Event-Based Control of Freeway Systems

Objective of this paper is to define an innovative control scheme to reduce congestion in freeway traffic systems via ramp metering. Such a control scheme is event-based and is composed of two control levels. At the lower level, Model Predictive Control is applied: the cell transmission model, reformulated in the so-called mixed-logical dynamical form, is adopted as internal model for the prediction and the quadratic deviations of the system variables from specific set-points are used as objective function in the finite horizon optimal control problem. The higher level of the control scheme consists of a discrete-event supervisor capable of distinguishing between regular and specific traffic conditions, adjusting the control law accordingly. More precisely, on the occurrence of classified events, the discrete-event supervisor determines the most suitable control action by making the controller switch among the elements of a set of model predictive controllers based on different internal models and cost functions.