PID Controller With an Autotuning Function

Abstract

The optimal setting of parameters of PID controllers is a significant requirement of industrial practice. It seems intuitive, but it can be complicated, especially when there are many (often conflicting) requirements for the control process. Many regulators are then set incorrectly or inappropriately. The search for a method of identifying the parameters of the controlled system with the subsequent setting of the parameters of the PID controllers takes place from the moment it is found. Nevertheless, we decided to develop a physical controller that would be easy to use in industrial practice. The demand is that the operator set as few parameters as possible, and most of the settings should be automatic. We based the identification on the relay method, more precisely, on its modification known as the relay-shifting method. During identification, an asymmetric relay is used. The parameters of a model of the system are then calculated from three points of the frequency characteristic. This method is not as commonly utilized in current commercial controllers. The general advantages of the relay method include identifying the system in a closed control loop and performing time-saving calculations. This makes it suitable for practical use in industry. The parameters of the PID controller are calculated using either the Marchetti-Scali method or the Ackermann method from the model whose parameters were obtained by relay identification. We built the controller on a development microcontroller board, which we supplemented with the necessary peripherals. The result is a prototype of a physical PID controller with autotuning. In the article, we present not only the implemented equations but also the test results of our PID controller on one of the real devices on which its functionality was verified.

Keywords

• Autotuning
• identification
• PID control
• practical realization
• relay-shifting method