Robust design of discrete-time two-degree-of-freedom matched servo systems

A robust design methodology for discrete-time two-degree-of-freedom control systems is presented on the basis of Zakian's principle of matching, with an emphasis on time-domain performance. The feedforward and feedback controllers are designed in such a way that, in spite of plant uncertainty, the tracking error and the control input are kept within prescribed bounds on the assumption that the reference input is bounded in magnitude and rate of change, and the disturbance is bounded in magnitude. A practical design criterion that ensures robust stability and robust performance in time-domain is given. The presented methodology is tested and its effectiveness is verified on a speed control system of a DC servomotor.