  In this study, we propose a rotation-based connected automated vehicle (CAV)
distributed cooperative control strategy for an on-ramp merging scenario. By
assuming the mainline and ramp line are straight, we firstly design a virtual
rotation approach that transfers the merging problem to a virtual car following
(CF) problem to reduce the complexity and dimension of the cooperative CAVs
merging control. Based on this concept, a multiple-predecessor virtual CF model
and a unidirectional multi-leader communication topology are developed to
determine the longitudinal behavior of each CAV. Specifically, we exploit a
distributed feedback and feedforward longitudinal controller in preparation for
actively generating gaps for merging CAVs, reducing the voids caused by
merging, and ensuring safety and traffic efficiency during the process. To
ensure the disturbance attenuation property of this system, practical string
stability is mathematically proved for the virtual CF controllers to prohibit
the traffic oscillation amplification through the traffic stream. Moreover, as
a provision for extending the virtual CF application scenarios of any curvy
ramp geometry, we utilize a curvilinear coordinate to model the two-dimensional
merging control, and further design a local lateral controller based on an
extended linear-quadratic regulator to regulate the position deviation and
angular deviation of the lane centerlines. For the purpose of systematically
evaluating the control performance of the proposed methods, numerical
simulation experiments are conducted. As the results indicate, the proposed
controllers can actively reduce the void and meanwhile guarantee the damping of
traffic oscillations in the merging control area.
