Terminal Sliding Mode Control of Microgrid Inverter Systems

This paper proposes full-order terminal sliding-mode control strategies for wind energy conversion systems. Nonsingular terminal sliding-mode manifolds and related second-order sliding-mode control strategies are designed respectively for the d- and q-axis currents respectively. The control signals in the proposed sliding-mode controllers are continuous and have no chattering phenomenon. So the proposed controllers are suitable for practical applications.

Terminal sliding mode control for coordinated motion of a space rigid manipulator with external disturbance

In order to improve the anti-disturbance performance of permanent magnet synchronous motor (PMSM) servo system, a sliding-mode control strategy using a new reaching law (NRL) is proposed. The NRL incorporates power term and switching gain term of the system state variables into the conventional exponential reaching law (CERL), which can effectively suppress the sliding-mode chattering and increase the convergence rate of system state reaching sliding-mode surface. Based on this new reaching law, a sliding-mode speed controller (SMSC) of PMSM is designed. At the same time, to solve the chattering problem caused by the large sliding-mode switching gain, an anti-disturbance sliding-mode speed controller method with an extended sliding-mode disturbance observer (ESMDO), called SMSC+ESMDO method, is developed. The sliding-mode disturbance observer is designed to accurately estimate the motor speed and external load disturbances, and the disturbance estimator is used as a feed-forward to compensate the sliding-mode speed controller (SMSC) to improve the system robustness and reduce the system chattering. Simulation and experimental results show that the proposed compound sliding-mode control strategy can effectively improve the dynamic performance and robustness of the system compared with the PI controller.

This paper proposes high-order terminal sliding mode control strategies for wind energy conversion systems. Nonsingular terminal sliding mode manifolds and related second-order sliding mode control strategies are designed respectively for the speed controller and the current controllers of the induction generator in a wind energy conversion system. The second-order sliding mode technique is utilized to soften the non-smooth control signal, which can guarantee the actual control signal is continuous and smooth. The simulations are presented to validate the proposed method.

This paper introduces a variable structure to regulate speed of PMSM system by a global fast terminal sliding mode control (GFTSMC) technique optimizing speed tracking performance of permanent magnet synchronous motor (PMSM) servo system. Firstly, a global fast terminal sliding mode control strategy is introduced. Compared with common sliding mode control strategy, this strategy eliminates the chattering phenomenon in that it does not contain switching terms. Also, it can make the output speed reach the reference value in finite time, along with a shorter convergence time and a better tracking precision. Due to the complexity of control equations, S-function in MATLAB is adopted to design the GFTSMC. The effectiveness and robustness of the proposed scheme are verified by MATLAB simulations.

An adaptive fuzzy second-order terminal sliding mode control scheme is developed to solve the problem of rigid spacecraft attitude maneuver in which the external disturbances and uncertain inertia parameters as well as actuator faults are explicitly taken into account. The proposed controller incorporates a second-order terminal sliding mode to obtain finite time convergent performance as well as chattering elimination, meanwhile the fuzzy logical system is implemented to estimate the system uncertainties of the rigid spacecraft. Lyapunov stability analysis shows that the designed control algorithm guarantees the practical finite time stability of the attitude maneuver errors with great robustness to system uncertainties and actuator faults. Numerical simulations are also presented that not only highlights closed-loop performance benefits from the proposed control algorithm, but also illustrates its effectiveness in the presence of disturbances and uncertainties when compared with classic finite time sliding mode control schemes for spacecraft attitude maneuver control.

