Distributed Robust Safety-Critical Predefined-Time Control for Target Spherical Surrounding of UAVs

This paper develops a distributed safety-critical predefined-time control method for the 3-dimensional (3D) moving target surrounding problem of multiple UAVs. A new 3D surrounding shape is first formulated for multiple UAVs to distribute on a moving spherical surface around the target. To reduce the communication and load burden, a predefined-time distributed estimator is designed for a subset of UAVs without any access to the target, so that the target's motion information can be accurately estimated within a predefined time. Subsequently, a robust safety-constrained predefined-time control law is designed with a twofold structure, where the nominal control term guarantees the predefined-time convergence under the safety constraints, and the adjunctive control term overcomes the influence of disturbances. A new dynamic parameter-based predefined-time control method is proposed, which can relax the unnecessary requirement of control design for achieving predefined-time convergence. The corresponding dynamic parameter-based predefined-time control Lyapunov function (DPP-CLF) is constructed together with second-order control barrier function (SCBF) to map the convergence requirement and safety constraints on states to constraints on control inputs. The nominal control term is obtained by minimizing the control inputs under constraints with linear programming. The adjunctive control term is acquired by combining a filter-based estimator and an integral sliding mode surface design, providing an accurate compensation for the disturbances. The theoretical analysis and simulation results demonstrate the predefined-time stability and collision avoidance performance of the multi-UAV system.