A unified step response procedure for autotuning of PI controller and Smith predictor for stable processes

The step response autotuning of PI controller and Smith dead-time compensator (DTC), for stable processes, is studied in detail. A simple and effective procedure proposed is based on the first-order plus dead-time model, obtained from the step response by measuring the time to go to ten and sixty three percent of the steady-state value of the process output. The tuning formulae derived contain an adjustable parameter, with a clear meaning with respect to the performance/robustness, enabling the user to specify its value within a well defined range, in accordance with the expected range of process parameter variations and the controller used (PI or DTC). Comparison with recently proposed methods and experimental results presented confirm that high and consistent closedloop system performance/robustness are obtained for a wide range of dynamic characteristics common to industrial processes.