Trajectory generation for open/close gap maneuvers in vehicle strings

Cooperative adaptive cruise control (CACC) is an advanced technology allowing vehicle following at a small inter-vehicle spacing. In its classical usage, CACC assumes that vehicles are arranged in the form of a vehicle string and follow each other at a velocity-dependent distance. Nonetheless, practical driving situations include the case of lane changes, where vehicles can join or leave a vehicle string. In such case, it is required that gaps for joining vehicles are provided or gaps after leaving vehicles are closed in order to ensure safe and efficient driving. This thesis is concerned with gap opening and closing maneuvers in vehicle strings. Introducing a suitable control architecture, gap opening and closing maneuvers can be realized by the generation of feedforward input signals. To this end, the first contribution of the thesis is the development of five methods for the computation and representation of gap opening and closing trajectories that fulfill additional safety and comfort constraints. The first method is based on the solution of an optimal control problem, the second method uses a polynomial trajectory and plant inversion, the third method concatenates three polynomials and uses nonlinear programming to determine the polynomial coefficients, the fourth method uses a high-order polynomial and the fifth method uses concatenated polynomials in order to approximate the optimal control solution. A simulation study shows that the fifth method is particularly useful in practical applications since it computes trajectories that approximate the optimal control solution in real-time. The second contribution of the thesis is the implementation of a vehicle model that realizes CACC and additional feedforward signals in the form of a Matlab S-function.