Object-oriented modelling of industrial PID controllers

This paper presents a library of (PID) controller models adopting the object-oriented approach, and written in Modelica. Peculiar to this work is that controllers are represented both as dynamic continuous-time and digital models, achieving consistence between the two and accounting for the functionalities of typical industrial implementations. This allows the designer to use realistic controllers, maintaining the possibility of choosing the continuous-time or digital (event based) representation. The former allows for example for variable-step simulation, to the advantage of efficiency, while the latter represents very realistically the actual control system's operation, clearly at the cost of more simulation time. Beside standard PI and PID controls, in this work also autotuning is (initially) considered, and some application examples are reported to show how the presented library can ease system studies involving (PID) controls.