Terminal Sliding Mode Control System Research Articles

Steady‐state analysis of discrete‐time nonsingular terminal sliding mode control systems based on Euler method

AbstractIn this article, the steady‐state behaviors of discrete‐time nonsingular terminal sliding mode (NTSM) control systems are investigated for the explicit and implicit Euler integration schemes. It is demonstrated that implicit Euler method can guarantee the global convergence of both system states and sliding variable for discrete‐time NTSM control systems, whereas explicit Euler approximation does not. For explicit discrete‐time NTSM, the range of quasi sliding mode band is deduced on the basis of the reachability condition of discrete SM, showing that discretized NTSM can achieve higher control accuracy than the discrete‐time linear sliding mode. By analyzing the distribution features of steady‐state points, the upper bound for steady states is obtained to estimate chattering amplitude, which establishes the influence relationship of sampling time, switching gain and movement characteristics on the bound of steady states. Simulations are presented to validate the theoretical results.

Second-order fuzzy sliding-mode control of photovoltaic power generation systems

In order to maximize the conversion efficiency of photovoltaic systems, it is usually essential to design a maximum power point tracking controller. In this paper, a new second-order fuzzy sliding-mode controller is designed for this purpose. Since the proposed scheme is based on the second-order sliding-mode control law, it can handle nonlinear dynamics of photovoltaic systems. Compared to previously introduced controllers, the proposed control law does not depend on model parameters and thus is robust to system uncertainties. The gain of the control signal is determined using a fuzzy gain tunning algorithm. Therefore, not only the robustness of the system will be improved, but also chattering amplitude will be suppressed. The proposed scheme does not require asymptotic observers, and thus its analysis and implementation are fairly simple. The performance of the proposed control system is verified through simulation and experiment. Compared to terminal sliding mode control system, the proposed system can increase the efficiency up to 1.5%.

Adaptive Fractional Order Terminal Sliding Mode Control of a Doubly Fed Induction Generator-Based Wind Energy System

The dynamic model of a doubly fed induction generator (DFIG)-based wind energy system is subjected to nonlinear dynamics, uncertainties, and external disturbances. In the presence of such nonlinear effects, a high-performance control system is required to guarantee the smooth and maximum power transfer from the wind energy system to the ac grids. This paper proposes a novel fractional order adaptive terminal sliding mode control system for both the rotor and grid side converters of the DFIG system. The stability of the closed loop is ensured using the fractional order Lyapunov theorem. Numerical results are presented to show the superiority of the proposed control method over the classical sliding mode control system and the proportional integral controllers.

Finite-Time Stabilization for Vehicle Active Suspension Systems With Hard Constraints

This paper presents the problem of finite-time stabilization for vehicle suspension systems with hard constraints based on terminal sliding-mode (TSM) control. As we know, one of the strong points of TSM control is its finite-time convergence to a given equilibrium of the system under consideration, which may be useful in specific applications. However, two main problems hindering the application of the TSM control are the singularity and chattering in TSM control systems. This paper proposes a novel second-order sliding-mode algorithm to soften the switching control law. The effect of the equivalent low-pass filter can be properly controlled in the algorithm based on requirements. Meantime, since the derivatives of term with fractional power do not appear in the control law, the control singularity is avoided. Thus, a chattering-free TSM control scheme for suspension systems is proposed, which allows both the chattering and singularity problems to be resolved. Finally, the effectiveness of the proposed approach is illustrated by both theoretical analysis and comparative experiment results.

Chattering free full-order sliding-mode control

In conventional sliding-mode control systems, the sliding-mode motion is of reduced order. Two main problems hindering the application of the sliding-mode control are the singularity in terminal sliding-mode control systems and the chattering in both the conventional linear sliding-mode and the terminal sliding-mode control systems. This paper proposes a chattering-free full-order terminal-sliding-mode control scheme. Since the derivatives of terms with fractional powers do not appear in the control law, the control singularities are avoided. A continuous control strategy is developed to achieve the chattering free sliding-mode control. During the ideal sliding-mode motion, the systems behave as a desirable full-order dynamics rather than a desirable reduced-order dynamics. A systematic design method of full-order sliding-mode control for nonlinear systems is presented, which allows both the chattering and singularity problems to be resolved. Simulations validate the proposed chattering free full-order sliding-mode control.

Discrete-Time Terminal Sliding Mode Control Systems Based on Euler's Discretization

In this technical note, the dynamical behaviors of discrete-time terminal sliding mode control systems based on Euler's discretization is investigated. Based on a recursive analysis, the boundedness for the steady states of the system is established. Theoretical analysis shows that the discrete-time terminal sliding mode control method can offer a higher output tracking precision than the discrete-time linear sliding mode control method. Simulations are given to verify the theoretical results.

Robust Nonsingular Terminal Sliding-Mode Control for Nonlinear Magnetic Bearing System

This study presents a robust nonsingular terminal sliding-mode control (RNTSMC) system to achieve finite time tracking control (FTTC) for the rotor position in the axial direction of a nonlinear thrust active magnetic bearing (TAMB) system. Compared with conventional sliding-mode control (SMC) with linear sliding surface, terminal sliding-mode control (TSMC) with nonlinear terminal sliding surface provides faster, finite time convergence, and higher control precision. In this study, first, the operating principles and dynamic model of the TAMB system using a linearized electromagnetic force model are introduced. Then, the TSMC system is designed for the TAMB to achieve FTTC. Moreover, in order to overcome the singularity problem of the TSMC, a nonsingular terminal sliding-mode control (NTSMC) system is proposed. Furthermore, since the control characteristics of the TAMB are highly nonlinear and time-varying, the RNTSMC system with a recurrent Hermite neural network (RHNN) uncertainty estimator is proposed to improve the control performance and increase the robustness of the TAMB control system. Using the proposed RNTSMC system, the bound of the lumped uncertainty of the TAMB is not required to be known in advance. Finally, some experimental results for the tracking of various reference trajectories demonstrate the validity of the proposed RNTSMC for practical TAMB applications.