Local and global controllers for decentralized discrete-time variable structure control technique for large-scale systems

Abstract

This thesis presents a research on new discrete-time integral variable structure controllers for large-scale systems in the presence of matched and unmatched uncertainties. It is found in the literatures that limited works have been done on variable structure control for discrete-time large-scale system. Current computer technology allows direct implementation of discrete-time controller to control a system with greater simplicity and cost saving. The controllers developed in this research are able to achieve system stability in terms of both global and local controls. A global controller makes use of feedback from all subsystems to achieve the quasi-sliding surface and remains on it, with better performance than local controller. A local controller is able to perform the controlling task with feedback solely from the local subsystem itself, with simpler design but is compromised in performance. New theorems with mathematical proof for both local and global controllers are presented and simulations are carried out using Matlab for three different types of large-scale systems to test the proposed controllers. The simulation results also showed that the global controller has better performance than the local controller. Discrete-time integral variable structure control lets the implementation of the controller for large-scale systems a much more straight forward approach with computer. Furthermore, the characteristic of robustness in variable structure control ensures systems fast convergence to the desired value and rejects uncertainties and disturbances, which makes it very practical to be applied to many large-scale systems in real world applications. These newly developed controllers are able to provide cost effective implementations of discrete-time variable structure controllers using current digital hardware for various large-scale plants such as petrochemical, traffic control, telecommunication and robotic system.