Variable time headway spacing strategy for connected vehicles platoon based on sliding mode control

In complex traffic environments, the preceding vehicle in the platoon often experiences frequent acceleration and deceleration due to changing traffic conditions, resulting in fluctuations in the velocity of the following vehicles. While the current spacing strategy can help the platoon regain a stable state during the fluctuation of vehicle flow, it does not effectively suppress the velocity and acceleration fluctuations of the following vehicles during the adjustment process. This paper proposes a novel variable time headway (VTH) spacing strategy, which employs the neighboring vehicle velocity ratio to depict the relative variations in velocity and considers the impact of the preceding vehicle's acceleration. As a result, the fluctuations of the preceding vehicle can be precisely characterized allowing the following vehicles to respond promptly and accurately to the changes in the behavior of the preceding vehicle. Simultaneously, a robust low communication dependency (RLCD) system based on the third-order dynamic model is proposed to mitigate the impact of complexity and reliability of information flow topology (IFT) on platoon stability in the Vehicular Ad hoc NETwork (VANET). Based on the proposed VTH strategy, a robust coupled sliding mode controller for the platoon is designed under the low communication dependency requirement. Furthermore, by introducing dynamic sliding mode control into the coupled sliding mode surface, a smoother controller input is obtained while ensuring the string stability of the vehicle platoon. The numerical simulation results demonstrate conclusively that the proposed strategy effectively reduces velocity tracking errors and acceleration fluctuations for connected vehicles (CVs) in complex traffic environments. The fluctuations of the preceding vehicles can be more effectively absorbed, and the overall tracking performance of the vehicle platoon is enhanced.