Multi Reference Model Predictive EGR-Valve Control for Diesel Engines

Accurate control of the engine air system is essential to comply with emission legislation. Typically the real emission targets, like NOx, cannot be measured directly at a production car and thus different intermediate candidates, like gas mass flows or oxygen concentrations, are used. In general the candidate choice is a key factor for emissions, because each of them can only be determined with certain accuracy and consequently a feedback control based on a specific quantity is only capable of reaching a point within the accuracy range. Moreover, a sligh tdeviation of on ecandidate may, due to the nonlinear relations between emissions and candidates, lead to high NOx deviations. In a previous work four candidates for EGR valve control were analyzed and a scheduling scheme according to their NOx tracking performance under uncertainties was proposed. Within this work the approach is extended by the application of a multireference online MPC control strategy which takes also dynamical properties into account. To this end a scheduling between the candidates based on the static and dynamic analysis in the previous work is applied, where the idea is to adapt the inherited objective function during run time. The proposed dynamic reference scheduling strategy was implemented on a simulation model of a passenger car Diesel engine and satisfying results were obtained.