Robust linear controllers for unstable systems with time delay

The paper is concerned with the robust control design for linear uncertain systems having time delays. The proposed control synthesis is based on general solutions of Diophantine equations in the ring of Hurwitz stable and proper rational functions R-PS and the Youla-Kucera parametrization of controllers is utilized. The methodology covers both stable and unstable transfer functions. Several approximations of the time delay term is investigated and compared for unstable and integrating processes. The robustness is studied through the infinity (H,,,,) norm and the sensitivity function. Resulting control laws are of a general PID type and a scalar tuning parameter influencing robustness and properties of the closed loop system was introduced. Copyright (C) 2000 IFAC.