Numerical computation and implementation of H-infinity controllers for retarded and neutral time delay systems

Abstract

Being the most commonly encountered systems in engineering applications, design of robustly stabilizing H∞ controller with maximum performance for timedelay linear time-invariant systems has been an attractive topic in control theory for many decades. A Matlab package called HINFCON is published in 1996. It applies an early solution to the problem, the so-called Toker-Özbay formula. It assumes that the coprime factorization is given, and computes the optimal performance level and the corresponding optimal controller through a manual iteration. The software introduced in this thesis, combines HINFCON with another Matlab package, YALTA, that is being used to do stability analysis for neutral/retarded systems, to perform coprime and inner-outer factorizations of the given infinite dimensional system. Additionally, an iterative algorithm for computation of optimal performance level automatically is implemented to prevent any manual computation. Finally, the Matlab command fitfrd is incorporated into the software that is used for approximation of the optimal controller to obtain a robustly stabilizing suboptimal finite dimensional controller. This thesis also introduces a new structure of the optimal controller which is more reliable and implementable on practical systems. Various examples are solved to compare the suboptimal controllers obtained by using the new structure with direct approximation of plant and optimal controller.