This paper proposes an adaptive global terminal sliding mode control scheme for tracking control of uncertain nonlinear systems Using the proposed global sliding surface, the reaching period is omitted and the robust performance of the whole system is improved The discontinuous sign function is involved in the controller derivative and then, the control signal achieved after integration is continuous and attenuates the chattering problem Two adaptation laws are employed to cope with the uncertainties and disturbances whose upper bounds are not required to be known, where the proposed technique is more flexible in the real implementations This method guarantees robustness against uncertainties, disturbances and nonlinearities of the system Moreover, the proposed scheme removes the chattering phenomenon using the adaptive-tuning parameters and hyperbolic tangent function in the reaching control law Numerical simulations display the success and applicability of the proposed scheme in comparison with the results of the other method

Adaptive Global Terminal Sliding Mode Control Scheme with Improved Dynamic Surface for Uncertain Nonlinear Systems

For improving the convergence rate and time-varying disturbance rejection ability, an adaptive nonsingular terminal sliding mode controller based on disturbance compensation technique is proposed to control the position of magnetic levitation system in this article. First, the dynamical model of the magnetic levitation system is deduced, then a nonsingular terminal sliding mode control (NTSMC) is constructed. For reducing the chattering phenomenon, the time-varying disturbance estimation and compensation is cooperated into NTSMC controller using generalized proportional integral observer, the switching gain value could be chosen smaller, it could improve the system disturbance rejection, but the dynamic response is sacrificed to some extent. Thus, the adaptive NTSMC method is proposed for ensuring the dynamic and steady-state performance, the switching gain value could be tuned adaptively depending on the system states. When the system states are far away from the sliding mode surface, the gain value is large, else if the system states convergence to sliding mode surface, the value is small. Simulation and experimental results confirm the closed-loop performance both in dynamic response and disturbance attenuation, corresponding quantitative comparison could also show the advantages of the proposed control scheme.

Adaptive Terminal Sliding Mode Control for Magnetic Levitation Systems With Enhanced Disturbance Compensation

The electromagnet levitation system (ELS) of low-speed maglev train is taken as the research object. The nonlinear dynamics and control law of ELS are discussed. Specifically, by employing the Euler-Lagrange’s method, a nonlinear dynamic model is constructed for the single-ELS. Then, the linear control law is studied, which has a disadvantage of weak robustness. To improve the performance of the controller, a fuzzy sliding-mode control law is proposed. According to the dynamic nonlinear model, a novel sliding surface which can make the system reach the stable point within the finite time is presented. Moreover, the fuzzy inference method is utilized to slow down the speed of the states crossing the sliding surface. The simulation results demonstrate that the global robustness of external disturbance and parameter perturbation can be achieved through the proposed control law. And the chattering phenomenon can be reduced significantly. Finally, the experiments are also implemented to examine its practical dynamic performance of the proposed control law.

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Nonlinear dynamic modeling and fuzzy sliding-mode controlling of electromagnetic levitation system of low-speed maglev train

This study is concerned with the problem of H
 ∞
-integral sliding mode control (SMC) for one-sided Lipschitz (OSL) non-linear systems Unmatched norm-bounded uncertainties and disturbances are considered The design procedure gathers the high robustness qualities of the SMC and the H
 ∞
 measure performance Initially, the solvability condition for the integral sliding surface is established and new sufficient linear matrix inequality (LMI) condition is derived such that the sliding mode dynamics is robust exponentially stable and has a L
 2
 disturbance attenuation performance Then, an appropriate SMC law is synthesised to force the states of the system towards the sliding surface in finite time and to maintain a sliding motion on it thereafter At last, two simulation examples are provided to prove the feasibility of the proposed method

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-cta.2018.5510

Robust integral sliding mode- control of one-sided Lipschitz non-linear systems

The control performance of practical systems has inevitably suffered from various disturbances and uncertainties, including external environmental disturbances, unknown model uncertainties (possibly caused by unmodelled dynamics) and parameter perturbations. The development of disturbance observation and attenuation methods and technologies has received a great deal of attention for practical engineering systems. The new generations of control systems require increasingly higher control performance accuracy, and thus higher disturbance rejection abilities. In addition, the complexity of practical systems is much greater than those currently dealt with, for example, the extremely high dimensionality of these complex systems. This will result in the degraded disturbance rejection performance of the existing methods and technologies. The main objective of this Special Issue (SI) on ‘Disturbance Observers and Applications’ of the Transactions of the Institute of Measurement and Control is to present recent advances in disturbance observers and applications for practical control systems. The present SI will facilitate faster uptake of advanced disturbance observer technologies, as well as addressing new challenges arising from complex control systems, in order to give rise to new theories and methodologies. The interplay of disturbance observers and complex practical systems will largely advance the knowledge in both fields, resulting in much smarter methodologies and technologies to enhance the performance of the practical control systems. This SI consists of 16 papers selected from many highquality submissions through a strict peer-reviewed procedure. It covers some recent new progress in disturbance estimation and attenuations in both theoretical and application aspects. The contributions of the selected papers are categorised into four categories, which are briefly summarised as follows.

https://journals.sagepub.com/doi/pdf/10.1177/0142331216643049

Disturbance observers and applications

In this paper, a cascaded sliding mode control is designed for magnetic levitation systems usually comprised of an electrical loop and an electromechanical loop. A disturbance-observer-based sliding mode controller is designed for the electrical loop while a state-and-disturbance-observer-based sliding mode controller is designed for the electromechanical loop. The overall stability of the system is proved. The performance of the proposed scheme is compared with a conventional linear quadratic regulator combined with a proportional–integral controller by simulation as well as experimentation on a magnetic levitation setup in laboratory.

Chandrashekhar M Gutte

Papers

State-and-disturbance-observer-based sliding mode control of magnetic levitation systems: