Nonlinear Observer Design of Diesel Engine Selective Catalytic Reduction Systems With $\hbox{NO}_{x}$ Sensor Measurements

In this paper, we investigate the observer design problem of diesel engine selective catalytic reduction (SCR) systems. Considering the main chemical reactions, the SCR systems are modeled by assuming that the states are homogenous inside and SCR cells as continuous stirred tank reactors. The obtained system model is nonlinear and the states are coupled. Since the ammonia coverage ratio is not measurable by a physical sensor and the ammonia sensor is relatively costly, NO
_x
sensors are used to estimate the system states. The observability of the system is analyzed under the framework of the linear parameter-varying (LPV) system via transforming the nonlinear SCR system into a quasi-LPV form. A nonlinear observer is proposed and the method of tuning the observer gains is developed. The stability of the estimation error system is guaranteed with the designed observer gains. Finally, an experimental test with various operating points is conducted to show the effectiveness of the designed observer. It infers from the results that the designed observer has a good performance and the states are estimated well.