Yanchao Sun

Adaptive neural network tracking control for multiple uncertain Euler–Lagrange systems with communication delays

Abstract This paper considers the distributed coordinated tracking control problems for multiple Euler–Lagrange systems with nonlinear uncertainties, external disturbances, and communication delays under the directed graph. First, distributed observers are designed such that all the followers can obtain the state information of the dynamic leader. Then, based on neural network and backstepping techniques, three distributed adaptive coordinated control algorithms are proposed to ensure that the tracking errors for each follower can be bounded. Compared with the first algorithm, the second algorithm guarantees the higher leader-following control accuracy. The third algorithm solves the chattering problem caused by discontinuous functions in the second algorithm. The closed-loop systems are investigated using the graph theory, Lyapunov theory, and Barbalat lemma. Finally, numerical examples and comparisons are provided to show the effectiveness and the performance of the proposed methods.

Distributed finite-time configuration containment control for satellite formation

This paper investigates the distributed finite-time configuration containment control problem for satellite formation with multiple leader satellites under directed communication topology. We consider that only a portion of follower satellites can receive leaders’ information and unknown perturbations and model uncertainties exist in the dynamics models of satellites. By defining the relative configuration error functions and selecting suitable nonsingular terminal sliding mode variables, a fully distributed finite-time configuration containment control scheme is proposed using the matrix properties of graph theory. The Lyapunov method is used to demonstrate the finite-time convergence property of the closed-loop systems. Numerical examples and comparisons with other methods are provided to show the effectiveness and the performance of the proposed control strategy.

Distributed finite-time coordinated control for multi-robot systems

In this paper, we study the finite-time coordinated control problems under directed topologies for multi-robot systems with general disturbances. The dynamics model of each robot is described by a Euler–Lagrange equation. When considering that only a subset of the follower robots has access to the leader information, the distributed finite-time tracking algorithm with an active leader robot is proposed. Then, we extend the tracking method to the case of containment control. Some special error functions and terminal sliding variables are defined. The finite-time convergence properties of the closed-loop systems are investigated by using a combination of matrix properties of graph theory and Lyapunov theory. Numerical examples and comparisons with other methods are provided to show the effectiveness and the performance of the proposed control strategies.

Neural network-based distributed adaptive configuration containment control for satellite formations:

Considering unknown perturbations and model uncertainties, this paper investigates the configuration containment control for satellite formations based on directed communication topologies. We consider that there are multiple leader satellites with constant relative velocities, while only a subset of follower satellites have access to the leaders. First, a distributed velocity observer is proposed for each follower to obtain velocity information of the leaders. Then, a distributed adaptive configuration containment control algorithm is proposed in which the model nonlinear uncertainties are approximated and compensated through neural networks, while the perturbations and approximation errors are compensated by adaptive gain technique. Furthermore, subject to the chattering caused by sign functions, an improved continuous containment strategy is developed. We use graph theory, Lyapunov theory, and Barbalat lemma to demonstrate that both proposed methods can make all the follower satellites converge to the convex hull spanned by the leader satellites. Numerical examples and comparisons are provided to show the effectiveness and performances of the proposed control strategies.

Distributed sliding-mode tracking control for multiple mechanical systems

Based on the sliding-mode and adaptive control theories, the distributed consensus tracking problem under directed topology is investigated for multiple mechanical systems in the presence of general disturbances. We consider that only a subset of the follower mechanical systems can get the information from the dynamic leader mechanical system. First, with the upper bounds of the general disturbances and the leader’s acceleration, a distributed sliding-mode tracking scheme is proposed. Then, when considering the high conservation of sliding-mode control, an improved algorithm with adaptation laws for the upper bounds is developed. Both the proposed algorithms can make tracking errors for each follower mechanical system asymptotically stable. Numerical examples and comparisons are provided to show the effectiveness and the performance of the proposed control strategies.

On Spacecraft Relative Orbital Motion Based on Main-Flying Direction Method

This paper introduces an analysis of a relative orbit control problem that how to let the tracking spacecraft be in the range of a small angle which is outward from the non-cooperative target spacecraft’s field of view, and at the same time satisfy the requirement of flight time and distance. This analysis is called “main-flying direction” analysis method. Based on this method, we provide a design method of the relative orbit in the fluttering mode that the tracking spacecraft flies in its own orbit after it enters into the spatial range relevant to the target spacecraft. This design method of solving the relative orbit control problem is demonstrated by simulations. The analysis thought and the calculation of this method are simple, and it avoids some disadvantages in other methods, such as the direction limitation of the field of view, attitude and orbit control coupling, etc.

Simple model-free attitude control design for flexible spacecraft with prescribed performance

In this paper, a model-free attitude control approach is proposed for the spacecraft in the presence of external disturbances and flexible vibrations with both complexity and performance concerns. By utilizing prescribed performance and backstepping techniques, the controller is constructed in a simple form without requiring any relevant information of the attitude control system dynamics. Moreover, fuzzy/neural network approximations, observers, or adaptive laws are not adopted into the control design, so that the related problems introduced by these estimation structures can be avoided. Numerical simulations in different cases show that the control system can obtain quick and smooth dynamic process and expected tracking accuracy despite the influence of disturbances and flexible vibrations, which demonstrates the effectiveness of the proposed scheme. Owing to the above good features, it is suitable for practical engineering.

Fixed-time nonsingular terminal sliding mode control for spacecraft rendezvous

This paper presents a fixed-time nonsingular terminal sliding mode control methodology for spacecraft rendezvous in the presence of nonlinearity and external disturbance. A nonsingular terminal sliding surface is constructed and a continuous sinusoidal function is introduced into the controller to solve the inherent singularity problem. Under the proposed controller, the relative position of the chaser spacecraft can rendezvous with the target within fixed time, which is demonstrated by Lyapunov theorem. The simulation results show that the proposed controller enables rapid convergence rate, high precision and strong robustness in the presence of nonlinearity and external disturbance.

Distributed coordinated attitude tracking control for spacecraft formation based on neural networks

This paper investigates the distributed attitude tracking control problem of spacecraft formation under a directed communication topology. A distributed coordinated attitude tracking control law based on neural networks is introduced to deal with the uncertainties and external disturbances when the time-varying leaders trajectory is available to only a subset of follower spacecraft. A Lyapunov analysis guarantees the convergence of attitude tracking errors to an arbitrarily small domain. Simulation results demonstrate the effectiveness of the proposed controller.

Adaptive finite-time control for spacecraft to track and point non-cooperative space targets

In this paper, we investigate the problem of tracking and pointing on-orbit non-cooperative targets. We establish the orbit and attitude dynamics equations between tracking spacecraft and non-cooperative targets in line-of-sight and body-fixed coordinate systems. Moreover, considering the bounded inputs of spacecraft, we propose the adaptive finite-time tracking and pointing control algorithm, which achieves finite-time stability of the closed-loop systems. Numerical simulation is given to illustrate the effectiveness of the proposed method.