Research Of SCR Model Predictive Control Based On Rapid Prototype

In order to deal with the pollution caused by NO_x emissions emitted from ships,the International Maritime Organization has formulated strict legislations to limit NO_x emissions.Selective catalytic reduction technology is one of the most effective off-board emission reduction method,and the control of the urea injection quantity will directly affect the performance of the SCR system.This paper focuses on the control strategy of SCR system and carries out the following research:Firstly,mechanism of SCR reactions on vanadia-based catalyst is analyzed.According to the reaction rate equations of main reaction processes,the control-oriented model of single SCR catalyst is developed,containing the 3-state reaction kinetics model and 2-state thermodynamic model.Based on nonlinear least square method,the unknown parameters of the SCR models are identified.The parameter identification results show that the predicted values match well with the measured values from bench test,proving the high accuracy of the control-oriented SCR modelSecondly,the observer of the SCR system is developed based on Kalman filter algorithm.The observers of thermodynamic model and reaction kinetics model can estimate the state variables(exhaust temperature,catalyst temperature,NO_x concentration,NH₃ concentration and ammonia coverage ratio)inside SCR catalyst.The accuracy of the observers is verified by simulation under cyclic conditions.It shows that the estimated values of the observer can quickly converge to the model simulation values,and the error analysis proves that the state observer based on Kalman filter has high accuracy,which can be used in the research of SCR control strategy.Then,the predictive control strategy based on state space model of SCR system is established.The SCR state prediction equation is given in discrete form.Taking the catalyst ammonia coverage ratio as the control object,the ammonia coverage ratio is kept within a certain range to achieve the goal that the NH₃ slip does not exceed 10ppm and the NO_x conversion efficiency is maximized.The performance of the controller is preliminarily verified through simulation experiments under steady-state condition and cyclic condition.Finally,the rapid control prototype platform for the SCR system based on the d SPACE real-time simulation platform is established.The d SPACE hardware platform is taken as the controller to control the real SCR system.Experiments are carried out under steady-state condition and cyclic condition.The results show that the control strategy can quickly respond to external disturbances and changes of the control target,so that the ammonia coverage is well controlled within the target range.While the ammonia slip does not exceed 10ppm,it achieves high NO_x conversion efficiency.