ROBUST DIGITAL-CONTROL OF SYSTEMS WITH TIME-DELAY (THE SMITH PREDICTOR REVISITED)

The design of robust digital controllers for systems with time delay is investigated. A particular class of digital controller is considered, namely those for which the closed-loop poles include the poles of the system to be controlled. Robust design with respect to time delay variations requires the introduction of additional closed-loop poles and/or reduction of the gain of the feedback path at high frequencies (near 0.5 f(s), where f(s) is sampling frequency). Relationships with other robustification procedures are examined.