Simple Analytical Design of Modified Smith Predictor with Improved Performance for Unstable First-Order Plus Time Delay (FOPTD) Processes

Abstract

A simple method of designing the controllers for the modified Smith predictor scheme with improved closed-loop performances is proposed for open-loop unstable first-order plus time delay (FOPTD) processes. The proposed method consists of two controllers that are meant for different objectives, namely, the set-point tracking and simultaneous stabilization of the unstable process with time delay and the load disturbance rejection. The design steps of these two controllers are independent. The direct synthesis method is used to design the set-point tracking controller, and simple analytical tuning rules are provided for the load disturbance controller. Robustness studies on the stability and performance are provided, with respect to the uncertainties in the unstable process model parameters. The proposed scheme consists of only one tuning parameter. Good nominal and robust control performances are achieved with the proposed method. Significant improvement in the closed-loop performances are obtained, when co...