Modeling and Control of Diesel Engine Air Systems

This text deals with the control of turbocharged Diesel engine air systems with exhaust-gas recirculation. A novel prioritizing internal model control scheme systematically accounting for input constraints stemming from the physical limitations of the available air system control valves is proposed. The control design basically follows the classical design procedure: First, high-order models of the considered air systems are derived based on first principles. These full-order models are used as a reference for the evaluation of reduced-order models and controllers, and serve as a starting point for the control design. Reduced-order models suitable for model-based control design are deduced from the full-order models by employing the singular perturbation theory, where a number of simplifying assumptions render the resulting reduced-order models differentially flat. The flatness property of the reduced-order models is exploited for the design of feedforward controllers. Furthermore, in order to account for input constraints, a novel constrained trajectory planning is proposed. It guarantees that the input constraints are respected and further allows for the prioritization of certain controlled variables. The prioritizing internal model control scheme is finally obtained by interconnecting a flatness-based FF controller and a constrained trajectory planning. Simulation studies show that an excellent closed-loop performance is achieved for both a one-stage and a two-stage turbocharged air system with exhaust-gas recirculation.