Research On Model Based Temperature Control For Diesel Oxidation Catalyst(DOC)

As the requirements of emission regulations continue to increase,the role of engine exhaust after-treatment devices is increasingly important.At present,the structure of DOC+DPF+SCR is a mainstream scheme for emission regulations for heavy-duty diesel engines that exceed the national V emission standards.Among them,DOC is used to oxidize NO,CO,and HC in tail gas.The main role of DOC is to control DOC downstream through fuel injection.The outlet temperature enables active regeneration of the DPF.The active regeneration of the DPF has high requirements on the control of the DOC temperature.If the temperature is too low,active regeneration cannot be initiated,and if the temperature is too high,the DPF carrier may be damaged.Therefore,the precise control of DOC outlet temperature is of great significance.In this paper,the DOC temperature control method is studied in depth,and the dynamic characteristic model of the control-oriented DOC system is established.The accuracy of the model is verified by experiments.Based on the model,the PID and model predictive controller(MPC)closed-loop controllers were designed respectively.The simulation and control of different control methods were compared.Firstly,the mathematical model of the DOC was designed,and experimental calibration and verification were performed.Researched the modeling methods of DOC temperature field at home and abroad,analyzed and summarized the main physical and chemical processes that affected the temperature field of DOC,and used the basic principles of thermodynamics,fluid mechanics,heat transfer and chemical reaction dynamics to establish the bias of temperature field of DOC.Differential equation group mathematical description.To meet the requirements of control algorithm design,axial discretization of DOC temperature field description is simplified to a higher-order linear model with time delay.The obtained model was calibrated and verified by engine bench test.The results show that the model can accurately estimate the dynamic response characteristics of the outlet temperature downstream of the DOC.This model is used as a controlled object to study the design of a PID feedback controller for the downstream outlet temperature of the DOC.The impact of DOC delay on feedback control performance is analyzed.Based on Smith predictor,the traditional PID controller is improved and the influence of significant time-delay links on control performance is eliminated.The simulation model of the control system is set up,and the principle of eliminating the influence of the Smith predictor on the time delay is compared and analyzed.The DOC downstream outlet temperature MPC design was studied.According to the characteristics of the DOC system,the corresponding cost function and input and output constraints are determined.The simulation model of the DOC control system based on MPC is established.Through the analysis of the simulation results,the prediction step and control step of the reasonable MPC controller are determined.Fast and accurate DOC downstream temperature control.Finally,the difference between the performance of the PID and MPC controller at the outlet temperature control downstream of the DOC is compared.Based on the comparative analysis of control performance for different operating conditions,the robustness of unknown factors such as time-delay errors,time constant errors,and system external disturbances of the two controllers are analyzed separately.The simulation results show that under the condition of accurate parameters,the performance of the two controllers is similar,but in the case of variable operating conditions and inaccurate parameters,the PID controller is more sensitive to the model parameters,and the degradation of control performance is more significant,while the MPC control The device shows better robustness.