Should we forget the Smith Predictor?

Abstract

The PI/PID controller is the most used controller in industry. However, for processes with large time delays, the common belief is that PI and PID controllers have sluggish performance, and that a Smith predictor or similar dead-time compensator can give much improved performance. We claim in this paper that this is a myth. For a given robustness level in terms of the peak sensitivity (Ms), we find that the performance improvement with the Smith predictor is small even for a pure time delay process. For other first-order processes a PID controller is generally better for a given robustness level. In addition, the Smith Predictor is much more sensitive to time delay errors than pi and pid controllers.

3rd IFAC Conference on Advances in Proportional-Integral-Derivative Control, Ghent, Belgium, May 9-11, 2018