Adaptive control for time-delay systems adopting Smith predictor models

Time delay phenomena generally exist in actual industry control systems, but it is difficult to achieve a satisfactory control effect by using of the traditional PID control method which also easily causes the instability of the system. The Smith predictor is an effective method widely applied in closed-loop controls for the time-delay systems, however, there are serious problems that the mismatching of the parameters between the Smith predictor model and the plant will give rise to bad control characteristics or even the system oscillation and divergency. In this paper, we propose a Lyapunov-stability-theory-based model reference adaptive control scheme for improvement of the control characteristics for the Smith predictor methods when the parameter mismatch occurs. We describe the basic principle and derive the adaptive control laws for first order plant models. Then the numerical simulations are carried out to verify this proposal. The theoretical analysis and simulation results indicate that the combination of Smith predictor methods and adaptive control evidently improves the control performance of time-delay systems and prevents the system instability, therefore partly solves the above problems of the Smith predictor and acquires rather good effect. We expect it has a wide range of applications to actual process controls for time-delay systems and equipment. © 2021, Editorial Department of Control Theory & Applications South China University of Technology. All right reserved.