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Title Control of Urea Injection for an Automotive SCR Application
Author Thorsteinsson, Solveig
Supervisor Jørgensen, John Bagterp (Scientific Computing, Department of Informatics and Mathematical Modeling, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Huusom, Jakob Kjøbsted (Computer Aided Process Engineering Center, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2011
Abstract In this project, a soft model predictive controller (MPC) used to control the injection of urea in the urea-SCR system, has been investigated. The control objectives have been specified in accordance with the emission limits of the Euro VI emission standard. Furthermore, an optimization problem reflecting the control requirements has been formulated. An offset-free model predictive controller based on ARX models has been implemented, and the implementation has been successfully validated. The corrective actions qualitatively have been shown to be appropriate, thus indicating that the control methodology is applicable for controlling the urea- SCR system. Tuning of the closed loop system has been carried out in simulations using a dynamic model developed at Haldor Topsøe A/S to approximate the actual physical system. The tuning has been complicated due to difficulties in reaching steady state conditions, and besides, long computation times have been limiting factor for the number of simulations conducted. Consequently, an optimal tuning has not been achieved for the offset-free soft MPC. This has been reflected in simulations of transient cycles, where a maximum NOx conversion of 75.4% has been achieved which is dissatisfactory. With the purpose of narrowing the problem, the optimization problem has been reduced to nominal MPC, and the behavior of the closed loop system has been investigated. This has revealed that the description of the dynamics by the estimated offset-free ARX is deficient. Despite the difficulties in meeting the control objectives, the qualitative results from the presented design activities can be used as a basis of further improvements and a number of possible future improvements is suggested.
Imprint Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Series IMM-M.Sc.-2011-22
Fulltext
Original PDF ep11_22.pdf (2.47 MB)
Admin Creation date: 2011-04-27    Update date: 2011-04-27    Source: dtu    ID: 276344    Original MXD