Optimal closed-loop PID tuning in the process industry with the "iterative feedback tuning" scheme

In 1994, H. Hjalmarsson, S. Gunnarsson and M. Gevers developed an optimal iterative controller tuning method (IFT) whose major innovation was the absence of any explicit modeling stage. Data collected during a sequence of closed loop experiments drive the parameters updates in order to iteratively minimize a control performance criterion. The idea of improving the performance of a given controller without ever opening the loop has always been appealing for process control engineers and made it a good candidate for experimentation. After a brief presentation of the method, we propose extensions to solve some engineering problems and report some results gained on PID tuning in the chemical process industry.