Commutation Torque Ripple Minimization in Direct Torque Controlled PM Brushless DC Drives

This paper describes an improved implementation of direct torque control (DTC) to a permanent magnet brushless DC drive (BLDC). The commutation torque ripple, which occurs every 60deg elec. in a conventional 3-phase BLDC machine, with 120deg elec. 2-phase conduction, is reduced by employing a hybrid 2-phase and 3-phase switching mode during the commutation periods. It is based on the criterion of minimizing the torque error between the commanded torque and the estimated torque, and does not require knowledge of the conduction duration of the 3-phase switching mode. It adaptively adjusts the phase current waveform to maintain constant electromagnetic torque, so that commutation torque ripple, which would have resulted with existing DTC at high speeds, is effectively eliminated, as confirmed by both simulations and measurements