Communication delay compensation method of CACC platooning system based on model predictive control

The model predictive control (MPC) and long short term memory (LSTM) methods were used to mitigate the impact of communication delay on the cooperative adaptive cruise control (CACC) platooning system. A communication delay compensation method was proposed to guarantee the string stability of the CACC platooning system. A system framework was designed including vehicle dynamics model, spacing strategy, information topology and MPC controller. Moreover, a quantitative indicator of the string stability was proposed by considering 2 norm and infinite norm conditions. Consequently, a modeling and evaluation methodology of the CACC platooning system was constructed. A MPC method was proposed to take the preceding vehicle acceleration trajectory (PVAT) of the preceding vehicle as reference trajectory, namely MPC-PVAT. The following, traffic safety, traffic efficiency and fuel consumption were considered comprehensively. An objective function was minimized to construct the optimal control. The Pontryagin maximum principle was used to efficiently solve the optimization problem. Furthermore, a long short term memory network was used on the MPC-PVAT. The PVAT was replaced by the predicted result in the MPC of the preceding vehicle. The MPC-PVAT was upgraded to the MPC-LSTM. Therefore, the effect of communication delay was further mitigated. Simulation results show that the upper bound of communication delay is more than 1.5 s by using the MPC-LSTM, and improves by 0.8 and 1.1 s compared with the MPC-PVAT and linear controller, respectively. For the field test results, when the communication delay is 1.2 s, the quantitative indicator of the string stability of the MPC-LSTM improves by 20.33% and 39.35% compared with the MPC-PVAT and linear controller, respectively. Consequently, the MPC-LSTM can guarantee the string stability of a CACC platooning system while the effect of communication delay is well tolerated.