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 fs , where fs is sampling frequency). Relationships with other robustification procedures are examined.