Multi-variable flatness-based control for an engine cooling system

In this paper, a nonlinear control-oriented model of the thermal behaviour of an engine cooling system for vehicles is presented. The volume flow of an electrically driven coolant pump and the angular velocity of a radiator-fan unit serve as control inputs in a flatness-based nonlinear control approach. A constrained control problem arises due to the given physical bounds on the actuator inputs. Based on the derived system representation, a flatness-based control is designed that allows for tracking of desired trajectories for the engine outlet temperature as well as the radiator outlet temperature. The control structure is implemented in a time-discretised form. Furthermore, a discrete-time Extended Kalman Filter (EKF) is employed which estimates unmeasurable heat flows affecting the system. An experimental analysis using both feasible trajectories and infeasible trajectories, leading to actuator saturation, highlights the effectiveness of the model-based control approach.