Minimizing the Influence of Cogging Torque on Vibration in PM Brushless Machines by Direct Torque Control

This paper applies direct torque control (DTC) to a permanent magnet (PM) brushless machine, which maybe either brushless AC or DC, highlights the difference in its implementation when cogging is considered, and compares the performance which is achieved both with and without a consideration of the cogging torque. It is shown that DTC can automatically compensate for the influence of cogging torque which may have any waveform if it is accounted for in the estimated torque equation, in a similar manner to considering an external load. The method results in a simple control algorithm and significantly reduced torque ripple. Its effectiveness is validated by vibration measurement on a 3-phase, 10-pole, 12-slot brushless DC motor.