Prioritization-based constrained trajectory planning for a nonlinear turbocharged air system with EGR

The problem of generating sufficiently smooth reference trajectories for the flatness-based feedforward control of a Diesel engine air system with input constraints is addressed in this work. The proposed trajectory planning can handle arbitrary command inputs and provides the reference signals required by the flatness-based controller. Thereby, the desired tracking behavior for the controlled variables is defined by a linear target system. The input constraints are taken into account by limiting the target system dynamics to the realizable air system dynamics as determined by the flat design model and the limits of the control input. Furthermore, a prioritization of the controlled variables is included in this limitation. The differentially flat reduced-order design model used in this work is deduced from a high-order reference model by applying the singular perturbation theory. The suitability of the proposed trajectory planning in combination with the feedforward controller is shown by means of simulation studies relying on the high-order reference air system model.