Automatic Tuning of PID Controllers

Abstract

Proportional Integral and Derivative (PID) controllers are the most frequently used controllers in the process industry over the years. The performance is a factor of adequate tuning. The knowledge of the process is critical to the tuning process as well selecting the right PID form and the tuning algorithm. Since there can be as many as possible PID loop in an industry, manually performing this task will take a lot of time and cause down time that can results to poor product quality as well as loss of income. Thus, there is a need for tuning to be done automatically, and this form the basis of this thesis, automatic tuning of PID controller. It’s therefore pertinent to adjudge the right tuning rule as well as selecting the right model for the process and thereafter if there are any changes in this model, to readjust the parameters used for the PID algorithms to get the right PID tuning parameter on real time basis. The standard form of the PID is used in the simulation and the relay feedback experiment by Åstrom is considered for the parameters adjustment, and the variant of this method developed by Schei is also investigated and the two methods compared. Implementation and evaluation of these methods were done with the quadruple tank and air heater processes. The relay experimentation is an easy process that ensured recursive parameter calculation based on identified point on the Nyquist plot and this method can be seamless automated with just a push point from the Operator.