Uniting two local output controllers for linear system subject to input saturation: LMI approach

In this paper, we solve the problem of hybrid output unification of two local output feedback controller U-0 and U-1 for linear systems subject to input saturation. The closed-loop system with the controller U-0 has a smaller region of attraction R-0 and higher decay rate sigma(0), while the closed-loop system with U-1 has a larger region of attraction R-1 and a slower decay rate sigma(1), R-0 subset of R-1 and sigma(0) > sigma(1). To the best of our knowledge, the problem of unification of two local output feedback controller, has been solved only in the recent papers [17] and [2]. In [17], the problem of unification of two output controller is solved by using two norm estimators and a trigger time tau* to switch from the "global" controller to the "local" one, where it is defined in [17] and chosen sufficiently large. The work [2] proves that it can be selected arbitrarily small. Such choice of tau* minimizes the use of the slow controller U-1 and, thus, ameliorates the performance significantly. In this paper, the solution of the unification problem is formulated by means of linear matrix inequalities (LMIs), which can be easily verified numerically. The numerical example given in this paper compares the performance of the proposed hybrid controller with hybrid controllers in [17] and [2]. (C) 2018 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.