Search

In order to improve the tracking accuracy of the linear maglev synchronous motor maglev system with non-linear, strongly coupled, and other uncertainty problems, a fixed-time fractional order terminal sliding mode control (FFTSMC) strategy based on adaptive fixed-time extended state observer (AFxESO) is proposed. Firstly, a fast AFxESO is constructed and an adaptive law is designed to dynamically adjust the gain to reduce the estimation error and measurement noise, which enables the observer to accurately estimate the perturbation of the unknown boundary in a fixed-time. Secondly, a new FFTSM controller is designed by applying the theory of fractional order calculus, which can speed up the system convergence and suppress the chattering problem in SMC. Then, using the Lyapunov stability theory, it is demonstrated that the proposed AFxESO-FFTSM control scheme can guarantee the global fixed-time convergence of the system to equilibrium and the convergence time is dependent on the selection of the controller parameters, which effectively overcomes the drawbacks of finite-time control. Finally, the feasibility and superiority of the proposed strategy are verified on the linear maglev synchronous motor system experiment platform. [ABSTRACT FROM AUTHOR]

This paper investigates the finite‐time synchronization issue of Takagi‐Sugeno (T‐S) fuzzy stochastic complex networks (TSFSCN) with disturbances and time‐varying delays using the preassigned‐time sliding mode control (SMC) strategy. A novel fuzzy SMC law is designed by introducing a time‐varying function, ensuring that the error system reaches the sliding mode surface (SMS) within any preassigned time and converges to zero along the SMS. The arrival time and sliding time are independent of design parameters and initial values, enhancing the stability and controllability of the system. Additionally, the adoption of a continuous function to replace the sign function reduces the chattering phenomenon in the system. Based on Lyapunov theory and finite‐time SMC strategy, a sufficient condition is derived for the system to achieve arbitrary preassigned‐time synchronization. Finally, the effectiveness of the proposed control method is verified through two examples. [ABSTRACT FROM AUTHOR]

This study utilized a sliding mode control (SMC) technique combined with modified exponential reaching law to address the control of a nonlinear system. The introduced adaptive reaching law enables the system trajectories to converge rapidly toward the origin, surpassing the convergence speed achieved by the existing reaching laws. By employing the suggested reaching law, the SMC exhibits remarkable performance while effectively mitigating chattering. Furthermore, the proposed reaching law enables the system trajectories to converge rapidly toward the origin, surpassing the convergence speed achieved by the existing reaching laws. This article includes simulation results and a comparison with other predominantly existing approaches to highlight the superior performance of the proposed reaching law. [ABSTRACT FROM AUTHOR]

Controlling variable wind speed turbine (VWT) system based on a doubly-fed induction generator (DFIG) is a challenging task. It requires a control law that is both adaptable and robust enough to handle the complex dynamics of the closed control loop system. Sliding mode control (SMC) is a robust control technology that has shown good performance when employed as a passive fault-tolerant control for wind energy systems. To improve the closed control loop of VWT based on DFIG with the aim of improving energy efficiency, even in presence of nonlinearities and a certain range of bounded parametric uncertainties, whether electrically or mechanically, an adaptive passive fault tolerant control (AP-FTC) based on a self-tuning fractional integral sliding mode control law (ST-FISMC) developed from a novel hyperbolic fractional surface is proposed in this paper. ST-FISMC introduces a nonlinear hyperbolic function into the sliding manifold for self-tuning adaptation of control law, while fractional integral of the control law smooths discontinuous sign function to reduce chattering. Additionally, this work introduces an adaptive observer, developed and proved based on a chosen Lyapunov function. This observer is designed to estimate variations in electrical parameters and stator flux, ensuring sensorless decoupling in indirect field-oriented control (SI-FOC) of DFIG. Lyapunov theory is also used to prove stability of states vectors in closed control loop with presence of bounded parameters uncertainties or external disturbances. Simulation results show that the proposed approach offers better performance in capturing optimal wind energy, as well as the ability to regulate active/reactive power and high resilience in presence of occurring parameter uncertainties or external disturbances. [ABSTRACT FROM AUTHOR]

