Hierarchical predictive control for ground-vehicle maneuvering

Abstract

Abstract-This paper presents a hierarchical approach to feedback-based trajectory generation for improved vehicle autonomy. Hierarchical vehicle-control structures have been used before-for example, in electronic stability control systems, where a low-level control loop tracks high-level references. Here, the control structure includes a nonlinear vehicle model already at the high level to generate optimization-based references. A nonlinear model-predictive control (MPC) formulation, combined with a linearized MPC acting as a backup controller, tracks these references by allocating torque and steer commands. With this structure the two control layers have a physical coupling, which makes it easier for the low-level loop to track the references. Simulation results show improved performance over an approach based on linearized MPC, as well as feasibility for online implementations.

Symbolic elimination in dynamic optimization based on block-triangular ordering

“…The main idea of direct collo-cation is to discretize (11) by dividing the time horizon into a finite number of elements and then within each element approximate the system trajectories by polynomials defined by collocation points [14,15,45]. The result is a nonlinear program (NLP) whose solution approximates the solution of (11).…”

“…However, going all the way to an explicit ODE is not necessary when applying direct collocation in the context of dynamic optimization, as collocation methods are perfectly capable of dealing with low-index (and to some extent also high-index) implicit DAEs. In this section we describe how the causalization techniques can be applied to (11) to symbolically eliminate many of the algebraic variables.…”

“…However, (11) captures the essentials and the generalization of the presented methods to the wider class is straightforward, and so we restrict ourselves to (11) for the sake of brevity.…”

“…We mainly consider the use of direct collocation to solve (11). The main idea of direct collo-cation is to discretize (11) by dividing the time horizon into a finite number of elements and then within each element approximate the system trajectories by polynomials defined by collocation points [14,15,45].…”

“…Safdarnejad et. al [55] consider the use of BLT decompositions for the purpose of more efficiently generating initial guesses to (11) by solving square problems (with fixed degrees of freedom), and in particular identifying infeasibilities. They do however not consider BLT decompositions for the actual solution of (11).…”