Robust digital control of systems with time delay (the Smith predictor revisited)

The paper investigates the design of robust digital controllers for systems with time delay. A particular class of digital controllers 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 will require introduction of additional closed loop poles and/or reduction of the gain of the feedback path in the high frequencies (near 0.5 f_S, where f_S=sampling frequency). Relationships with other robustification procedures are examined