EGR-VGT Control and Tuning for Pumping Work Minimization and Emission Control
A control structure is proposed and investigated for coordinated
control of exhaust gas recirculation (EGR) valve and variable
geometry turbochargers (VGT) position in heavy duty diesel
engines. Main control goals are to fulfill the legislated emission
levels, to reduce the fuel consumption, and to fulfill safe operation
of the turbocharger. These goals are achieved through regulation of
normalized oxygen/fuel ratio, $lambda_{O}$ , and intake manifold
EGR-fraction. These are chosen both as main performance variables and
feedback variables since they contain information about when it is
possible to decrease the fuel consumption by minimizing the pumping
work. Based on this a novel and simple pumping work minimization
strategy is developed. The proposed performance variables are also
strongly coupled to the emissions which makes it easier to adjust
set-points, e.g., depending on measured emissions during an emission
calibration process, since it is more straightforward than control of
manifold pressure and air mass flow. Further, internally the
controller is structured to handle the different control
objectives. Controller tuning is important for performance but can be
time consuming so the controller objectives are captured in a cost
function, which makes automatic tuning possible even though
objectives are conflicting. Performance tradeoffs are necessary and
are illustrated on the European Transient Cycle. The controller is
validated in an engine test cell, where it is experimentally
demonstrated that the controller achieves all the control objectives
and that the current production controller has at least 26% higher
pumping losses compared to the proposed controller.
Johan Wahlström, Lars Eriksson and Lars Nielsen
IEEE Transactions on Control Systems Technology,
2010
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