Tracking with an H/sup/spl infin// Criterion - Decision and Control, 1997., Proceedings of the 36th IEEE Conference on

In this paper we study the problem of tracking a reference signal from the H" point, of view. As opposed to general Woo problems, whcrc only suboptimal solutions are obtained, wc show that for both the full information arid measurement, feedback tracking problems the H""-optimal solutions can be explicitly found. The results also indicate an interesting dichotomy between minimum phase and non-minimum phase plants: for minimum phase plants the best causal tracker performs as well as the best noncausal tracker, whereas for nonminimum phase plants, causal trackers cannot reduce the H" norms from their a priori values. We also mention some remedies for the non-minimum phase case, such as adding more actuators (control inputs) or allowing for some finite delay. For causal tracking of nonminimum phase plants, we show that a delay equal to at, least the number of non-minimum phase zeros of the plant is required.