Feedback–Feedforward Compensation of a DC Motor

The separately-excited DC motor is a high-performance variable speed drive vital for industrial applications such as robotics, actuation, control and guided manipulation because of its precision, simplicity, continuous control feature and wide speed range. Hence there is need to regulate and drive the motor at desired speed in the presence of parameter variations, model uncertainties and external disturbances. The ubiquitous Proportional-Integral-Derivative controller is not the optimal control strategy to achieve this objective because of its oscillatory response, and sensitivity to load disturbances and motor parameter variations. Hence this paper proposes a Feedforward - Feedback control scheme, for armature voltage speed control, that will permit the design of two distinct control objectives; that is setpoint tracking with acceptable robustness and disturbance rejection. This combined scheme ensures high performance for the DC motor speed where the model-based tuned feedback action is used to guarantee reference speed tracking and to compensate for conceivable model inaccuracies while feedforward compensation maintains the output speed at the setpoint in spite of arbitrary changes in the disturbance variable. Computer simulations are then presented to show the effectiveness of the proposed scheme.