Robust Control of Vehicle Platoons Based on a Unified Spacing Policy

We propose a robust control method for vehicle platoons based on a unified spacing policy, which can be customized for different vehicles within the platoon. This spacing policy integrates the constant time headway (CTH) and constant spacing (CS) policies into a single framework with some modifications. The policy can be adjusted to resemble either a CTH-like or CS-like approach by simply tuning a weighting factor for each vehicle. To increase road throughput, the velocity difference between the current vehicle’s velocity and the preceding vehicle’s low-pass filtered velocity is introduced to the proposed policy. A second-order low-pass filter is used for the preceding vehicle’s velocity. As a result, the sliding variable for each vehicle’s spacing error only requires the current vehicle’s position, velocity, acceleration, and the preceding vehicle’s position and velocity, all of which can be measured by onboard sensors. This design reduces the platoon’s reliance on inter-vehicle communication. A predefined-time modification is introduced to eliminate nonzero initial conditions in spacing and velocity errors, thereby improving transient performance. The local controller for each vehicle is based on a third-order nonlinear system model that accounts for nonlinear disturbances and engine lag. A smoothed sliding mode robust controller is then designed for each vehicle to stabilize its spacing error. The input-to-state stability (ISS) property of the spacing error is established through rigorous theoretical analysis. Furthermore, we demonstrate the practical strong frequency domain string stability (PSFSS) of the entire vehicle platoon, focusing on signal oscillations along the platoon. Finally, extensive numerical studies are conducted to demonstrate the effectiveness of the proposed method.