Stability of saturated dead-time compensating pi controllers for uncertain dead-time systems

This paper analyzes the global stability of a dead-time compensator when considering a saturation in the control action and uncertainties in the estimation of the dead-time. The analysis is made using a first order plant with dead-time controlled by a Smith predictor plus a pi controller, that is, a scheme commonly used in the process industry. Using a frequency domain analysis the stability and the bifurcations of the system are analyzed when a saturation is included in the control system. The obtained results suggests the use of filters to avoid the undesirable effects produced by the error in the estimation of the dead-time and the saturation. The design of these filters is based on the stability analysis performed in this paper and gives less conservative results than the ones obtained using others approaches. In order to illustrate the results, some simulation examples are shown.