Sliding Mode Control For Linear Uncertain Time-Delay Systems

Time delays and uncertainties are very common in various engineering systems,and both can cause instability and poor performance. Therefore the investigation ofrobust controllers for uncertain time-delay systems is very important both in theoryand in practice.One of the most distinguished features of the sliding mode control (SMC) is thatafter reaching the sliding mode, the system has robustness to matched parameteruncertainties and extemal disturbances. The system dynamics performance on slidingmode can be pre-designed, and the control algorithm is simple and easy to be realized.SMC is an effective robust control approach for uncertain systems, nonlinear systems,time-delay systems, time-varying systems and perturbed systems.In this thesis, the problem of designing sliding mode controllers for differentuncertain time-delay systems is studied. The main works are summarized as follows:1. The problem of designing optimal sliding mode controllers for a class ofuncertain linear systems with input time-delay is considered. A linear transformation isdefined to transform the original system into a delay-free form. Then based on thetransformed system, the design method of optimal sliding mode with a quadraticperformance index minimized is presented. The designed control law ensures theexistence of the sliding mode and has low chattering in the sliding motion. Thenumerical simulation study and the application in chemical process controldemonstrate the efficiency of the proposed method.2. For a class of uncertain systems with state time-delay, a design method of aglobal sliding mode controller (GSMC) is presented. A new type of integral slidingmode (ISM) is proposed which can ensure the global sliding mode during the entireresponse of the system. The sliding mode controller design process is presentedsystematically. The effectiveness of the proposed method is demonstrated by simulation study.3. For a class of uncertain linear systems with input and state delays, the problemof designing GSMC based on linear transformation is discussed. A lineartransformation is defined to transform the original system into a state-delay form. Thenbased on the transformed system, the design method of GSMC is presented. A newtype of ISM is proposed, which can ensure the global sliding mode during the entireresponse of the system. A robust control law is designed to ensure the existence of asliding mode and to overcome the effects of the uncertainties. Furthermore, theproposed method is used to control the networked control systems (NCS) withnetwork-induced time delays. Simulation results verify that the proposed method canguarantee the NCS's stability and also have good robustness.4. The conclusions are given finally. And the directions for the future researchwork are indicated.