minimize the commutation torque ripple for entire of speed range. The technique proposed here is based on a strategy that the current slopes of the rising and the decaying phases during the commutation interval can be equalized by proper duty-ratios in the six operation modes