Industrial test setup for autotuning of PID controllers in large-scale processes: Applied to Tennessee Eastman process

Abstract

Although many PID tuning approaches are available, it is not easy to find a method that does not require any engineer/operator interference. In this work, we present a fully automated approach for PID tuning based on relay feedback. This method involves sending the relay feedback test data from PLCs (Programmable Logic Controller) into a historian, analyzing the test data using a tuning application to generate a tuning report that contains PID parameters and sending the report back to the operator station to retune the controllers in PLCs.This paper is focused on the following three keys steps: 1) A method to identify persistent steady-state conditions in a control loop using routine operating data because any tuning test is performed when the process is operating at steady state, 2) A novel procedure to implement relay based tuning test, 3) A new model identification method which is a combination of frequency-domain and time-domain analysis. Subsequently, the identified plant model is used to obtain PID tuning parameters based on IMC design.The approach has been tested on an industrial test setup in which all the control loops of the Tennessee Eastman process are controlled by a Siemens PLC. The necessary relay parameters, the hysteresis and relay amplitude, for the test are estimated automatically where interference by an engineer or an operator is not required. The new method for model identification is robust against measurement noises. The proposed method is able to tune the important control loops in the Tennessee Eastman process successfully.