String-stable constant-spacing platoons without communication

Abstract

This work considers string instability in constant-spacing-policy (CSP) platoons without communication. It is well known that platoons will have string instability without communication with CSP if the vehicle dynamics has at least two poles at the origin. This work considers a modification of the vehicle dynamics, using input-output feedback linearization along with stable-pole zero cancellations, to retain only one pole at the origin. As a result, it is possible to design CSP that is string stable without communication. A disadvantage, with the reduction to only one pole at the origin, is that there is non-zero steady-state error for a constant platoon-speed. However, it is shown that a Taylor-approximation-based, delayed-self-reinforcement (Taylor-approximated DSR) approach can substantially reduce the overall (transient and steady-state) spacing errors while avoiding string instability. Comparative simulations using a benchmark vehicle model show that the proposed Taylor-approximated DSR can reduce the overall error substantially (by 95%) when compared to the standard predecessor-following CSP platoons. Moreover, the resulting steady-state spacing deviation is more than 2 orders of magnitude less when compared to other string-stable approaches such as the constant-time-headway (CTH) policy.