Abstract − This paper presents an autotuning process controller aimed at providing efficient rejection of load disturbances, in a class of situations that are typical in process cotnrol, and not easy to treat with most standard autotuning controllers. The regulator structure is not completely fixed a priori, though it can be reduced to a PID in simple cases. This is a significant peculiarity with respect to the main research stream on autotuning regulators, that refers essentially to fixed-structure (PID) regulators. Both a simulation and a laboratory example are reported.
I. INTRODUCTION
In the industry, the term ‘process controller’ refers typically to a simple device, handling one or a few loops. Such devices are the most widely used in process applications (64% of the overall marketplace according to [5]), as they “provide a more manageable process in case of failure” (ibidem). In the selection of a process controller, autotuning is nowadays among the most desired features [6], as the users are becoming more and more confident in that technology [3, 2, 13]. Most process controllers are based on the PID regulator structure, and the diffusion of those controllers is surely among the reasons of the great research effort that in the last decades has been spent on the PID (auto)tuning [2, 13]. Methods were conceived to synthesize a PID for almost any control problem, or class of control problems, that a process controller may come across. This work addresses a control problem that is quite particular, but of significant interest in process applications, and for which it is difficult, and potentially very critical, to devise a tuning method for the PID. For this control problem, an alternative regulator structure is proposed, and a tuning procedure for that structure is devised, focusing attention on implementation-related issues. A simulation test and an experimental laboratory example are reported to illustrate the effectiveness of the proposed autotuning regulator, also by comparing it to a PID tuned with a method conceived for load disturbance rejection.
