| Control engineers rely on many tools, and although some people may think that in the future there will be one general universal tool that solves all problems, like model predictive control, this is not likely to happen. The main reason is that the possible benefits of using more general tools may not be worth the increased implementation costs (including modelling efforts) compared to using simpler "conventional" advanced process control (APC) solutions. In particular, this applies to process control, where each process is often unique. In addition, for a new process, a model is usually not available, so at least for the initial period of operation a conventional scheme must be implemented.
Conventional APC includes the “advanced” standard control elements that typically are provided at the DCS (distributed control system) level and which industry commonly uses to enhance control when simple single-loop PID controllers do not give acceptable control performance. Examples of such control elements are cascade control, selectors (override), split range control, input or valve position control (VPC), multiple controllers (and MVs) for the same CV, and nonlinear calculation blocks (including nonlinear feedforward and decoupling and linearizing adaptive gain elements).
Since its introduction in the 1940’s, about 80 years ago, conventional APC has largely been overlooked by the academic community, yet it is still thriving in industrial practice, even after 40 years with MPC. So, it seems safe to predict that conventional APC (including PID control) will not be replaced by MPC, but will remain in the toolbox along with MPC. The goal of this talk is to take a systematic view on how to design a conventional APC system. The starting point is the plantwide optimal steady-state economic operation, with focus on constraints.
| Sigurd Skogestad received his Ph.D. degree from the California Institute of Technology, Pasadena, USA in 1987. He has been a full professor at Norwegian University of Science and Technology (NTNU), Trondheim, Norway since 1987. He is the principal author, together with Prof. Ian Postlethwaite, of the book "Multivariable feedback control" published by Wiley in 1996 (first edition) and 2005 (second edition). His research interests include the use of feedback as a tool to make the system well-behaved (including self-optimizing control), limitations on performance in linear systems, control structure design and plantwide control, interactions between process design and control, and distillation column design, control and dynamics. His other main interests are mountain skiing (cross country), orienteering (running around with a map) and grouse hunting. He is a Fellow of the American Institute of Chemical Engineers (2012) and IFAC (2014).