Design for Feedback Systems With Plant Input Amplitude and Rate Saturation

Abstract

In this paper, a method of compensation for feedback systems subject to simultaneous plant input amplitude and rate saturation is presented. It applies to uncertain, stable plants of a type greater than or equal to 1. Founded on Horowitz’s original idea for amplitude saturation compensation (, 1983, Int. J. Control, 38(1), pp. 169–197) and extensions developed in (, and , 1999, Proceedings of American Control Conference, San Diego, CA, pp. 3046–3050; , and , 2001, ASME J. Dyn. Syst., Meas., Control, 123(2), pp. 225–232; , 2000, Ph.D. dissertation, Texas A&M University), a synthesis method that explicitly takes into account input amplitude and rate saturation is further developed. In the case of simultaneous amplitude and rate saturation, approaches developed separately for amplitude alone, and rate alone saturation (, 2000, Ph.D. dissertation, Texas A&M University), respectively, are integrated into one method, and results in a 4DOF(degrees of freedom) feedback system with two extra compensators to deal with two saturation nonlinearities. Design constraints for saturation compensation are developed and expressed as frequency domain bounds. Synthesis of the two additional compensators follows from loop shaping methods, such as QFT. This approach guarantees input/output stability for the class of plants considered. Examples are given to illustrate the application of this approach.