Finite-time Disturbance Observer Research Articles

Adaptive hierarchical sliding mode controller for tower cranes based on finite time disturbance observer

SummaryA finite time disturbance observer (FTDO) based adaptive hierarchical sliding mode control (AHSMC) is proposed for 4‐DOF tower crane systems with unknown external disturbances. More specifically, to overcome the unknown disturbances, an FTDO combined with the designed adaptive observation error is presented to estimate both matched and unmatched disturbances. Then a new error dynamics taking into account the unmatched disturbances is defined, based on which, a novel nonsingular fast terminal sliding mode (FTSM) surfaces is designed to improve the convergence of system states. Finally, in order to ensure the stability of each subsystem, an AHSMC law incorporating the suggested FTSM‐type reaching law is presented to realize the anti‐sway and positioning control of tower crane system. The finite‐time stability analysis of the closed‐loop system is derived by Lyapunov technique, and simulation results verify the effectiveness of the presented control strategy.

Disturbance Observer-Based Finite-Time Control for Three-Phase AC–DC Converter

For three-phase ac–dc converters, load disturbances, and parameter uncertainties cause large fluctuations of the dc-link voltage, even resulting in system instability. In order to cope with this problem, the disturbance observer-based finite-time control (DOFTC) is put forward in this article, where the finite-time disturbance observer is designed to fast and accurately estimate disturbances. Subsequently, the stability of the ac–dc converter closed-loop system is analyzed and theoretically proved. Finally, experimental results verify the effectiveness of the DOFTC strategy, where good dynamic and steady-state performance is achieved under load disturbance and parameter uncertainties. Compared with the enhanced state observer-based sliding mode control and adaptive control method, the proposed DOFTC method not only reduced the fluctuations of the dc-link voltage by at least 55% but also improved the transient response.

Finite time trajectory tracking control of autonomous agricultural tractor integrated nonsingular fast terminal sliding mode and disturbance observer

A novel control strategy is proposed in this paper to improve the trajectory tracking performance of the autonomous agricultural tractor on both straight-line parallel tracks and headland turning curve tracks in the face of slippage, which combines the nonsingular fast terminal sliding mode (NFTSM) control with a kind of finite time disturbance observer (FDO). The designed FDO ensures robustness outside the sliding mode surface, while the constructed NFTSM ensures the fast convergence of tracking errors and chattering suppression. The effectiveness and advantages of the designed control strategy are verified by simulation comparison with the existing results under MATLAB/Simulink and CarSim co-simulation environment.

Disturbance rejection and performance enhancement of perturbed tri-stable energy harvesters by adaptive finite-time disturbance observer

Disturbance rejection and performance enhancement of perturbed tri-stable energy harvesters by adaptive finite-time disturbance observer

Composite SOSM controller for path tracking control of agricultural tractors subject to wheel slip

In the work, the path tracking control methods are developed for autonomous agricultural tractors subject to wheel slip constraints by using second-order sliding mode (SOSM) and finite-time disturbance observer (FDOB) techniques. First of all, the path tracking error dynamics derived from the kinematic model is given and applied to controller design. In order to deal with the inevitable chattering problem existing in the conventional first-order sliding mode (FOSM) controller, a SOSM controller is constructed by regarding the controller derivative as the new control law, which means that the practical control law can be seen as an integration of the SOSM controller. Through a combination of the FDOB and the designed SOSM controller, the composite path tracking controller is further constructed to avoid high control gains in the designed SOSM controller. The strict Lyapunov stability analysis is carried out to ensure that the sliding variable can be finite-time stabilized to the origin under the proposed control algorithms. Finally, the comparative simulation results confirm that the developed guidance laws can achieve good tracking performance and strong robustness even in the presence of slipping effects.

Finite-Time Distributed Leaderless Cooperative Guidance Law for Maneuvering Targets under Directed Topology without Numerical Singularities

A new distributed leaderless cooperative guidance algorithm is suggested for multi-directional saturation strikes against maneuvering targets. First, the finite-time disturbance observer (FDO) is used to estimate the target’s unknown maneuvers. After that, the guidance laws along the line-of-sight (LOS) direction and the LOS normal direction are designed separately based on the finite-time consensus theory. The proposed guidance law could satisfy both impact time and LOS angle constraints. Numerical singularities due to feedback linearization are avoided by nonlinear stability analysis. Finally, the effectiveness of the proposed cooperative guidance law is proved by numerical simulation arithmetic.

