ROBUST PARAMETRIC CLASSICAL CONTROL DESIGN

This paper extends well-known graphical design tools such as the Nyqui st plot, Bode plot, and Nichols charts to the domain of control system s containing parameter uncertainty. We have specifically considered li near interval control systems, namely those where the uncertain parame ters appear linearly in the characteristic polynomial and vary in inte rvals, because in these cases exact construction of frequency envelope s is possible. Using these developments, we calculate various extremal stability margins for such systems, and these are used with standard classical control design techniques to deal with robustness with respe ct to parametric uncertainty. In addition, we give an effective techni que to iteratively select values of the design parameters within given ranges so that the closed loop system produces improved gain or phase margin.