Abstract: The advantages and disadvantages of Smith predictors were discussed‚by means of which a modified Smith predictor was proposed．The closed-loop feedback control scheme was applied to the modified predictor‚thus making the predictor be of a simple structure and be capable of tracing the process disturbance．Processes with integral action were then simulated．The results indicate that the modified predictor is of the similar performance as conventional Smith pre-dictors when the models match well‚and is of a better stability than the conventional ones when the dismatching models were corrected．

Key words: Smith predictor, PI control, model matching, long time-delay