Hierarchical control of cooperative adaptive cruise control under communication and actuator delays

The cooperative adaptive cruise control (CACC) system is pivotal in improving traffic safety and efficiency by maintaining precise inter-vehicle gaps and regulating speed. However, communication and actuator delays often coexist and significantly affect the stability and operational safety of vehicle platoon systems. Although extensive research has been conducted on both types of delays, most studies have constructed and analyzed each delay independently, lacking a unified mitigation strategy for their combined effects. Therefore, this study introduces a novel distributed hierarchical control architecture that integrates upper-level decision-making with lower-level execution control. The upper-level controller employs a model predictive control (MPC) architecture enhanced by an adaptive Kalman filter (AKF) to mitigate state discrepancies caused by communication delays in car-following scenarios. This AKF-MPC controller further improves the real-time estimation of surrounding vehicle states, resulting in a more accurate desired acceleration. A Proportional-Integral-Derivative (PID) feedback controller is implemented at the lower level to track the desired acceleration from the upper-level controller, simultaneously compensating for actuator delays and enhancing closed-loop vehicle performance. The proposed architecture is validated through comprehensive simulations under diverse traffic conditions, demonstrating its effectiveness in significantly improving CACC system stability and safety under communication and actuator delays. This study can contribute to establishing a unified control architecture for cooperative vehicle systems, thereby providing a theoretical foundation for deploying delay-resilient CACC in intelligent transportation systems with heterogeneous communication constraints.