SEAL: Safety Enhanced Trajectory Planning and Control Framework for Quadrotor Flight in Complex Environments

TL;DR

SEAL addresses safe autonomous quadrotor flight in wind-disturbed, dynamic environments by unifying planning and control. It combines a real-time, disturbance-aware planner based on forward reachable sets with ellipsoidal uncertainty bounds and a generalized PI observer for wind estimation, together with an NMPC tracker that compensates disturbances. The approach achieves proactive safety through FRS-propagated constraints, adaptive obstacle thresholds, and replanning in the presence of dynamic obstacles, demonstrated in both simulations and indoor real-world experiments. The results show improved tracking accuracy, higher success rates under challenging wind conditions, and robust handling of dynamic obstacles, enabling practical deployment in complex environments.

Abstract

For quadrotors, achieving safe and autonomous flight in complex environments with wind disturbances and dynamic obstacles still faces significant challenges. Most existing methods address wind disturbances in either trajectory planning or control, which may lead to hazardous situations during flight. The emergence of dynamic obstacles would further worsen the situation. Therefore, we propose an efficient and reliable framework for quadrotors that incorporates wind disturbance estimations during both the planning and control phases via a generalized proportional integral observer. First, we develop a real-time adaptive spatial-temporal trajectory planner that utilizes Hamilton-Jacobi (HJ) reachability analysis for error dynamics resulting from wind disturbances. By considering the forward reachability sets propagation on an Euclidean Signed Distance Field (ESDF) map, safety is guaranteed. Additionally, a Nonlinear Model Predictive Control (NMPC) controller considering wind disturbance compensation is implemented for robust trajectory tracking. Simulation and real-world experiments verify the effectiveness of our framework. The video and supplementary material will be available at https://github.com/Ma29-HIT/SEAL/.

Figures (9)

• Figure 1: Snapshot of an indoor real flight test. (a) The dynamic obstacle (in red dashed line) is moving towards the quadrotor, while the quadrotor enters the wind zone that pushes it towards the obstacles. Our planner replans a safe and feasible trajectory (in red line). (b) The visualization of the flight.
• Figure 2: The system overview diagram of SEAL. The disturbance observer provides an online estimation of wind forces while the planner and controller handle the disturbance jointly to generate a safe, smooth, and feasible trajectory and track it accurately.
• Figure 3: Collision-check and replanning mechanism.
• Figure 4: Quadrotor trajectory in X-Y plane under wind with average speed of $5m/s$.
• Figure 5: The tracking error of NMPC w/ and w/o disturbance observer.