Iterative Learning Approach Toward Closed-Loop Automatic Tuning of PID Controllers

This paper proposes a new method for closed-loop automatic tuning of a proportional-integral-derivative (PID) controller based on a new iterative learning control (ILC) approach. The proposed approach is applicable to process control applications where there is usually a time-delay/lag phenomenon and where nonrepetitive step changes in the reference signal are far more common than repetitive ones assumed in most literature on ILC. The method does not require the control loop to be detached for tuning, but it requires the input of a periodic reference signal which can be specified by the user or derived from a relay feedback experiment. A modified ILC scheme iteratively changes the control signal by adjusting the reference signal only. The learning gain can be selected to satisfy a necessary and sufficient condition derived in the paper, based on the information available from the oscillations induced. Once a satisfactory performance is achieved, the PID controller is then tuned by fitting the controller to yield a fitting input and output characteristic of the ILC component. Simulation and experimental results are furnished to illustrate the effectiveness of the proposed tuning method.