Copyright (i) IFAC Digital Control: Past, Present and Future of PlO Control, Terrassa, Spain, 2000 CONTROL DESIGN FOR PID CONTROLLERS AUTO-TUNING BASED ON IMPROVED IDENTIFICATION R. R. Pecharroman and F. L. Pagola Department oj Electronics and Automatic Control, E. T.S. de fngenieria (lCAf). Universidad Pontificia Comillas de Madrid, Alberto Aguilera 23, 28015 Madrid, Spain. Phone 34915422800, ramon@dea.icai.upco.es,pagola@dea.icai.upco.es Abstract: Every auto-tuning method for PID controllers has two steps: identification of the process and design of the controller. An identification procedure to obtain two points of the frequency response of the system was presented in (PecharrOlmm and Pagola, 1999). This paper develops a design method based on the ITAE index. This design procedure is then related to the results of the process identification, yielding a complete auto-tuning method that gives very good results in theory and in practice. A complete test batch is used. The main contribution is that the method is valid for integrating as well as non-integrating processes. Copyright © 2000 fFAC Keywords: Autotuners, PID Control, Integral performance indices, Least-squares approximation, Process models. I. INTRODUCTION Most controllers used in industry are of PID type. Very often, their performance is poor due to, among other factors, inadequate tuning of the controller parameters (Astrom and Hiigglund, 1995). Hence, auto-tuning is a very desirable feature and almost every industrial PlO controller provides it nowadays. There are many different auto-tuning methods, several of them compared in (Hang and Sin, 1991). An auto-tuning method consists of a process identification procedure plus a controller design procedure. Very often, these two aspects are not clearly differenciated. Most auto-tuning methods fail in certain cases, but it is not clearly analysed wether the problem is due to the identification or to the controller design step. It might be possible to build an auto-tuning method using the identification procedure proposed by one author and the controller design procedure proposed by another one. This paper 85 focuses on the controller design step and on the integration of both to give a complete auto-tuning method. The identification step was presented in (Pecharroman and Pagola, 1999). A modified PlO algorithm is used, incorporating valuable advances presented in the literature: two- degree-of-freedom structure, setpoint weighting, etc. The controller-parameter tuning is based on the ITAE performance index, subject to a damping measure, the maximun sensitivity junction. The optimization is performed in two steps, allowing simultaneous quasi- optimization of responses to both setpoint and load disturbance changes. This method is applied to all the plants included in the test batch shown in the Appendix, that intends to represent the industrial practice. The results are very good. The next goal is to relate this controller design method to the results of the identification step: two points of the frequency response of the process (the