Precise accelerated torque control for small inductance brushless DC motor

In this paper, precise accelerated torque control for a small inductance brushless dc motor (BLDCM) is achieved by electromagnetic torque control and disturbance torque suppression. First, the electromagnetic torque ripple is reduced in commutation and conduction regions. In the former region, the ripple is suppressed by overlapping commutation control and optimizing the duty ratio of the active controller. In the latter region, the unbalance ripple caused by the unbalanced three phase windings is reduced by the proposed asymmetry compensation function, and the disturbance ripple created by the back electromotive force (EMF) is compensated by feedforward control. Second, the disturbance torque has been observed and compensated through the improved disturbance torque controller whose compensation coefficient is obtained by line-to-line back EMF coefficient estimation. And, both the disturbance observation and speed measurement are all synchronized with the encoder pulse alteration. Experimental results are presented to demonstrate the validity and effectiveness of the proposed accelerated torque control scheme.