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In this paper, an adaptive global fast terminal sliding mode control method using fuzzy-neural-network (FNN) is proposed for a single-phase photovoltaic (PV) grid-connected transformerless system that is mainly composed of a boost chopper and a dc-ac inverter. A maximum power point tracking is accomplished in the boost part in order to extract the maximum power from the PV array. A global fast terminal sliding mode control strategy is proposed for an H-bridge inverter so that the tracking error between a grid reference voltage and the output voltage of the inverter can converge to zero in finite time. FNN is used to estimate the uncertainties of the system in real time since uncertainties in the system are difficult to obtain. The network weights are updated according to the adaptive law in real time to adapt to the variations of system uncertainties, enhancing the robustness of the system. Finally, a PV grid-connected system model is built in Simulink to verify the effectiveness of the proposed adaptive global fast terminal sliding mode control method.

The active front steering (AFS) technique is one of the effective methods to handle the stability of a vehicle. In this paper, some AFS control schemes have been proposed. First, a two degree of freedom mathematical model for the vehicle dynamics has been introduced in order to calculate the desired yaw rate. On this basis, the actual sideslip angle is further identified and estimated by constructing a sliding-mode observer. Then, two kinds of baseline AFS controllers are proposed by using PID and terminal sliding mode techniques, such that the actual yaw rate will approach its reference value as closely as possible. To further improve the performance of the closed-loop AFS control system, taking the uncertainties and external disturbances into account, the composite control schemes are developed by combining the previous designed state-feedback controllers and feedforward compensation term generated by the disturbance observer. The effectiveness of the designed AFS control schemes is verified by using the Carsim Software. It has been verified that the performance under two composite controllers is better than both baseline controllers.

In this manuscript, the high-accuracy stator currents tracking issue is considered for a six-phase induction motor subject to external perturbations and uncertainties due to unmeasurable rotor currents and electrical parameter variations. To achieve the control goals, the common two-cascade controllers structure is required for this type of motor. The first controller in the outer loop consists of a proportional integral to regulate the speed. Then, the second is the proposed inner nonlinear stator currents controller based on a robust discrete-time terminal super-twisting algorithm supported by the time-delay estimation method. For the design procedure, the discrete-time stator currents dynamics are derived; for example, the vector of the matched perturbations and unmeasurable rotor currents are specified to simplify the estimation. A detailed stability analysis of the closed-loop error dynamics using Lyapunov theory is given. Finally, a real asymmetrical six-phase induction motor is used to implement in real-time the developed method and to illustrate its effectiveness and robustness. The results obtained reveal a satisfactory stator currents tracking in steady state and transient conditions and under variation in the magnetizing inductance. Moreover, a comparative study with an existing method in steady state for two different rotor speeds is presented to show the superiority of the proposed discrete-time technique.

In this paper, a finite-time control strategy based on back-stepping method combining with a terminal sliding mode control (TSMC) and a nonlinear disturbance observer (NDO) is proposed for the longitudinal dynamic model of hypersonic vehicle (HV). Firstly, the model of HV is transformed into two strict feedback subsystem: the mismatched subsystem of altitude and the matched subsystem of velocity. Then, the TSMC and back-stepping method is incorporated to cope with the unmatched issue in the HV altitude subsystem. In addition, a NDO based on a finite-time-convergent differentiator (FD) is proposed to estimate the lumped disturbances. The finite-time stability condition of the system is established via the Lyapunov theory. Finally, the robustness and effectiveness of the method are verified by simulations. [ABSTRACT FROM AUTHOR]

This article proposes a combination of linear and nonlinear sliding surfaces to design a new structure for terminal sliding mode control, capable of accepting a definite final time as an input data. The structures of both single-input-single-output and multi-input-multi-output systems are expressed. The controller operates in two modes: first, reaching the states to linear sliding surface, defining control parameters and rise time; second, switching to nonlinear sliding surface and defining a convergence time. Sum of rise time and convergence time, both of which as inputs, sets the final time. The control gains are adaptively tuned and parameter uncertainty in dynamics is considered in the design. The proposed method is implemented theoretically and experimentally on Scout robot in point-to-point motion and trajectory tracking. The results are compared to conventional terminal sliding mode control and finite-time state-dependent Riccati equation to assess the improvement. [ABSTRACT FROM AUTHOR]