The well known back-propagation algorithm has revolutionized machine learning and artificial intelligence, particularly in neural network applications. Although gradient descent-based algorithms are utilized in control applications, they are not as prevalent as in neural network applications. This discrepancy can be attributed to the successful development of various adaptation laws which ensure system stability while meeting the required design criteria. Many of these laws can be found in model reference adaptive control (MRAC) and adaptive sliding mode control (ASMC). This paper investigates the applicability of the Brandt-Lin (B-L) learning algorithm, mathematically equivalent to the back-propagation algorithm, in adaptive control applications. We find that combining the B-L learning algorithm with SMC yields a robust controller suitable for model reference adaptive sliding mode control (MRA-SMC). The controller is applicable to linear and a class of nonlinear dynamic systems and is suitable for efficient implementation. We derive the stability criteria for this controller and conduct simulations to study the adaptation's impact on chattering. Our work exemplifies one approach to adopt the back-propagation algorithm in control applications. [ABSTRACT FROM AUTHOR]

Controlling variable wind speed turbine (VWT) system based on a doubly-fed induction generator (DFIG) is a challenging task. It requires a control law that is both adaptable and robust enough to handle the complex dynamics of the closed control loop system. Sliding mode control (SMC) is a robust control technology that has shown good performance when employed as a passive fault-tolerant control for wind energy systems. To improve the closed control loop of VWT based on DFIG with the aim of improving energy efficiency, even in presence of nonlinearities and a certain range of bounded parametric uncertainties, whether electrically or mechanically, an adaptive passive fault tolerant control (AP-FTC) based on a self-tuning fractional integral sliding mode control law (ST-FISMC) developed from a novel hyperbolic fractional surface is proposed in this paper. ST-FISMC introduces a nonlinear hyperbolic function into the sliding manifold for self-tuning adaptation of control law, while fractional integral of the control law smooths discontinuous sign function to reduce chattering. Additionally, this work introduces an adaptive observer, developed and proved based on a chosen Lyapunov function. This observer is designed to estimate variations in electrical parameters and stator flux, ensuring sensorless decoupling in indirect field- oriented control (SI-FOC) of DFIG. Lyapunov theory is also used to prove stability of states vectors in closed control loop with presence of bounded parameters uncertainties or external disturbances. Simulation results show that the proposed approach offers better performance in capturing optimal wind energy, as well as the ability to regulate active/reactive power and high resilience in presence of occurring parameter uncertainties or external disturbances.

Oxygen stoichiometry (OS) and stack temperature (ST) significantly affect the output performance and durability of proton exchange membrane fuel cells. This paper investigates the prescribed performance tracking control strategy of OS and ST under external disturbances, modeling errors, actuators faults and limited communication resources. The total disturbances are compensated by a variable-bandwidth extended state observer to simplify the control design and enhance the system robustness. To tolerate excessive disturbances and relax the strict requirement on the initial conditions, a new event-triggered adaptive sliding mode controller that integrates modified dynamic performance constraints and nonsingular error transformation is developed to ensure the user-designed transient and steady-state performance constraints, while saving the communication costs and avoiding the chattering and jump in control signals. The numerical validation results under combined working scenarios indicate that the proposed controller always ensures the preset error constraints and possesses superior performance in tracking the optimal OS value 2 and the optimal ST value 353.15K than other three representative controllers, with the integral absolute errors of 0.732 for OS tracking and 12.94 for ST tracking; besides, it achieves satisfactory robustness to uncertain model parameters and relatively large initial tracking errors. [Display omitted] • A robust event-triggered prescribed performance controller for PEM fuel cell systems. • Oxygen stoichiometry (OS) and stack temperature (ST) are simultaneously controlled. • Integral absolute errors when tracking OS and ST are 0.732 and 12.94 respectively. • A better compromise between control performance and communication cost. • The chattering and jump phenomena in control signals are suppressed. [ABSTRACT FROM AUTHOR]

