Control of input/output delayed and disturbed unstable plants

In this survey paper, different approaches to deal with input/output time delayed disturbed plants are considered. First, the classical Smith predictor and some of its modifications to deal with unstable and non-minimum phase plants are reviewed, being applied to single-input-single-output (SISO) plants. Then, combining the internal and external representation, a generalized dead-time compensator (DTC) is introduced. This new predictor provides a general solution for SISO plants, but fails when considering multi-input-multi-output (MIMO) plants, with different delays in each input/output channel. A detailed control design procedure is reviewed for these complex plants and some examples illustrate the controller design. Some suggestions for further improvements are also outlined.