About string stability of a vehicle chain with unidirectional controller

TL;DR

This paper investigates the limitations and possibilities of achieving string stability in vehicle chains with unidirectional control, demonstrating that integral control can attain stronger stability properties.

Contribution

It extends the understanding of string stability limitations and shows that infinite steady-state gain via integral control can achieve stronger stability in vehicle chains.

Findings

Linear controllers cannot achieve string stability with relative distance inputs.

Adding absolute velocity measurements allows weaker string stability.

Infinite steady-state gain enables stronger string stability with integral control.

Abstract

This paper deals with the problem of string stability in a chain of acceleration-controlled vehicles. It is known that string stability cannot be achieved, with any linear controller, when the vehicles' control inputs are based on relative distances to a fixed number of predecessors. We extend the set of impossible settings by including elements like dynamic sensor parts and local inter-vehicular communication, as in cooperative adaptive cruise control. It is also known that a weaker form of string stability is achievable by adding absolute velocity measurements (e.g. "time-headway" policy). We show that a stronger property can also be achieved, provided steady-state control gain is infinite e.g. by using integral control.