A higher-order sliding approach to control a bioreactor model is proposed by non-commensurate fractional equations. The model outputs by the help of a controller reached the desired values and track them. According to existing conditions and chattering reduction, a high-order sliding mode has been chosen to design the controller. The purpose of the paper is to choose proper sliding surfaces. Here, for a better conclusion, a comparison has been made between the high-order sliding mode and the standard sliding mode. High-order sliding mode controllers have been taken in accordance with the structure of integer order system. Thus, in order for the system to apply more precise calculations, it should somehow turn to integer order. The sliding surfaces have been selected so appropriately that we can benefit from the structure of integer order controllers for fractional order system. The sliding surface in both controllers has also been the same so as to provide conditions for comparison. Finally, simulation results indicate that the high-order sliding mode controller has a great impact on chattering reduction.

This paper integrates extended state observer into sliding mode controller for better transient and steady-state performance and robustness against nonlinearity, uncertainty, and time-varying disturbance. The design process of the proposed controller is composed of two main stages. Firstly, all the nonlinearity, uncertainty, and time-varying disturbance of the system are considered as the total disturbance, which is estimated by a designed high-order extended state observer (HESO). Secondly, by integrating the sliding mode control into the HESO, the composite controller is formed. Benefits from HESO's disturbance estimation and online compensation, the problem of chattering is substantially alleviated. Thanks to the sliding mode term, the closed-loop system will converge to the reference even under severe disturbances. The numerical and experimental results for a calibration-free robotic hand-eye coordination system indicate the effectiveness and robustness of the proposed approach. [ABSTRACT FROM AUTHOR]

Copyright of Laser Technology is the property of Gai Kan Bian Wei Hui 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 aims to develop a chattering-reduction sliding mode control (SMC) approach for affine systems with input matrix uncertainty. Input matrix uncertainty poses adverse effects on systems, such as aggravating the chattering effect, and even causing instability for systems. To solve this problem, a two-step controller design method is proposed in this paper. In the first step, a general sliding mode controller is designed for the system without input matrix uncertainty. To suppress the effect of input matrix uncertainty, in the second step, a control term is specially developed to compensate for input matrix uncertainty. This term is obtained by solving a nonlinear equation, in which the directional characteristics of the control vector in the first step are integrated into the control term. By adding up the control terms obtained from the above two steps, a refined controller is obtained whose control gain is significantly reduced, especially facing with large input matrix uncertainty. In addition, the efficacy of the designed controller was verified in the simulation of a nonlinear plant. Upon drawing a comparison of the proposed method with a state-of-the-art SMC algorithm, it is learnt that the proposed controller is able to provide the closed-loop system with a more desired performance in which the amplitude of chattering is greatly reduced.

The quadcopter unmanned aerial vehicle (UAV) system is considered a good platform for control scheme design as it is highly nonlinear with coupled dynamics and an under-actuated system. Considering these challenges, this manuscript aimed to propose a control algorithm to control the quadcopter system in the presence of uncertainty and disturbance influences. The integral adaptive sliding mode control scheme has been proposed to control the system. The proposed control scheme is composed of the outer loop controller to control the position of the quadcopter, while the inner loop controls the attitude of the quadcopter. The proposed control law has three major terms, firstly the equivalent control which is developed based on the Lyapunov approach to handle most of the uncertainty and disturbance, secondly the adaptive switching gain, which is achieving fast adaptation against uncertainty, finally the switching function which has been approximated by a tangent hyperbolic function to reduce the unwanted chattering phenomena. The proposed control scheme and its performance have been investigated via a MATLAB/Simulink. The results prove that the implemented control scheme is robust even in the presence of uncertainties and disturbance and the quadcopter tracks the predefined trajectories with limited chattering influence.