Finite time observer‐based super‐twisting sliding mode control for vehicle platoons with guaranteed strong string stability

This paper presents a finite time disturbance observer (FTDO)-based super-twisting sliding mode control (SMC) structure for a vehicle platoon system with a focus on parameter uncertainties as well as external disturbances. In order to compensate the parameter uncertainties and external disturbances, a composite FTDO-based super twisting SMC method is developed under zero initial spacing deviations, where the parameter uncertainties, external disturbances, and the preceding vehicle's acceleration are estimated as a lumped disturbance by employing an FTDO. Benefiting from the FTDO, the estimation error dynamics is stable in finite time. Different from the existing SMC-based achievements, the continuity of the control signals can be achieved, which avoids the undesirable chattering phenomenon in the existing SMC-based works. Leveraging an FTDO, the preceding vehicle's acceleration information is not required, which enables the proposed control method to exploit a unidirectional information flow topology. Thus, it can reduce communication burden compared with bidirectional information flow topologies. Then, an improved time gap policy is employed to extend the developed control scheme to a more general case with nonzero initial spacing deviations. In addition, the individual stability of each vehicle is rigorously analyzed by resorting to the Lyapunov stability theory. Furthermore, the strong string stability of the whole vehicle platoon is derived with the help of the Laplace transform. Finally, numerical simulations are conducted to illustrate the effectiveness and applicability of the developed control scheme.

Global finite‐time cooperative control for multiple manipulators using integral sliding mode control

AbstractIn this paper, a global finite‐time cooperative control is first time proposed for cooperative multiple manipulators. The proposed control scheme is developed based on an integration between a finite‐time disturbance observer (FTDO) and a finite‐time integral sliding mode controller (FTISMC) to get a high robustness against the effects of the model uncertainties and disturbances in the system. The switching term of the integral sliding mode controller is reconstructed such that the desired sliding manifold can be convergent in a finite time. The nominal controller of the integral sliding mode control is developed based on an advanced backstepping control, namely, finite‐time backstepping control, which also provides a finite time convergence. The integration of the finite‐time disturbance observer, finite‐time switching term, and the finite‐time backstepping controller forms a new global finite‐time integral sliding mode control. The effectiveness of the proposed approach is demonstrated based on a cooperative control of a dual two‐link manipulators.

SLIDING MODE CONTROL OF UNMANNED AERIAL VEHICLE BASED FINITE-TIME DISTURBANCE OBSERVER

Because of the advantages of high maneuverability, vertical takeoff and landing, free hovering, and easy portability, quadrotor UAVs have become one of the research hotspots in recent years. Aiming at the finite-time trajectory tracking control problem for quadrotor under unknown environmental disturbance and modeling uncertainty, a fast terminal sliding mode control method using a finite-time disturbance observer is proposed. First, the modeling uncertainty and unknown external disturbance of the quadrotor were combined into lumped disturbance, and a finite-time disturbance observer was designed to estimate the lumped disturbance online. Secondly, a fast terminal sliding mode controller was constructed for the realization of a finite-time tracking control of the quadrotor, and the estimated value of the limited-time disturbance observer was compensated to the controller. Thereby, the influence of compound disturbance was eliminated, the quadrotor can achieve a finite-time trajectory, and the disturbance suppression capability of tracking control was improved. Finally, we conducted simulation experiments and confirmed that the control strategy proposed in this paper is effective.

Finite-time composite control for gimbal system in SGCMG under high-frequency disturbance

This paper investigates the velocity-tracking problem of the gimbal system in a single gimbal control moment gyro (SGCMG) suffering from high-frequency disturbance. In order to accurately and quickly reject the high-frequency disturbance resulted from nonuniform mass distribution and manufacturing imperfection, a finite-time harmonic disturbance observer (FTHDO) is constructed according to the available information about the high-frequency disturbance. Then, a composite controller is developed to achieve simultaneous disturbance rejection and attenuation. The nominal control performance can be recovered under the high-frequency disturbance. It has been demonstrated that the velocity-tracking error can be stabilized by the proposed composite controller within finite time. Finally, numerical simulation results are presented to verify the superiority of the proposed method.

