Design of extended Kalman filter observer coupled to ammonia cross-sensitivity model for an SCR system

Commercial diesel vehicles that comply the China/EURO VI emission regulations are generally equipped with selective catalytic reduction (SCR) systems for reducing NOx emission and NOx sensors at its downstream for accurate closed-loop control. However, NOx sensors have significant ammonia cross-sensitivity pushing up their readings. Moreover, for the closed-loop control of SCR systems effectively estimating the critical states from the NOx sensor readings remains a further challenge. In this paper, an ammonia cross-sensitivity model with segmented sin and quadratic composite func-tions describing high frequency characteristics is established by analyzing the experimental data of an SCR system. A control-oriented three-states model of an SCR system is established, and based on it an extended Kalman filter (EKF) observer coupled to the ammonia cross-sensitivity model is proposed. The simulation results show that from the NOx sensor readings the EKF observer can effectively estimate the deterioration trend of the NOx and NH3 emissions, and describe the dynamic change process of the ammonia coverage rate. The experimental results under the four non -excitation cycles show that the EKF observer can effectively estimate the deterioration trend, that the average estimated accuracy of NH3 and NOx during their deterioration stage can respectively reach 86.16% and 54.87%, and that the observer has better robustness to disturbances from the operating conditions.

Automated summary

In this study, an ammonia cross-sensitivity model and a control-oriented three-states model of SCR system are established to effectively estimate the deterioration trend of NOx and NH3 emissions. The proposed EKF observer demonstrates good performance in estimating the critical states and is robust to disturbances from operating conditions.