GAIN MARGIN IMPROVEMENT USING GENERALIZED SAMPLED-DATA HOLD FUNCTION-BASED MULTIRATE OUTPUT COMPENSATOR

For a SISO, strictly proper, nonminimum-phase, continuous-time, linear time-invariant (LTI) plant, it was shown in Yan, W., B. D. O. Anderso n and R. R. Bitmead (1993). IEEE Trans. Automat. Contr., that the clos ed-loop gain margin obtained via a generalized sampled-data hold funct ion (GSHF) based dynamic compensator is significantly improved over th at achieved via a conventional periodic controller used in Francis, B. A. and T. T. Georgiou (1988). IEEE Trans. Automat. Contr., AC-33, 820 -832. Nevertheless, the compensator so designed is not necessarily str ictly proper. It is well-known that it is practically difficult and so metimes impossible to implement a nonstrictly proper compensator due t o the requirement of zero computation time. Further, as has been shown in Vidyasagar, M. (1985). Systems and Control Letters, 5, 413-418, st abilization by a nonstrictly proper controller is never robust against singular perturbations. In this paper, we propose a new type of GSHF based compensator which employs multirate sampling of the plant output . Using the proposed compensator, not only the same level of gain marg in as in Yan, W., B. D. O. Anderson and R. R. Bitmead (1993). IEEE Tra ns. Automat. Contr., can be achieved, but also, more importantly, the compensator is strictly proper.