Three-agent Time-constrained Cooperative Pursuit-Evasion

This paper considers a pursuit-evasion scenario among three agents– an evader, a pursuer, and a defender. We design cooperative guidance laws for the evader and the defender team to safeguard the evader from an attacking pursuer. Unlike differential games, optimal control formulations, and other heuristic methods, we propose a novel perspective on designing effective nonlinear feedback control laws for the evader-defender team using a time-constrained guidance approach. The evader lures the pursuer on the collision course by offering itself as bait. At the same time, the defender protects the evader from the pursuer by exercising control over the engagement duration. Depending on the nature of the mission, the defender may choose to take an aggressive or defensive stance. Such consideration widens the applicability of the proposed methods in various three-agent motion planning scenarios such as aircraft defense, asset guarding, search and rescue, surveillance, and secure transportation. We use a fixed-time sliding mode control strategy to design the control laws for the evader-defender team and a nonlinear finite-time disturbance observer to estimate the pursuer’s maneuver. Finally, we present simulations to demonstrate favorable performance under various engagement geometries, thus vindicating the efficacy of the proposed designs.

Neuro-adaptive containment control of unmanned surface vehicles with disturbance observer and collision-free

The adaptive containment control problem with collision avoidance is investigated for unmanned surface vehicles (USVs). At first, the finite time disturbance observer is developed to present the estimation and compensation of external disturbance. Then, incorporating the artificial potential and radial basis function into the new containment strategy, all followers can enter the convex hull spanned by leaders while the collision is avoided. Furthermore, it is demonstrated that the error signals in the closed-loop system are boundedness by employing Lyapunov stability. Simulation studies finally manifest the effectiveness of proposed method.

A Hybrid Autonomous Recovery Scheme for AUV Based Dubins Path and Non-Singular Terminal Sliding Mode Control Method

In order to improve the persistent operation capacity of autonomous underwater vehicle (AUV), autonomous recovery system draws more and more attention in recent years. A hybrid scheme combined with navigation, guidance and control is proposed to complete the function of autonomous recov-ery of AUV in the paper. Based on the hybrid scheme, the autonomous recovery is firstly transformed into the trajectory tracking problem, and the Dubins path planning method is adopted to build the three-dimensional(3D) motion path of AUV. Secondly, the virtual target guidance strategy is introduced to guide the AUV to track the desired path. Finally, a non-singular terminal sliding mode controller is designed to control the AUV. Due to the existence of model inaccuracy of AUV and external disturbances from the environment, a finite-time disturbance observer is adopted to estimate the disturbance and uncertainty in the system. Numerical simulation is conducted to verify its performance. The simulation results show that a 3D motion path can be planed and the AUV can track the motion path well.

An Active Fault-Tolerant Control for Robotic Manipulators Using Adaptive Non-Singular Fast Terminal Sliding Mode Control and Disturbance Observer

In this study, a fault-tolerant control (FTC) tactic using a sliding mode controller–observer method for uncertain and faulty robotic manipulators is proposed. First, a finite-time disturbance observer (DO) is proposed based on the sliding mode observer to approximate the lumped uncertainties and faults (LUaF). The observer offers high precision, quick convergence, low chattering, and finite-time convergence estimating information. Then, the estimated signal is employed to construct an adaptive non-singular fast terminal sliding mode control law, in which an adaptive law is employed to approximate the switching gain. This estimation helps the controller automatically adapt to the LUaF. Consequently, the combination of the proposed controller–observer approach delivers better qualities such as increased position tracking accuracy, reducing chattering effect, providing finite-time convergence, and robustness against the effect of the LUaF. The Lyapunov theory is employed to illustrate the robotic system’s stability and finite-time convergence. Finally, simulations using a 2-DOF serial robotic manipulator verify the efficacy of the proposed method.

Adaptive finite-time disturbance observer-based recursive fractional-order sliding mode control of redundantly actuated cable driving parallel robots under disturbances and input saturation

This paper proposed a novel finite-time disturbance observer-based recursive fractional-order sliding mode control (FTRFOSMC) algorithm under disturbances and input saturation for redundantly actuated cable driving parallel robots (RCDPRs). A recursive fractional-order sliding mode surface composed of the fractional-order non-singular fast terminal sliding mode function and an integral term is constructed, and the fast response convergence and high precision tracking performance can be obtained for the recursive characteristics of the proposed sliding mode surface; meanwhile, an auxiliary system is designed to overcome the adverse effects of the input saturation. Then, to compensate the model uncertainty and external disturbances, an adaptive finite-time disturbance observer is developed, and the estimation error can be stabilized in finite-time for unknown bound of the disturbance and its derivative. The stability of the proposed controller was investigated by the Lyapunov stability theory. Finally, numerical simulations with the software of the MATLAB/Simuink are conducted to verify the effectiveness of the proposed controller.