In this paper, the problem of the preassigned-time synchronization is studied for a class of delayed fuzzy cellular neural networks with discontinuous activations via preassigned-time control. Above all, with the help of the existing classical fixed-time stability theory and via variable substitutions, a new fixed-time stability result is established, and the derived estimation of settling times are tighter than the existing ones. Subsequently, as applications of the new fixed-time stability results, a novel preassigned-time stability theorem is derived, and some novel and useful sufficient criteria are obtained to guarantee that the addressed neural networks achieve preassigned-time synchronization. The preassigned synchronization time is not only independent of the initial value, system and controller parameters, but also can be preassigned in advance based on the actual needs. Additionally, to suppress or eliminate the chattering phenomenon, a saturation function is designed to replace the sign function in the controller, and its effectiveness has been verified by numerical simulation. Especially, one of the power exponents of the two differently designed preassigned-time controllers can change smartly instead of being a fixed constant. Lastly, two numerical examples with simulations are given to present the effectiveness of the obtained results. [ABSTRACT FROM AUTHOR]

Fixed-time stability (FXTS) and fixed-time control (FXTC) of dynamic systems are reconsidered in this article based on special functions from the view of improving the estimate accuracy of settling time (ST) and reducing the chattering caused by the sign function. First, by means of the idea of contradiction and variable transformations, some generic FXTS criteria are established and some upper bounds of ST are directly calculated and expressed by several special functions. It is further proved that these estimates are the most accurate compared with the existing results. Besides, to suppress the chattering caused by the sign function, some saturation functions are constructed to replace the sign function and the FXTS of the new system obtained by replacing is ensured by rigorous theoretical analysis. As applications, the problem of stabilization for chaotic systems in fixed or preassigned time is explored. Especially, an innovative saturation controller is developed to realize preassigned-time stabilization, where the convergence time is prescribed in advance according to actual requirement and the control gains are finite, the existing control methods with time-varying infinite gains are essentially improved. Lastly, three numerical examples are provided to verify the improved estimates of ST and the chattering reduction. [ABSTRACT FROM AUTHOR]

Sliding mode control, an algorithm known for its stability and robustness, has been widely used in designing robot controllers. Such controllers inevitably exhibit chattering; numerous methods have been proposed to deal with this problem in the past decade. However, in most scenarios, ensuring that the specified form and the parameters selected are optimal for the system is challenging. In this work, the reinforcement-learning method is adopted to explore the optimal nonlinear function to reduce chattering. Based on a conventional reference model for sliding mode control, the network output directly participates in the controller calculation without any restrictions. Additionally, a two-step verification method is proposed, including simulation under input delay and external disturbance and actual experiments using a quadrotor. Two types of classic chattering reduction methods are implemented on the same basic controller for comparison. The experiment results indicate that the proposed method could effectively reduce chattering and exhibit better tracking performance.

This article presents a simple and systematic approach to synthesize a robust adaptive fuzzy fractional-order nonsingular terminal sliding mode controller (AFFO-NTSMC) to improve the output voltage tracking control performance of the dc–dc buck converters. The hybrid control method of fractional-order (FO) calculus and NTSMC are combined to create a FO-NTSMC, in which a new FO nonsingular terminal sliding mode surface is established. The idea behind this strategy is the increased flexibility achieved by FO calculation, improving robustness to disturbances and parameters variations provided by the traditional sliding mode controllers as well as finite time convergence properties of the output voltage error to the equilibrium point during the output load changes, simultaneously. In addition, a fuzzy logic system with online adaptive learning algorithm is designed to provide smooth chattering in switching control signal. The stability of the closed-loop system is carefully demonstrated by Lyapunov's theorem. Experimental measurements from a laboratory prototype are presented to demonstrate the effectiveness of the proposed AFFO-NSTSMC algorithm. [ABSTRACT FROM AUTHOR]

