Adaptive Feedforward Compensator Based on Approximated Causal Transfer Function for CACC with Communication Delay

Abstract

In this paper, we propose an adaptive feedforward compensator using parameter estimation to compensate for the communication time delay in cooperative adaptive cruise control (CACC). When CACC uses a feedforward controller to improve tracking performance and satisfy the string stability, it should take into account the communication delay between vehicles. Padé approximation of the time delay can be used for the design of feedforward compensator, but there is a limitation since the approximated system becomes the non-minimum system. To cope with this inherent non-causality problem, we propose an approximated causal transfer function for the feedforward compensator. Then, we apply extended Kalman filter as one of parameter estimation methods with a nonlinear model from the state augmented by a parameter of the approximated causal transfer function. Numerical simulation results show that the proposed system not only mitigates spacing error in time-varying communication delay but also satisfies string stability in a platoon.