Finite-time disturbance observer based-control of flexible spacecraft

This paper aims to design an attitude controller for a flexible spacecraft under external disturbance and uncertainty. The spacecraft’s attitude is controlled by a super twisting controller based on a disturbance observer. This paper’s spacecraft system is non-minimum phase since mode-shapes are included in the output; thus, the following four methods are designed to compensate for the constraint: (1) The output redefinition method, where outputs are redefined as a combination of mode-shapes and quaternions. (2) The flexible spacecraft is controlled without measuring the mode-shapes, and only the quaternion parameters are selected as the output. (3) An advanced sliding surface is proposed, in which the mode-shapes are considered in the sliding surface. (4) The difference between flexible and rigid spacecraft dynamics is considered as disturbance, and its effect on the system is compensated. The finite-time stability of the closed-loop system is proved by leveraging the Lyapunov theory. The numerical simulation illustrates the closed-loop system’s effectiveness in terms of robustness compared to the existing controller and the four mentioned methods.

Learning-based online optimal sliding-mode control for space circumnavigation missions with input constraints and mismatched uncertainties

A learning-based online optimal sliding-mode control strategy is developed for space circumnavigation missions subject to input constraints, and the mismatched uncertainties caused by measurement uncertainties are also considered in this infinite-horizon optimal control problem. The logarithmic hyperbolic cosine function is used to design the optimal value function to overcome the weakness that the derivative of the adaptive weight of neural network (NN) changes too fast when the value of the sliding-mode function is too large, and another suitable nonquadratic function is used to incorporate input constraints into the optimal control framework. To approximate the Hamiton-Jacobi-Bellman equation corresponding to the novel optimal value function, an actor-critic (AC) architecture is introduced with NNs, and a finite-time disturbance observer (FTDO) is employed to estimate the mismatched uncertainties in the plant. The simulation results verify the effectiveness of the proposed approach.

Tracking control of uncertain surface vessels with global finite-time convergence

This paper investigates an innovative control technique for uncertain surface vessels working in enhanced sea states to guarantee global finite-time convergence. First, a new finite-time backstepping approach is investigated. However, the effects of the uncertainties and disturbances reduce the closed-loop performance and prevent the global finite-time convergence of the system. In order to estimate these effects, an innovative finite-time disturbance observer is taken into consideration. The combination between the finite-time backstepping approach and the finite-time disturbance estimation creates a control system providing finite-time convergence of the system. The proposed approach is then tested on a tracking control problem for a surface vessel. The simulation results unveil the innovation of the proposed approach compared with existing ones.

Protocol design for group output consensus of disturbed port-controlled Hamiltonian multi-agent systems

This paper considers the group output consensus problem for a class of disturbed port-controlled Hamiltonian multi-agent systems via a composite control method. The composite distributed control protocol is proposed by combining the damping injection and energy shaping method, the finite-time disturbance observer (FTDO) technique and distributed protocol, which makes the closed-loop Hamiltonian multi-agent systems asymptotically stable and the group outputs reach consensus. It is shown that many kinds of disturbances can be estimated accurately via the FTDO. The advantage is that this control scheme exhibits not only better robustness against disturbances, but also the nominal system recovery performance. Two illustrative examples reveal that the designed control protocol is effective.

Differential Aerodynamic Force-Based Formation Control of Nanosatellites Using Yaw Angle Deviation

This paper investigates a formation control technique for low-Earth-orbit nanosatellites based on the differential aerodynamic drag and lift. An innovative method of using only the yaw angle deviation, instead of the three-axis attitude rotation, is proposed to simultaneously control the in-plane and out-of-plane relative motions. This method can be used for the formation control of the Earth-pointing satellite. A control scheme consisting of four steps is designed considering complex input constraints. In this scheme, two control inputs are defined based on the predicted atmospheric density, and the explicit expressions of their time-varying feasible regions are analyzed. To obtain the yaw angle of each nanosatellite, a yaw angle solution algorithm based on the grid interpolation method is designed with online solving nonlinear optimization avoided. A dynamic surface control algorithm based on the hyperbolic tangent function and a linear model predictive control algorithm are, respectively, used to limit two control inputs within their feasible regions. In addition, a nonlinear finite-time disturbance observer is used to track the total system disturbance. Numerical simulations are carried out for along-track and circular formations, in which the uncertainties of aerodynamic forces, the attitude dynamics, and the unknown perturbation are taken into account.