A frequeno' domain methodology Jor the design of practical, low order controllers Jor processes involving relatively large dead time is' presented. The methodology consists of determining the optimum structure and parameters of the controller so that the closed loop disturbance response matches the response of a pre-specified reference model. This approach allows the designer to directly incorporate acceptable disturbance rejection characteristics for the closed loop system in the early stages of design.
The most important task in the methodology is" the selection of an appropriate refi~rence model.
It is" shown that the reference model must meet certain mathematical conditions to guarantee physical realizability of the controller and the internal stability of the system.
A reference specification procedure is developed to provide a large margin of robustness for the design while assuring a .fast decay of the disturbance response. The power (~[ the methodology is demonstrated by several non-trivial design examples pertaining to stable, unstable and non-minimum-phase process models with significant dead time. The tradeoff between robustness and response speed is discussed and illustrated.