To improve the economy of vehicles in complex road environments

a hierarchical optimal control strategy is designed for vehicle platoon. Among them

the upper layer for complex roads containing curves

slopes and with speed limits

comprehensively considering the vehicle longitudinal and lateral dynamic characteristics on driving economy and safety

a variable-step rolling iterative dynamic planning method is proposed: firstly

the road is divided into stages on the distance domain according to the speed limit

and then on each stage through multiple iterations

gradually shrink the state volume and control volume grid for calculation to online rolling solution to obtain the economic speed trajectory of the head vehicle; the lower layer is based on model predictive control

constructing a multi-constraint system predictive model by queueing vehicle kinematic model and introducing a relaxation factor for softening

extending the solution feasible domain

and designing a following strategy for the back of the queue to achieve cooperative adaptive cruise control to follow the speed trajectory of the head vehicle. The simulation analysis shows that the proposed method in the upper layer has improved energy efficiency and computational efficiency compared with the traditional optimization method; the following strategy in the lower layer can effectively follow the speed trajectory of the head vehicle and shows good following performance.