To improve the performance of the magnetorheological (MR) semi-active suspension system, a fractional-order sliding mode control (FOSMC) strategy is proposed to address the nonlinear problems caused by the external disturbances and changes in parameters of system. Firstly, The MR damper designed by the research team is applied to the vehicle’s MR semi-active suspension, and a one-fourth semi-active suspension dynamic model is established. Mechanical performance tests of the MR damper are conducted through tensile experiments, confirming its satisfactory mechanical characteristics and suitability for meeting the output damping force requirements of the vehicle’s semi-active suspension. To accurately convert the computed control force into the MR damper’s control current, an adaptive neuro-fuzzy inference system (ANFIS) inverse model of the MR damper is constructed. Comparative data analysis demonstrates the inverse model’s high accuracy and its ability to effectively meet the controller’s requirements. The proposed FOSMC strategy effectively reduces the chattering phenomenon associated with sliding mode control, leading to improved vibration-damping performance of the suspension. Subsequently, a simulation model and experimental platform are utilized to evaluate the performance of the proposed controller. Experimental results indicate that the FOSMC-controlled suspension outperforms the passive suspension, achieving significant reductions in body acceleration, suspension dynamic travel, and tire dynamic displacement by 27.4%, 7.3%, and 17.39%, respectively. Similarly, the semi-active suspension controlled by sliding mode control (SMC) also shows improvements compared to the passive suspension, with reductions in body acceleration, suspension dynamic travel, and tire dynamic displacement by 20.9%, 4.3%, and 5.2%, respectively. In summary, the FOSMC-controlled MR semi-active suspension exhibits superior damping performance compared to both the passive suspension and the SMC-controlled semi-active suspension, demonstrating the effectiveness of the proposed FOSMC controller.

This paper proposes a strategy of a new optimal sliding-mode control for flight control system with state constraints so that the system guarantees the optimal performance index. Besides, the strategy ensures strong robustness to the internal parametric uncertainty and the external disturbances. In order to have fast tran- sient response speed as well as good tracking accuracy, the integral of the time multiplied by the absolute dis- placement tracking error is introduced as the performance index. By analyzing the state constraints which are specifically the velocity tracking error constraint and the acceleration tracking error constraint, and the perfor- mance index, the parameters of sliding-mode surface and control law are obtained. Finally, the authors conduct the semi physical simulation on Qball-X4 quad-rotor helicopter, showing the effectiveness of the proposed strat- egy.

Improved sliding-mode control for a class of disturbed systems based on a disturbance observer

Multi-axis motion system is widely applied in commercial industrial machines such as precision CNC machine tools, Robot manipulator and laser cutting machines, etc. Contour accuracy plays a major role for the multi-axis servo motion system. The contour machining accuracy is related to the synthesis of single-axis position accuracy and multi-axis linkage accuracy. Only improving the single-axis tracking performance cannot effectively guarantee the machining accuracy of multi-axis system. The primary objective of this study was to design a contour control method to improve single-axis tracking accuracy and multi-axis contour accuracy. A control strategy that combines a sliding mode tracking controller, a disturbance observer and an adaptive fuzzy PID cross coupled controller is proposed. Sliding mode control is simple and has strong robustness to parameter changes and disturbance, which is especially suitable for control of such as non-linear multi-axis motion system. Besides, disturbance is inevitable in practical application, which degrades the motion accuracy. In order to eliminate the influence of external disturbance and uncertainty, disturbance observer is adopted to accurately estimate external disturbance and reduce the chattering phenomenon of sliding mode control, then improve the single-axis tracking accuracy. In order to further consider the coordination between different motion axes and improve the contour accuracy, the PID cross coupled control is used. Owing to conventional PID control cannot satisfy the multi-axis servo motion system with nonlinearity and uncertainty, an adaptive fuzzy method with on-line real-time PID parameters adjustment is proposed. The three-axis motion platform driven by PMLSM is used as the control object, to analysis the influence of disturbance observer on sliding mode control signal and analysis adaptive fuzzy PID cross coupled control performance respectively. The disturbance observer is used to observe the disturbance signal and estimate the disturbance well. The chattering of the sliding mode control signal is obviously improved. Next, compared with the conventional PID-CCC control, adaptive fuzzy PID- CCC control can significantly reduce the tracking error, the contour accuracy is also obviously improved. The disturbance observer can effectively eliminate the influence of external disturbance, reduce the chattering of sliding mode control, and ensure the single-axis accurate tracking. The self-adaptive fuzzy PID cross coupled controller can eliminate the influence of the dynamic characteristics mismatching and parameter difference of each axis, and improve contour accuracy. The simulation results clearly demonstrate the effectiveness of the proposed control method.

