Towards ?plug and control?: self-tuning temperature controller for PLC

Abstract

Software PID controllers have become a standard component of automation with PLCs (programmable logic controllers) and work together with classical sequential function charts in the same processing units. However, traditional methods for the computer-aided design of control systems often involve high mathematical effort and are usually implemented on additional PCs that are only connected for commissioning purposes. Therefore a new, very simple concept for self-tuning PID controllers will be presented, which is implemented together with the controller on the PLC and which enables automatic tuning without prior knowledge of the process. The concept is designed specifically for temperature control, but can also be used for other control loops in the process industry which show stable time-lag dynamics and allow sufficient setpoint steps. For users, the most important advantage is the drastic reduction of commissioning time and effort. If, for example, there are 10 temperature loops in one machine, the successive tuning of all 10 controllers used to require several days. With the new concept, there is no longer any need for dedicated tuning. The self-tuning of all control loops is performed automatically and simultaneously on machine startup. Control performance is better than it is with the traditionally designed PID controllers, particularly for slow temperature processes. The concept is based on a systematic startup sequence to explore process dynamics, a modified inflection point method for process identification and a separation of setpoint and disturbance control. Copyright © 2000 John Wiley & Sons, Ltd.