Adaptive Stochastic Nonlinear Model Predictive Control with Look-ahead Deep Reinforcement Learning for Autonomous Vehicle Motion Control

Propagating uncertainties through nonlinear system dynamics in the context of Stochastic Nonlinear Model Predictive Control (SNMPC) is challenging, especially for high-dimensional systems requiring real-time control and operating under time-variant uncertainties such as autonomous vehicles. In this work, we propose an Adaptive SNMPC (aSNMPC) driven by Deep Reinforcement Learning (DRL) to optimize uncertainty handling, constraints robustification, feasibility, and closed-loop performance. To this end, our SNMPC uses Polynomial Chaos Expansion (PCE) for efficient uncertainty propagation, limits its propagation time through an Uncertainty Propagation Horizon (UPH), and transforms nonlinear chance constraints into robustified deterministic ones. We conceive a DRL agent to proactively anticipate upcoming control tasks and to dynamically reduce conservatism by determining the most suitable constraints robustification factor κ, and to enhance feasibility by choosing optimal UPH length T_u. We analyze the trained DRL agent's decision-making process and highlight its ability to learn context-dependent optimal parameters. We showcase the enhanced robustness and feasibility of our DRL-driven aSNMPC through the real-time motion control task of an autonomous passenger vehicle when confronted with significant time-variant disturbances while achieving a minimum solution frequency of 110Hz. The code used in this research is publicly accessible as open-source software: https://github.com/bzarr/TUM-CONTROL