Fractional-order Sliding Mode Control Scheme Research Articles

Adaptive sliding mode tracking control of underwater vehicle-manipulator systems considering dynamic disturbance

This paper proposes an adaptive sliding mode tracking control method with a nonlinear disturbance observer (NDO-ASMTC) to solve the trajectory tracking problem of the underwater vehicle-manipulator system (UVMS) in the presence of large dynamic uncertainties and severe external disturbances. The proposed NDO-ASMTC method employs an adaptive control law, an improved fractional-order sliding mode, and a nonlinear disturbance observer to achieve excellent tracking performance of the UVMS. To obtain a fast response speed in the sliding mode phase and eliminate static error in the reaching phase, a modified fractional-order sliding mode control scheme is proposed. An adaptive auto-tuning law of switching gains is presented to overcome the problem that the fixed switching gain may lead to obvious tracking performance degradation under lumped uncertainty. In addition, a nonlinear disturbance observer is implemented to maintain the robustness and stability of the control scheme under severe disturbances. Moreover, the proposed adaptive control scheme has been proved to be stable using the Lyapunov theorem. Simulations and experiments show that the proposed control scheme can meet the design requirements of the UVMS in terms of tracking accuracy, system stability, and interference attenuation under the application of external disturbances.

Adaptive Control Design for Euler–Lagrange Systems Using Fixed-Time Fractional Integral Sliding Mode Scheme

This paper presents an adaptive fixed-time fractional integral control for externally disturbed Euler–Lagrange systems. In the first step of the control design, the approach of fractional-order fixed-time integral nonsingular terminal sliding mode control (FoIFxTSM) is introduced. This scheme combines the benefits of fractional calculus with integral sliding mode control, resulting in fast convergence, smooth nonsingular control inputs, and fixed-time stability. By integrating an adaptive scheme, the proposed method is used to control the dynamical system in the presence of uncertainty and external perturbations. The findings of the fixed-time stability using Lyapunov analyses are provided for the closed-loop system. The simulation results are compared with the adaptive fractional-order sliding mode control scheme, and they show the better tracking and convergence performance of the proposed method.

Adaptive Fractional-Order Fast-Terminal-Type Sliding Mode Control for Underwater Vehicle-Manipulator Systems

Abstract This article proposes an adaptive fractional-order fast-terminal-type sliding mode control method to solve the trajectory tracking problem of the underwater vehicle-manipulator system in the presence of large dynamic uncertainties and strong external disturbances. For improving the control continuity and accuracy of the conventional sliding mode control method, a modified fractional-order sliding mode control scheme with a novel fractional-order sliding manifold and a fast-terminal-type reaching law is proposed. In addition, an auto-tuning law of switching gains is presented and combined with the fractional-order sliding mode control scheme to overcome the problem that the fixed switching gain may lead to obvious tracking performance degradation under complicated lumped disturbances. Finally, the superiorities of the proposed adaptive fractional-order fast-terminal-type sliding mode control method are verified through a series of comparative simulations of a 6-degrees-of-freedom (DOF) UVMS carrying a 6DOF manipulator.

Disturbance observer-based fractional-order sliding mode control for free-floating space manipulator with disturbance

This paper proposes a fractional-order sliding mode control scheme based on disturbance observer for tracking control of free-floating space manipulators (FFSM), regarding system uncertainties and disturbances. To mitigate the effect of disturbance, a fast fractional-order disturbance observer (FFODOB) is proposed, which can estimate the disturbances in finite time. It relaxes the assumption of first-order differentiable of the disturbances, which is common in many existing disturbance observers, to continuous but not necessarily differentiable, making it more suitable for practical applications. Besides, a new fractional-order nonsingular terminal sliding mode (FONTSM) controller is designed, in which, a fractional-order integral term is introduced into the conventional nonsingular terminal sliding mode surface. The presented FONTSM improves the transient response and tracking precision of FFSM. Stability of the closed-loop system and finite-time convergence are proved theoretically. Simulations are performed for different situations, and the results demonstrate the effectiveness and superiorities of the proposed methods over the existing methods.

Nonlinear Predictive Optimization for Deploying Space Tethered Satellite via Discrete-Time Fractional-Order Sliding Mode

This article develops a discrete-time fractional-order sliding mode control scheme to deploy space tethered satellite, with the nonlinear predictive optimization of underactuated dynamics. Firstly, by the discrete-time Euler–Lagrangian mechanics, the discrete-time dynamical equations are derived for the tether deployment, and some preliminaries of discrete-time fractional-order calculus are prepared. Secondly, a model predictive control (MPC)-based hybrid sliding manifold is designed based on the discrete-time fractional-order sliding mode and nonsingular terminal sliding mode. These two sliding modes correspond to the actuated and underactuated states of tethered system, whose nonlinear coupling is explicitly regulated by MPC optimization. Then, an MPC-based discrete-time fractional-order sliding mode control is raised to drive system states onto the hybrid sliding manifold, by solving the online optimization problem of the contractive MPC scheme. Furthermore, a compensation analysis of input saturation is presented to deal with the adverse impact of saturated tension, and realize a more stable early deployment. Finally, numerical simulations and comparisons of tether deployment are performed, to verify the effectiveness and superiority of the proposed scheme.

RBF Neural Network Fractional-Order Sliding Mode Control with an Application to Direct a Three Matrix Converter under an Unbalanced Grid

This paper presents a fractional-order sliding mode control scheme based on an RBF neural network (RBFFOSMC) for a direct three matrix converter (DTMC) operating under unbalanced grid voltages. The RBF neural network (RBF NN) is designed to approximate a nonlinear fractional-order sliding mode controller. The proposed method aims to achieve constant active power whilst maintaining a near unity input power factor. First, an opportune reference current is accurately generated according to the reference power and the RBFFOSMC is designed in a dq reference frame to achieve a perfect tracking of the input current reference. An almost constant active power, free of low-frequency ripples, is then supplied from the grid after compensating for the output voltage. Simulation and experimental studies prove the feasibility and effectiveness of the proposed control method.

