A nonlinear switched observer with projected state estimates for diesel engine emissions reduction

This paper presents an exponentially converging nonlinear switched observer for diesel selective catalytic reduction (SCR) nitrogen oxide (NO
_x
) aftertreatment systems using only NO
_x
measurements. The state of the SCR system is shown to evolve in a physically meaningful positively invariant set. A state estimator is designed using a continuous-time observer, a switching law, and a projection that ensures the estimates are in the positively invariant set. The convergence rate of the estimates to the SCR states has the same bound as the corresponding continuous-time observer.