The chattering problem is caused by the switching function of sliding mode controller, which makes the accuracy of autonomous driving limited. To solve this problem, a steering sliding mode controller with improved nonlinear reaching law is proposed. The exponential function is used in the new reaching law to eliminate chattering problem, and the initial value of switching function is employed to avoid output saturation in the case of large initial errors. In the new reaching law, the large slope of sign function coefficient ensures the anti-disturbance ability of the controller after the system converges. A disturbance observer is constructed for real-time observation of the disturbance signals, which makes the controller get rid of the dependence on the prior knowledge of the disturbance. This paper introduces the tuning principle of controller parameters in detail and constructs the simulations and experiments of autonomous driving system. The experiments demonstrate that the proposed controller restrains the path-tracking mean error by 38% and restrains the standard error by 18%, the accuracy and efficiency of autonomous driving system are improved. Furthermore, the proposed reaching law can be used in other systems besides autonomous harvesting robots. [ABSTRACT FROM AUTHOR]

First order Sliding Mode Control (SMC1) is used to control robotic manipulators deployed in industrial applications. However, the tracking performance of SMC1 is affected by modelling uncertainties, disturbance, and noisy measurement signals. In addition, SMC1 introduces an undesirable chattering effect that causes vibrations and reduces the manipulator positioning accuracy. This work investigates deployment of a Quasi-Continuous second order Sliding Mode Control (QCSMC) and its stability, over a nonlinear multilink Revolute-Revolute (RR) manipulator, to enhance the manipulator tracking performance, and reduce the chattering effect under the presence of modelling uncertainties, disturbance, and noisy state measurement. This investigation work introduces the manipulator’s dynamics modelling, forward and inverse kinematic solutions. The study then shows the desired joint space trajectory solution, whereby modelling uncertainties are considered. The work presents an online uncertainty quantification analysis to investigate the controller performance and stability with parameter change. SMC1 and QCSMC are then deployed to follow extracted trajectories under the effect of model-parameter-change, noisy measurement, and disturbance signals. Simulation results show that performance of QCSMC, overcomes the performance of SMC1, under the considered simulation conditions. Simulation results were further endorsed through experimentation methods by an NXT-based RR manipulator prototype. Simulation results demonstrate that applying QCSMC have reduced the associated joint-space trajectory root mean square errors (RMSE) when compared to SMC1 associated RMSE results. The enhancement reached an average of (84% to 97%) with infused model change and (64% to 79%) enhancement with infused disturbance. However, QCSMC shows a 2% RMSE value enhancement for the case of infused measurement noise when compared to SMC1. Experimental results demonstrate that the associated RMSE have also reduced by applying QCSMC when compared to SMC1. The experimental scenario nature includes a combined effect of modelling uncertainties, disturbances and measurement noise all applied together. Experimental scenario 1 shows that applying QCSMC have reduced the tracking RMSE for the first revolute joint angular position by 10%, and for the second joint angular position by 5% when compared to SMC 1 associated tracking RMSE values. Experimental scenario 2 shows a similar trend with 3% RMSE tracking enhancement for the second joint angular position when QCSMC is applied. Simulation and Experimental results agree, QCSMC introduces a better performance than SMC1, implying an enhanced performance, with less tracking errors, reduced chattering effect and higher robustness with reduced vibrations. In addition, the provided results signify robustness of both controllers against uncertainties and noise with better performance for QCSMC over SMC1. [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicles (UAVs) have been widely applied over the past decades, especially in the military field. Due to the unpredictability of the flight environment and failures, higher requirements are placed on the design of the control system of the fixed-wing UAV. In this study, a sliding mode disturbance observer-based (SMDO) adaptive dynamic inversion fault-tolerant controller was designed, which includes an outer-loop sliding mode observer-based disturbance suppression dynamic inversion controller and an inner-loop real-time aerodynamic identification-based adaptive fault-tolerant dynamic inversion controller. The sliding mode disturbance observer in the outer-loop controller was designed based on the second-order super-twisting algorithm to alleviate chattering. The aerodynamic identification in the inner-loop controller adopts the recursive least squares algorithm to update the aerodynamic model of the UAV online, thereby realizing the fault-tolerant control for the control surface damage. The effectiveness of the proposed SMDO enhanced adaptive fault-tolerant control method was validated by mathematical simulation.

