  This paper investigates options to complement a diesel engine airpath
feedback controller with a feedforward. The control objective is to track the
intake manifold pressure and exhaust gas recirculation (EGR) rate targets by
manipulating the EGR valve and variable geometry turbine (VGT) while satisfying
state and input constraints. The feedback controller is based on rate-based
Model Predictive Control (MPC) that provides integral action for tracking. Two
options for the feedforward are considered one based on a look-up table that
specifies the feedforward as a function of engine speed and fuel injection
rate, and another one based on a (non-rate-based) MPC that generates dynamic
feedforward trajectories. The controllers are designed and verified using a
high-fidelity engine model in GT-Power and exploit a low-order rate-based
linear parameter-varying (LPV) model for prediction which is identified from
transient response data generated by the GT-Power model. It is shown that the
combination of feedforward and feedback MPC has the potential to improve the
performance and robustness of the control design. In particular, the feedback
MPC without feedforward can lose stability at low engine speeds, while
MPC-based feedforward results in the best transient response. Mechanisms by
which feedforward is able to assist in stabilization and improve performance
are discussed.