A manipulator often cannot converge rapidly within finite time and has low tracking accuracy owing to factors such as manipulator model errors and external disturbances. To address these problems, this paper proposes a time-varying non-singular fast terminal sliding mode control scheme based on an improved variable power–power reaching law. First, three radial basis function neural networks (RBFNNs) are employed to approximate the dynamic parameters of the manipulator model and thus realize model-free control. Second, to achieve faster finite-time convergence of the system state, a time-varying non-singular fast terminal sliding-mode (NFTSM) surface is designed according to the system state change. In addition, an improved variable power–power reaching law is adopted to avoid chatter and eliminate approximation errors. Finally, comparative simulation experiments are conducted using a 2-DOF manipulator as the research object. The results show that the proposed control scheme facilitates fast convergence, high-precision trajectory tracking, and effective suppression of system chatter under complex uncertainties, thereby confirming its utility and superiority.

This study proposes a robust controller in conjunction with the dynamic modeling of an existing three degrees of freedom planar parallel manipulator which can perform effectually in the presence of parameter uncertainties and external disturbances. The planar manipulator discussed here has three legs each with a prismatic-prismatic-revolute (3-PPR) joint configuration and located on the same plane connecting the moving platform which is in the form of an equilateral triangle. Each leg consists of an active prismatic joint, a passive prismatic joint and a passive rotary joint. The dynamic model has been obtained using the Euler-Lagrangian formulation method which is based on the kinetic and potential energies of the system. The proposed controller is based on a sliding mode control scheme with a nonlinear disturbance observer incorporated which aids in eliminating disturbances present in the system which is a result of both disturbances (internal and external disturbances) and parameter uncertainties which might arise due to un-modeled dynamics. Computer based numerical simulations are performed to demonstrate the effectiveness of the proposed control and results confirming the same in the presence of disturbances.

In this study, an adaptive fractional‐order terminal sliding mode controller is proposed for controlling robot manipulators with uncertainties and external disturbances. An adaptive tuning method is utilised to deal with uncertainties which upper bounds are unknown in practical cases. Fast convergence is achieved using non‐singular fast terminal sliding mode control. Also, fractional‐order controller is used to improve tracking performance of controller. After proposing a new stable fractional‐order non‐singular and non‐linear switching manifold, a sliding mode control law is designed. The stability of the closed‐loop system is proved by Lyapunov stability theorem. Simulation results demonstrate the effectiveness and high‐precision tracking performance of this controller in comparison with integer‐order terminal sliding mode controllers.

The paper propose a novel method for designing fault tolerant controller based on adaptive fast terminal sliding mode control to address the tracking control problem of spacecraft with unknown external disturbances and an uncertain inertia matrix. In this approach, a robust controller based on fast terminal sliding mode control scheme is designed in the absence of fault detection and diagnosis through adaptive approach which applied to estimate the fault minimum value of actuator fault. Through this approach, the closed-loop system globally asymptotically stability and fault tolerant control is achieved in the finite time while the disturbance is suppressed when actuaors fault occurred. Numerical simulations have demonstrated that the proposed approach could force the system to the equilibrium points in a fast convergence rate while improve the robustness and reliability with respect to common sliding mode method.

To solved the direct current (DC) link voltage fluctuation in Isolated shoot-through Z-source inverter (IST-ZSI). A switching controller based on sliding mode control and passivity-based control (PBC) for DC-link voltage of IST-ZSI is proposed. The IST-ZSI is assumed working in continuous conduction mode. At first, a DC link voltage sliding mode controller is designed, which uses inductor current error and DC link voltage error as state variables. The sliding mode control law is deduced, and the range of sliding coefficients is determined, which satisfy the existence and stable conditions. Secondly, the passivity based controller is designed by the dynamic equation of the IST-ZSI. In addition, a right switching function is selected to achieve the dynamic switching between the sliding mode controller and the passivity-based controller. This control method overcomes the chattering problem of sliding mode controller in steady state and accelerate the response speed of the system. And the system has strong robustness. Finally, the simulation results verify the effectiveness of the DC link voltage sliding mode controller.