Model reference robust tuning of 2DoF PI controllers for integrating controlled processes

The aim of this paper is to present a robust tuning method of two-degree-of-freedom (2DoF) proportional integral (PI) controllers for integrating controlled processes. This is based on the use of a model reference optimization procedure with servo and regulatory closed-loop transfer functions targets. The designer is allowed to deal with the performance/robustness trade-off of the closed-loop control system by specifying the desired robustness level through selecting a maximum sensitivity in the range from 1.4 to 2.0. In addition, a smooth servo/regulatory performance combination is obtained by forcing both closed-loop transfer functions to perform as closely as possible to non-oscillatory dynamic targets. Controller tuning equations that guarantee the design robustness level are provided for integrating second-order plus dead-time (ISOPDT) models with normalized dead-times from 0.1 to 2.0, and integrating plus dead-time (IPDT) models. The robustness of the control system is analyzed. Comparative examples show the effectiveness of the proposed tuning method.