Sliding mode observer for exhaust pressure estimation in light-duty diesel engines equipped with VGT and EGR system

Abstract

This paper proposes a nonlinear sliding mode observer for exhaust pressure estimation. A precise estimation of the exhaust pressure is important for the control of a variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR) system. In order to estimate the exhaust pressure accurately, we derive nonlinear dynamic models of the intake and exhaust pressure in diesel engines based on the energy and mass conservation laws. The model parameters which vary with the engine operating conditions are modeled through an empirical approach to consider physical phenomenon of each component. We develop the nonlinear sliding mode observer for the exhaust pressure estimation to deal with nonlinear dynamics of the diesel engine air system. The stability of the proposed observer is guaranteed by the Lyapunov stability criterion. Moreover, the estimation performance is improved by adding a damping term into the observer. The proposed observer is implemented in a real-time embedded system and the experimental results represent that the observer estimates exhaust pressure precisely in both steady and transient engine operating conditions.