This paper discusses the problem of adaptive sliding mode trajectory tracking control for wheeled mobile robots in the presence of external disturbances and inertia uncertainties. A new fast nonsingular terminal sliding mode surface without any constraint is proposed, which not only avoids singularity, but also retains the advantages of sliding mode control. In order to implement the trajectory tracking mission, the error dynamic system is divided into a second-order subsystem and a third-order one. First, an adaptive fast nonsingular terminal sliding mode control law of the angular velocity is constructed for stabilising the second-order subsystem in finite time. Then, another adaptive fast nonsingular terminal sliding mode control law of the linear velocity is designed to guarantee the stability of the third-order subsystem. Finally, a simulation example is provided to demonstrate the validity of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Summary: Note that the amplitude of chattering existing in the sliding mode control method is proportional to the magnitude of the control gain. Therefore, the key issue to diminish the chattering is to decrease the value of sliding mode controller's gain to an acceptable minimal level defined by the so‐called reaching condition for the sliding mode's existence. For this reason, the nonsingular terminal sliding mode (NTSM) control method and the adaptive technique have been considered in this paper to develop a novel adaptive NTSM control method, which can be used to search the minimal value of the control gain automatically in the presence of the external disturbances. Meanwhile, the average value of a high‐frequency switching signal in the adaptive law can be provided by Arie Levant's differentiator rather than a low‐pass filter. The rigorous mathematical proof verifies that the system states can converge to the origin within a finite time under the proposed adaptive NTSM controller. Both the academic example and the practical application to an active front steering system are illustrated to show that the presented adaptive NTSM controller has better control performance than the conventional sliding mode controller. [ABSTRACT FROM AUTHOR]

This study proposes an adaptive sliding mode disturbance rejection control with prescribed performance for robotic manipulators. A transformation with respect to tracking error using certain performance functions is used to ensure the transient and steady-state performances of the trajectory tracking control for robotic manipulators. Using the transformed error, a nonsingular terminal sliding mode surface is proposed. A continuous terminal sliding mode control (SMC) is presented to stabilize the system. To compensate for the uncertainty and external disturbance, a novel sliding mode disturbance observer is proposed. Considering the unknown boundary of the derivative of a lumped disturbance, an adaptive law based on the idea of equivalent control is designed. Combining the adaptive law, continuous nonsingular terminal SMC, and sliding mode disturbance observer, the adaptive sliding mode disturbance rejection control with prescribed performance is developed. Simulations are carried out to demonstrate the effectiveness of the proposed approach. • A nonsingular terminal sliding mode surface is presented. • A novel sliding mode disturbance rejection control is proposed. • An adaptive law based on the ideal of equivalent control is introduced. • The practical finite time convergence and prescribed performance are achieved. [ABSTRACT FROM AUTHOR]

A tracking controller design problem for the discrete-time uncertain systems is investigated in this paper. A discrete-time terminal sliding-mode tracking controller is designed to achieve high-performance tracking with alleviated chattering phenomenon. A novel reaching-law is proposed which reduces the bandwidth of the quasi-sliding-mode domain and suppresses the chattering. Furthermore, the reaching process and the bound of the tracking error are analyzed in detail. Finally, comparative experimental results are presented to illustrate the effectiveness and advantages of the proposed strategy. [ABSTRACT FROM AUTHOR]

In this paper, a novel adaptive control approach for Unmanned Aerial Manipulators (UAMs) is proposed. The UAMs are a new configuration of the Unmanned Arial Vehicles (UAVs) which are characterized by several inhered nonlinearities, uncertainties and coupling. The studied UAM is a Quadrotor endowed with two degrees of freedom robotic arm. The main objectives of our contribution are to achieve both a tracking error convergence by avoiding any singularity problem and also the chattering amplitude attenuation in the presence of perturbations. Therefore, the proposed Adaptive Nonsingular Terminal Super-Twisting controller (ANTSTW) consists of the hybridization of a Nonsingular Terminal Sliding Mode Control and an Adaptive Super Twisting. The adaptive law, which adjust the Super-Twisting's parameters, is obtained by using stability Lyapunov theorem. Simulation experiments in trajectory tracking mode were realized and compared with Nonsingular Terminal Super-twisting control to prove the superiority and the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, a fast form of nonsingular, terminal, decoupled, sliding-mode control, which utilizes timevarying sliding surfaces, is proposed for a class of fourth-order, single-input, multioutput, nonlinear systems. The novel control law features a fast term, in the manner of fast terminal sliding-mode control, which markedly improves the finite-time sliding-mode convergence speed near zero. Numerical simulation results, which are illustrated with a cartpole inverted pendulum system and a ball-beam system, demonstrate that the proposed control law achieves, in general, favorable transient response and lower steady-state errors compared to state-of-the-art decoupled terminal sliding-mode control methods. [ABSTRACT FROM AUTHOR]

