A Passivity Approach to String Stability and Distributed Adaptive Control of Vehicle Platoons

We study platoon control of autonomous electric vehicles. The dynamic model of such vehicle systems is inherently nonlinear, and involves unknown and uncertain parameters due to wear-tear, ageing, and changes of road conditions and surrounding environments. A distributed direct adaptive control law, resemble to the MIT rule, is employed to control the vehicles' longitudinal motion, globally asymptotically stabilizing the operating point, specified by the speed limit. More importantly, a passivity approach is adopted to analyze the disturbance string stability associated with the platoon of adaptive closed-loop vehicle control systems. It is shown that the distributed direct adaptive control law achieves the string stability in the presence of model nonlinearities and parameter uncertainties against the worst-case energy bounded disturbances without known bounds. Further analysis shows that the vehicle platoon under the distributed direct adaptive control law is capable of synchronizing all velocities while maintaining the required safe inter-vehicle distances. The results are illustrated by simulation studies compared with other existing methods for platoon control.