Comparison of Linear Controllers for Nonlinear, Open-loop Unstable Reactor

Mohammad Khalili
University of South-Eastern Norway, Norway

Bernt Lie
University of South-Eastern Norway, Norway

Ladda ner artikelhttp://dx.doi.org/10.3384/ecp18153185

Ingår i: Proceedings of The 59th Conference on Simulation and Modelling (SIMS 59), 26-28 September 2018, Oslo Metropolitan University, Norway

Linköping Electronic Conference Proceedings 153:26, s. 185-192

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Publicerad: 2018-11-19

ISBN: 978-91-7685-494-5

ISSN: 1650-3686 (tryckt), 1650-3740 (online)


Many industrially important reactors are operated over a regime where they exhibit nonlinear behavior. Exothermal reactors are often open-loop unstable. For such reactors, safe operation with good performance requires good control. We have considered linear controllers and tested these on a simple chemical engineering non-linear, open loop unstable model and an extension of the model in order to do a basic test of model uncertainty. Specifically, a PI controller has been tuned and tested, the operation of an Extended Kalman Filter (EKF, KF) has been tuned and tested. Based on feedback from estimated states in the EKF, a linear quadratic controller with integral action (LQG+I) has been tuned and tested; the study has been carried out using MATLAB for KF and LQG+I tuning; the remaining study has been carried out in a Jupyter Notebook using Python in tandem with Modelica. The PI controller lead to negative cooling water temperature upon a step change in temperature reference. When constraining the input to liquid water with anti-windup, PI control gives considerable undesirable overshoot in the reactor temperature. The LQG+I controller performs much better wrt. temperature overshoot. Overall, the reported work has demonstrated how a modern simulation set-up (OpenModelica + Python) can be used for model based control analysis and design.


nonlinear reactor, model uncertainty, control design, PI control, LQG control


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