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Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract This paper proposes an output feedback continuous terminal sliding mode guidance law (CTSMGL) for three-dimensional missile-target interception with consideration of second-order autopilot dynamics. The proposed output feedback CTSMGL not only guarantees the rates of the line-of-sight angles converge to zero in finite time but also ensures the continuity of control action. Besides, only the relative range and velocity information of guidance system has been utilized in its design process. Simulations of a practical interception process under three types of maneuvering targets are carried out and the simulation results illustrate the effectiveness of the proposed guidance method. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhengzhou University (Natural Science Edition) is the property of Journal of Zhengzhou University (Natural Science Edition) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper describes a novel finite-time attitude tracking control approach for flexible spacecraft. This is achieved by integrating sliding-mode control and the active real-time fault-tolerant reconfiguration method. In this approach, the attitude error dynamics and the kinematics of the flexible spacecraft are first established. Then, a nonsingular terminal sliding-mode surface is designed, based on finite-time control theory. Applying the Chebyshev neural network, the uncertain dynamics induced by external disturbances and uncertain inertia parameters are approximated and estimated. The nominal control law and the compensation control law to obtain the active reconfiguration fault-tolerant controller are finally developed in normal and fault conditions, respectively. The closed-loop tracking system is proved to be uniformly ultimately bounded stable after a finite time. Numerical simulations are presented for a flexible spacecraft to illustrate the efficiency of the proposed controller. [ABSTRACT FROM AUTHOR]

Abstract The major hurdles to control the force created by piezoelectric actuators (PEAs) are originated from its strong nonlinear behaviors which include hysteresis, creep, and vibration dynamics. To achieve an accurate, fast and robust force tracking performance without using complicated modeling and parameter identification of PEAs, this paper presents a practical direct force control scheme. The proposed controller is based on two core approaches: 1) fast finite-time integral terminal sliding mode (FFI-TSM) which allows fast convergence and high accuracy to the closed-loop system without control chattering; and 2) an inverse-model-free compensation, named force-based time-delayed estimation (FBTDE) which offers significant robustness with minimum use of plant dynamics information. The finite-time stability of the overall closed-loop system is proven through the Lyapunov's method. The proposed force tracking controller is implemented on the PEA system driving a variable physical damping actuator mechanism. The overall accuracy, convergence speed, and robustness of the proposed controller are validated under various experimental scenarios. Comparative experimental results are particularly presented to verify the effectiveness of the FFI-TSM term and the FBTDE term. [ABSTRACT FROM AUTHOR]

Two nonlinear state observers are proposed to reconstruct the system states for a class of uncertain nonlinear systems. Both state observers are designed based on continuous higher order sliding mode and terminal sliding mode concepts. The proposed observers are chattering-free and constructed without any detailed model knowledge of the system. Desirable features of the proposed observers include that they are immune to noise and can be designed separately from a controller. Lyapunov stability theory is employed to prove the finite-time convergent and uniformly ultimately bounded observation. Simulation results are provided to demonstrate the effectiveness and improved performance of the developed observers. [ABSTRACT FROM AUTHOR]

