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.
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- "Moreover, its stiffness and damping can be changed through rotor displacement and velocity feedback control. In recent years, many intelligent control techniques, such as fuzzy control, adaptive PID control, neural networks control , adaptive fuzzy control, and other control methods, have been developed and applied to the position control for AMB system      . Although fuzzy control has been successfully applied in several industrial automations, it is not an easy task to obtain an optimal set of fuzzy membership functions and rules in FLC. "
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ABSTRACT: Studies on active magnetic bearing (AMB) systems are increasing in popularity and practical applications. Magnetic bearings cause less noise, friction, and vibration than the conventional mechanical bearings; however, the control of AMB systems requires further investigation. The magnetic force has a highly nonlinear relation to the control current and the air gap. This paper proposes an intelligent control method for positioning an AMB system that uses a neural fuzzy controller (NFC). The mathematical model of an AMB system comprises identification followed by collection of information from this system. A fuzzy logic controller (FLC), the parameters of which are adjusted using a radial basis function neural network (RBFNN), is applied to the unbalanced vibration in an AMB system. The AMB system exhibited a satisfactory control performance, with low overshoot, and produced improved transient and steady-state responses under various operating conditions. The NFC has been verified on a prototype AMB system. The proposed controller can be feasibly applied to AMB systems exposed to various external disturbances; demonstrating the effectiveness of the NFC with self-learning and self-improving capacities is proven.
Available from: Xian-Ming Zhang
- "Answering this question will significantly enrich the control theory of the offshore platform, which is the second motivation of this paper. Since sliding mode control is an efficient control method to enhance the system robustness against parameter perturbations and unmodeled dynamic uncertainties , , it has a wide range of applications in various areas, such as micromanipulator , magnetic bearing systems , offshore container crane , and offshore platforms . In this paper, we develop a novel sliding mode control scheme for an offshore steel jacket platform subjected to nonlinear self-excited wave force and parameter perturbations. "
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ABSTRACT: This paper is concerned with active control for an offshore steel jacket platform subjected to wave-induced force and parameter perturbations. An uncertain dynamic model for the offshore platform is first established, where uncertainties not only on the natural frequency and the damping ratio of both the offshore platform and the active tuned mass damper (TMD) but also on the damping and stiffness of the TMD are considered. Then, by intentionally introducing a proper time delay into the control channel, a novel sliding mode control scheme is proposed. This scheme uses information about mixed current and delayed states. It is shown through simulation results that this scheme is more effective in both improving the control performance and reducing control force of the offshore platform than some existing ones, such as delay-free sliding mode control, nonlinear control, dynamic output feedback control, and delayed dynamic output feedback control. Furthermore, it is shown that the introduced time delay in this scheme can take values in different ranges while the corresponding control performance of the offshore platform is almost at the same level.
Available from: Jing-Jing Xiong
- "A continuous finite-time control scheme for rigid robotic manipulators using a new form of terminal sliding modes was proposed in . For the sake of achieving finite-time tracking control for the rotor position in the axial direction of a nonlinear thrust active magnetic bearing system, the robust non-singular TSMC was given in . However, the conventional TSMC methods are not the best in the convergence time, the primary reason is that the convergence speed of the nonlinear sliding mode is slower than the linear sliding mode when the state variables are close to the equilibrium points. "
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ABSTRACT: A synthesis control method is proposed to perform the position and attitude tracking control of the dynamical model of a small quadrotor unmanned aerial vehicle (UAV), where the dynamical model is underactuated, highly-coupled and nonlinear. Firstly, the dynamical model is divided into a fully actuated subsystem and an underactuated subsystem. Secondly, a controller of the fully actuated subsystem is designed through a novel robust terminal sliding mode control (TSMC) algorithm, which is utilized to guarantee all state variables converge to their desired values in short time, the convergence time is so small that the state variables are acted as time invariants in the underactuated subsystem, and, a controller of the underactuated subsystem is designed via sliding mode control (SMC), in addition, the stabilities of the subsystems are demonstrated by Lyapunov theory, respectively. Lastly, in order to demonstrate the robustness of the proposed control method, the aerodynamic forces and moments and air drag taken as external disturbances are taken into account, the obtained simulation results show that the synthesis control method has good performance in terms of position and attitude tracking when faced with external disturbances.
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