What is the Best Way to Optimally Parameterize the MPC Cost Function for Vehicle Guidance?

TL;DR

This paper compares different multi-objective optimization algorithms for tuning MPC parameters in autonomous vehicle control, focusing on sample efficiency and handling simulation crashes.

Contribution

It introduces adaptive batch size and crash constraint handling methods for Bayesian optimization, and evaluates their effectiveness in MPC parameter tuning.

Findings

Bayesian optimization performs best with small budgets.

NSGA-II is most effective with medium budgets.

For large budgets, random search is comparable to advanced methods.

Abstract

Model predictive control (MPC) is a promising approach for the lateral and longitudinal control of autonomous vehicles. However, the parameterization of the MPC with respect to high-level requirements such as passenger comfort as well as lateral and longitudinal tracking is a challenging task. Numerous tuning parameters as well as conflicting requirements need to be considered. This contribution formulates the MPC tuning task as a multi-objective optimization problem. Solving it is challenging for two reasons: First, MPC-parameterizations are evaluated on an computationally expensive simulation environment. As a result, the used optimization algorithm needs to be as sampleefficient as possible. Second, for some poor parameterizations the simulation cannot be completed and therefore useful objective function values are not available (learning with crash constraints). In this contribution, we compare the sample efficiency of multi-objective particle swarm optimization (MOPSO), a genetic algorithm (NSGA-II) and multiple versions of Bayesian optimization (BO). We extend BO, by introducing an adaptive batch size to limit the computational overhead and by a method on how to deal with crash constraints. Results show, that BO works best for a small budget, NSGA-II is best for medium budgets and for large budgets none of the evaluated optimizers is superior to random search. Both proposed BO extensions are shown to be beneficial.