Background: Piezoelectric actuators are widely used in many micro/nano-manipulation applications, but their positioning accuracy are badly affected by their inherent nonlinear hysteresis and creep. To solve this problem, this paper presents a new robust motion-control method for piezoelectric actuators with fast nonsingular terminal sliding mode based on time delay estimation. Method: The proposed controller needs no detailed information about the hysteresis and other nonlinearities of the system, leading to a simple and model-free characteristic due to the time delay estimation and ensures fast convergence and high tracking accuracy thanks to the nonsingular terminal sliding-mode surface and fast terminal sliding mode-type reaching law. A robust exact differentiator is adopted to estimate the velocity and accelerationinformation online, and it overcomes the limitation of only available position measurements. The finite-time convergence and stability of the closed-loop system are proved by using a Lyapunov function. Results: Experimental results show that the proposed control strategy has faster convergence and higher tracking precision compared with a traditional time delay control. Conclusion: The proposed control strategy can be widely used as an effective control method for high-precision motion control of piezoelectric actuators. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a new fixed-time control algorithm to enable autonomous landing of a helicopter onto the ship's deck in the presence of parametric uncertainties and external disturbances. A nonsingular terminal sliding control is implemented as an integral part of the fixed-time control scheme, that guarantees the convergence of system errors to zero in a fixed settling time, however, without the consideration of disturbances. Subsequently, a fixed-time disturbance observer is incorporated into the control structure to efficiently estimate the lumped disturbances including modeling inaccuracies and external perturbations, while reducing the undesired chattering in the control inputs effectively as well. By establishing a relative motion model between the helicopter and the ship, the shipboard landing problem is converted from a general trajectory tracking problem to a more favorable stabilization problem. Based on the fixed-time control scheme in the relative motion model, a relative position controller (RPC) and a relative attitude-altitude controller (RAC) are formulated to guide the helicopter in a dual-phase landing sequence. The RPC will first be implemented to direct the helicopter from its initial position to a hover position above the ship. The next phase involves the application of RAC to guide the helicopter to descend steadily on the ship. Numerical comparative simulations are also carried out to validate the remarkable performance of the proposed control approach. [ABSTRACT FROM AUTHOR]

This paper investigates the continuous finite‐time control problem of high‐order uncertain nonlinear systems with mismatched disturbances through the terminal sliding mode control method. By constructing a novel dynamic terminal sliding manifold based on the disturbance estimations of high‐order sliding mode observers, a continuous finite‐time terminal sliding mode control method is developed to counteract mismatched disturbances. To avoid discontinuous control action, the switching terms of a dynamic terminal sliding manifold are designed to appear only in the derivative term of the control variable. To validate its effectiveness, the proposed control method is applied to a DC‐DC buck converter system. The experimental results show the proposed method exhibits better control performance than a chattering free controller, such as mismatched disturbances rejection and smaller steady‐state fluctuations. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to solve the position tracking control problem for the permanent magnet linear motor by using the discrete-time fast terminal sliding mode control (SMC) method. Specifically, based on Euler's discretization technique, the approximate discrete-time model is first obtained and analyzed. Then, by introducing a new type of discrete-time fast terminal sliding surface, an improved discrete-time fast SMC method is developed and an equivalent-control-based fast terminal SMC law is subsequently designed. Rigorous analysis is provided to demonstrate that the fast terminal SMC law can offer a higher accuracy than the traditional linear SMC law. Numerical simulations and experimental results are finally performed to demonstrate the effectiveness of the proposed approach and show the advantages of the present discrete-time fast terminal SMC approach over some existing approaches, such as discrete-time linear sliding mode control approach and the PID control method. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a predefined-time terminal sliding mode approach for attitude tracking control of unmanned aerial vehicle (UAV). In order to obtain the high convergence speed and steady-state performance controller, the modified non-singular terminal sliding mode control (TSMC) we adopted can switch sliding mode surfaces under different conditions. The system stability is achieved within a predefined time, which can be set by modifying the explicit parameters in advance. Due to the existence of model uncertainties and unknown external disturbances, an adaptive neural network-based approach is applied to compensate the error between the actual and nominal model without requiring any prior knowledge of the disturbances. Several comparative studies are carried out between the proposed approach and other predefined-time techniques in previous work, and simulation results and experimental results are presented to validate the correctness of analysis and superiority of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Tracking guidance commands for a time-varying aerospace launch vehicle during the atmospheric flight is considered in this paper. Hence, the dynamic terminal sliding mode control law is constructed for this purpose and dynamic sliding mode control is utilized. The terminal sliding manifold causes the dynamic sliding mode to converge asymptotically to zero in finite-time. The actuator and rate gyro dynamics are included in the model of launch vehicle. Dynamic sliding mode control accommodates unmatched disturbances, while the terminal sliding mode control is used to accelerate the system to reach the dynamic sliding manifold. Finally, the effectiveness of the proposed control is demonstrated in the presence of unmatched disturbances and is compared with the dynamic sliding mode.