Robust Tuning and Performance Analysis of 2DoF PI Controllers for Integrating Controlled Processes

The aim of this paper is to present a robust tuning method and a closed-loop performance analysis of two-degree-of-freedom proportional integral controllers for integrating controlled processes. A closed-loop model reference optimization method has been followed with nonoscillatory and under damped response targets. It has been found that nonoscillatory response targets produce smoother controller outputs and that the regulatory and servo-control performance (integrated absolute error and setting time) may be improved if lightly-under-damped responses are allowed. The proposed tuning method allows the designer to deal with the performance/robustness trade-off of the resulting closed-loop control system by specifying the desired robustness level through selecting a maximum sensitivity in the range from 1.4 to 2.0. Controller tuning equations that guarantee the design robustness level are provided for integrating second-order plus dead-time models with normalized dead-times in the range from 0.1 to 2.0, and integrating plus dead-time models. The robustness of the control system is analyzed. Comparative examples show the effectiveness of the proposed tuning method. The exact achievement of the control system robustness target for all the integrated controlled processes models considered is the distinctive characteristic of the proposed model reference robust tuning method.