Distributed nonlinear control for homogeneous vehicle platoons using Riemannian contraction metrics and control barrier functions

In this paper, a two-layer safety-critical controller for cooperative adaptive cruise control (CACC) of a platoon of vehicles governed by third-order nonlinear dynamics using Riemannian contraction metrics and control barrier functions (CBFs) is presented. The role of the first layer is to achieve exponential state synchronization of the vehicle platoon with a virtual leader exploiting a contraction metric. Since this implies collisions between the vehicles, the resulting control action is fed into an optimization problem derived from CBFs. The imposed constraints include a spacing constraint to guarantee safety and avoid collisions. The framework allows the inclusion of other constraints such as velocity constraints to respect road regulations, acceleration constraints to avoid unreasonable accelerations/ decelerations, and actuator constraints to comply with the vehicle physical limitations. The effectiveness of the suggested controller is subsequently validated through a simulation study.