Control of Selective Catalytic Reduction Systems Using Feedback Linearisation

This paper discusses the identification and control of a selective catalytic reduction SCR system. SCR after-treatment systems form an important technology for reducing the nitrogen oxides, NOx, produced by diesel engines. To be able to control the system, i.e. reducing the output NOx, good models of the after-treatment system are essential. In this paper a nonlinear black-box model is identified using a recursive prediction error method. The nonlinear model is applied for design of a controller using feedback linearization techniques including an adaptive strategy. A linear quadratic Gaussian controller is used for the control of the linearized system. A total of 17 parameters were estimated for the nonlinear model. The results indicate that output NOx control using feedback linearization based on a second order black-box nonlinear model is feasible, provided that identification or adaptivity is used for model tuning. The latter requirement is a result of a study of the robustness. In summary, the paper indicates that significant improvements as compared to linear control can be obtained with the proposed strategy.

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