Adaptive Fractional-Order Non-Singular Fast Terminal Sliding Mode Control Based on Fixed Time Disturbance Observer for Manipulators

In this study, with the help of a disturbance observer, an adaptive fractional-order sliding mode control scheme is designed to achieve trajectory tracking control of indeterminate manipulators. Firstly, the fractional-order non-singular fast terminal sliding mode (FO-NFTSM) surface is presented to increase the convergence velocity of the controller. Secondly, the adaptive reaching law is designed on the strength of the super-twisting algorithm to ensure the control performance of the approaching stage. Meanwhile, aiming at the compound disturbance existing in the manipulator system, an adaptive fixed-time sliding mode disturbance observer (AFSMDO) is introduced to settle the problem, which can estimate the lumped disturbance in real-time. Moreover, compensate for the system and raise the precision of the controller. The Lyapunov method is applied to certify the stability of the control system. Simulation experiments verify the superior property of the controller designed in this article.

Closed Loop Control of Photo Voltaic Emulator Using Fractional Calculus

Threatening environmental effects have forced the community to utilize green and clean alternative options for the generation of electric power. As a matter of fact, solar energy is a critical source of energy; so the demand for creative research is its peak. However, performing real time experiments on solar PV systems is limited by cost, manufacturing, weather constraints and requirement of large space. Thus an equivalent solar energy photo voltaic (PV) system is required for experimental verification and analysis based on precise simulations. In this research work a PV emulator system based on a buck converter is realized. The main objective of PV Emulator is to replicate the characteristic curves (I-V, P-V) of the real solar panel. In order to compensate the variations in both the load and the parameters of power stage, a robust control system is required. A fractional order sliding mode control scheme (FOSMC) has been designed and investigated in this research work. Results have proved the superior performance of the FOSMC as compared to other classical sliding mode control method. The FOSMC controller and PV emulator are implemented using rapid prototyping technique.

Double-Hidden-Layer Recurrent Neural Network Fractional-Order Sliding Mode Control of Shunt Active Power Filter

In this paper, a fractional-order sliding mode control scheme based on a double-hidden-layer recurrent neural network is proposed for a single-phase shunt active power filter. Considering the shortcomings of traditional neural networks that the approximation accuracy is not high and weight and center vector of neural networks are unchangeable, a new double-hidden-layer recurrent neural network structure which contains two hidden layers to make the network have more powerful fitting ability, is designed to approximate the unknown nonlinearities. An original output feedback neural network with two hidden layers is designed to estimate the uncertainties regardless of unknown system characteristics and external disturbances. A fractional-order term is added to the sliding mode controller to have more adjustable space and better optimization space. Experimental results verified the validity of the designed controller and proved that it can complete the current compensation well with acceptable current tracking error, demonstrating the outstanding compensation performance and strong robustness

Practical Position Tracking Control of a Robotic Manipulator Based on Fractional Order Sliding Mode Controller

In this study, the practical position tracking control of a robotic manipulator has been performed using the proposed fractional-order sliding mode control scheme (FO-SMC). The designed control technique is composed by fractional calculus and sliding mode control (SMC) to guarantee the fast convergence of the joint positions to their desired values. The main idea behind the design of the FO-SMC control is that, the sliding mode control composed with fractional calculus contributes to reach a robust control performance of a nonlinear system in presence of uncertainties, disturbances and un-modelled dynamics without a complete dynamic model of the system. To validate and demonstrate the performance of FO-SMC method, an industrial robot manipulator with external load has been used in the real time experimental studies. The experimental outcomes demonstrate that the proposed fractional-order sliding mode control strategy has a better trajectory tracking performance in presence of the external payload for tracking tasks compared with the classical SMC.DOI: http://dx.doi.org/10.5755/j01.eie.24.5.21838

Robust position-based impedance control of lightweight single-link flexible robots interacting with the unknown environment via a fractional-order sliding mode controller

SUMMARYThis paper presents a fractional-order sliding mode control scheme equipped with a disturbance observer for robust impedance control of a single-link flexible robot arm when it comes into contact with an unknown environment. In this research, the impedance control problem is studied for both unconstrained and constrained maneuvers. The proposed control strategy is robust with respect to the changes of the environment parameters (such as stiffness and damping coefficient), the unknown Coulomb friction disturbances, payload, and viscous friction variations. The proposed control scheme is also valid for both unconstrained and constrained motions. Our novel approach automatically switches from the free to the constrained motion mode using a simple algorithm of contact detection. In this regard, an impedance control scheme is proposed with the inner loop position control. This means that in the free motion, the applied force to the environment is zero and the reference trajectory for the inner loop position control is the desired trajectory. However, in the constrained motion the reference trajectory for the inner loop is determined by the desired impedance dynamics. Stability of the closed loop control system is proved by Lyapunov theory. Several numerical simulations are carried out to indicate the capability and the effectiveness of the proposed control scheme.

A novel fractional sliding mode control configuration for synchronizing disturbed fractional-order chaotic systems

In this paper, a new design of fractional-order sliding mode control scheme is proposed for the synchronization of a class of nonlinear fractional-order systems with chaotic behaviour. The considered design approach provides a set of fractional-order laws that guarantee asymptotic stability of fractional-order chaotic systems in the sense of the Lyapunov stability theorem. Two illustrative simulation examples on the fractional-order Genesio–Tesi chaotic systems and the fractional-order modified Jerk systems are provided. These examples show the effectiveness and robustness of this control solution.