A smooth attitude-stabilizing control law is derived from which known limits on the control authority of the system are rigorously enforced. Unknown disturbance torques, assumed to be of lesser magnitude than the control limits, are included in the formulation. A smooth control signal containing hyperbolic tangent functions that rigorously obeys a known maximum-torque constraint is introduced. The controller can be viewed as a smooth analog of the variable-structure approach, with the degree of sharpness of the control permitted to vary with time according to a set of user-defined parameters. Lyapunov analysis is employed to ensure global stability, and asymptotic convergence of the angular velocity is guaranteed via the Barbalat lemma. Attitude errors, expressed as Euler parameters, are shown via simulation to vanish whenever certain design parameters are selected appropriately, and guidelines for selection of those parameters are provided in depth.

Globally stabilizing saturated attitude control in the presence of bounded unknown disturbances

Fixed-time neural network trajectory tracking control for underactuated surface vessels

A disturbance observer based intelligent control for nonstrict-feedback nonlinear systems

This article investigates the distributed event‐triggered affine formation maneuver control problem for multiple underactuated surface vessel (USV) systems with positive minimum inter‐event times (MIET). Unlike common formation control methods that only ensure the formation system to keep a fixed geometric shape, the proposed scheme enables multiple USVs maneuver as a group in translation, shearing, rotation, or combinations of them. The proposed control strategy is composed of two parts. First, a distributed event‐triggered observer (DETO) is proposed to observe the time‐varying target formation under the lack of global leaders' information and govern the inter‐vessel communications among the formation group. Besides, the MIET of the designed communication strategy is proved to be strictly positive and computable from formation configurations and control parameters. With these guarantees, the maximum communication frequency can be known in advance. Then, upon the DETO signals, the adaptive local tracking controller is subsequently synthesized for each vessel to realize the target formation track. Rigorous theoretical analysis and simulation results are finally conducted to verify the validness and effectiveness of the proposed algorithm.

Distributed observer based event‐triggered affine formation maneuver control for underactuated surface vessels with positive minimum inter‐event times

Finite-time time-varying formation control for marine surface vessels

Finite-time distributed formation control for multiple unmanned surface vehicles with input saturation

Minimum-learning-parameter-based anti-unwinding attitude tracking control for spacecraft with unknown inertia parameters

This brief disposes the finite-time anti-unwinding trajectory tracking control problem of the autonomous underwater vehicle (AUV) encountering model uncertainties, ocean disturbances and actuator failures. Primarily, the kinematic model of translational and rotational motions is depicted by unit quaternion in lieu of classical Euler angle such that the AUV's dynamics could be globally and uniquely formulated. Subsequently, two finite-time control strategies are presented here to leave the state variables of AUV can converge to an adjustable region. Additionally, the adaptive laws could be applicable to the existence of actuator faults by utilizing a passive fault-tolerant technology. By integrating the initial value of the scalar quaternion into the sliding mode surface, the proposed controllers are characterized with anti-unwinding property. Then, with the application of hyperbolic tangent function, finite-time stability will be achieved for tracking errors without singularity. Stability of the closed-loop system is verified via the Lyapunov theorem. Finally, numerical simulations are presented to demonstrate the effectiveness of the proposed controllers. 

Quaternion-based finite-time fault-tolerant trajectory tracking control for autonomous underwater vehicle without unwinding.

Prescribed performance-based robust inverse optimal control for spacecraft proximity operations with safety concern

This paper develops a distributed bearing-only method for the splitting and merging control of multiple underactuated autonomous surface vessels (ASVs) under GPS-denied and obstacle-cluttered environment. Most of the distributed results are implementable based on the assumption that the position of each ASV is accessible. However, it is somewhat idealistic since the loss of the communication network and GPS signals possibly occurs due to various interferences, like the same-band signals and intentional cyber attacks. To this end, a bearing-only formation splitting and merging method is presented in this context. With bearing constraint only, the ASV formation is able to maneuver in GPS-denied environment, while the formation splitting and merging strategy renders it possible for multiple ASVs to automatically resize and splitting when facing signal-blocking obstacles. Simulation results have revealed that the formation keeping and obstacle avoidance can be achieved upon using the proposed method, even with partial losses of the visual connections among ASV members.

Shuo Song

Papers

Finite-time distributed formation control for multiple unmanned surface vehicles with input saturation

Minimum-learning-parameter-based anti-unwinding attitude tracking control for spacecraft with unknown inertia parameters

Quaternion-based finite-time fault-tolerant trajectory tracking control for autonomous underwater vehicle without unwinding.

Prescribed performance-based robust inverse optimal control for spacecraft proximity operations with safety concern

Distributed Bearing-only Formation Splitting and Merging Control of Underactuated Autonomous Surface Vessels