Stability Analysis of Networked Control Systems with Time Delay

Abstract

Networked control systems (NCSs) involves the transmission of measured data from plant site to the control centre and control information from the control centre to the plant site. Time-delay is a predominant issue that may cause stability issues in NCS. Although time-invariant delay occurs in a dedicated communication channel, future implementation of open communication channels in NCS gives rise to different characteristics of time-delays. The stability analysis of electrical systems with different delay characteristics such as time-invariant delay, time-varying delay (TVD), interval TVD and additive TVDs are carried out using Lyapunov-Krasovskii (LK) functional and linear matrix inequality (LMI) techniques. Delay-dependent stability (DDS) criteria are presented for these delay characteristics using the time-domain methods. The maximum proper estimation of delay bound for the system with various time-delay effects decides the conservativeness of the proposed DDS criterion. These delay bounds are determined for various NCSs in this thesis. newlineThe thesis work is mainly divided into two parts. DDS criteria are presented for the system with time-invariant delays by selecting an LK functional and imposing an effective bounding techniques. The employment of Wirtinger inequality as a bounding techniques and discrete delay-decomposition approach over the formulation of stability condition. In the sequel, DDS criteria are presented for TVDs formulated using free-weighting matrices, reciprocal convex lemma and extended reciprocal convex combination lemma as a bounding technique for time-derivative of the LK functional. All the results reported in this thesis are presented in the LMI framework and effectiveness of corresponding results are highlighted with the help of time-delayed electrical systems.