Automatic tuning of PID controllers
The aim of the project is to develop second generation automatic tuning procedures for PID controllers. A prestudy was supported by PiiA-Vinnova, and industrial collaboration is made with Schneider Electric Buildings AB.
Methods for automatic tuning of PID controllers were developed in the early eighties, and implemented in industrial single-station controllers and DCS systems. A main reason was the technology shift from analog to computer-based controllers and systems at that time, which made implementation of such tuning functions possible. These methods were limited by the computer power and the knowledge about PID design that were available at that time. Since then, the computational power and the knowledge about PID design has increased, which provides the possibility to develop new tuning functions with better performance.
We aim at developing a methodology for automatic tuning of PID controllers, using nonlinear feedback for idenfication input generation and optimization based methods for both process parameter identification and controller synthesis.
The main components of the auto-tuning alogorithm are the following:
- Generate identification input with little or none a priori system information
- Transfer function parameter identification through optimization
- Model verification
- PID synthesis
- Performance evaluation
An approach for automatic tuning is to conduct a simple experiment, using an asymmetric relay function as feedback. From the experiment the static gain and the normalized time delay of the system can be estimated, and from this a FOTD model can be achieved from analytical formulas. The experiment data can also be used to find a higher order model using numerical parameter estimation methods. From the achieved model the parameters of a PI or PID controller can be tuned either by existing tuning rules or by optimization methods.