This research proposes a nonlinear adaptive controller based on a hierarchical sliding mode control (HSMC) framework to stabilize the operation of a ridable ballbot based on the full nonlinear dynamics (FND). The FND of ballbots is a multiple‐input‐multiple‐output underactuated system with a non‐invertible input matrix. By applying a novel approach to transform the FND into two subsystems, the invertibility of the input matrix of the transformed subsystems can be guaranteed. Thus, an HSMC scheme can be applied to control the ridable ballbot system based on stabilizing the transformed subsystems. In addition, to improve the robustness of HSMC, a new adaptive law is proposed to deal with the effects of exogenous disturbances and parameter variations on the modeled dynamics. Chattering and actuator saturation phenomena are also reduced or avoided with the proposed controller. Comparative simulations are conducted to demonstrate the merit features of the proposed approach and the robustness of the developed control algorithm. [ABSTRACT FROM AUTHOR]

The super-twisting algorithm (STA, a class of second-order sliding mode control (SOSMC)) is widely used in permanent magnet linear synchronous motor (PMLSM) systems for its least amount of information and simplest calculations among the SOSMC algorithms. Due to the discretization and sign function of the STA, the chattering problem may be induced. In this paper, we propose an STA method with a defined boundary layer (called δSTA) to further reduce chattering in high-precision positioning system. With the δSTA method, when the sliding variable crosses the zero point, the speed is adjusted via two different saturation functions, instead of discontinuous sign functions of the STA. The proposed control law was proven to be stable, ensuring the establishment of a second-order sliding mode. Both the simulation and experimental results showed that the proposed control scheme, with a defined boundary layer width, can improve the steady-state positioning accuracy and significantly reduce system chattering. [ABSTRACT FROM AUTHOR]

This paper is mainly dedicated to the challenging issue of fixed-time attitude control for a flexible spacecraft in the presence of actuator faults, external disturbances and coupling effect of flexible modes. The attitude controller is developed by employing a fixed-time nonsingular terminal sliding mode under which the convergence time is bounded and independent of the initial states. This robust attitude controller is able to provide superior properties such as fast fixed-time attitude manoeuvring with high pointing accuracy, singularity avoidance and chattering free. More specifically, a new reaching law is employed to provide convergence rate improvement as well as chattering alleviating simultaneously. The actuator fault problem is also considered and the attitude control is achieved even when the actuators experience severe faults. The proposed controller ensures that the closed-loop attitude system is stable in the sense of fixed-time stability concept. Furthermore, since the upper bound of external disturbances and flexible vibrations acting on the spacecraft is not available, an adaptation mechanism is presented. Numerical simulations demonstrate that the proposed controller is able to successfully accomplish attitude control with high attitude pointing accuracy and stability in spite of the actuator faults, flexible structures vibrations and external disturbances. [ABSTRACT FROM AUTHOR]

This paper presents a high precision compound control scheme based on non-singular terminal sliding mode and extended state observer (ESO) for an aerial inertially stabilized platform (ISP) to suppress the effects of multi-source disturbances on the control performance of the ISP. Firstly, a non-singular terminal sliding mode controller is proposed to achieve high disturbance rejection ability, by which the multi-source disturbances are integrally suppressed as an aggregate disturbance. And then, to restrain the chattering effect of the sliding mode control, a disturbance compensation scheme based on the extended state observer is proposed. By the ESO, the disturbances are observed and compensated in real time and hence the chattering effect is significantly alleviated. Meanwhile, a parameter configuration method is proposed to simplify the ESO design. To verify the method, simulations and experiments are conducted. The results show that the proposed compound control scheme has excellent ability in both disturbance rejection and chattering reduction, by which the stabilization precision of the ISP is improved significantly. [ABSTRACT FROM AUTHOR]

The electro-optical tracking system (ETS) on moving platforms is affected by the vibration of the moving carrier, the wind resistance torque in motion, the uncertainty of mechanisms and the nonlinear friction between frames and other disturbances, which may lead to the instability of the electro-optical tracking platform. Sliding mode control (SMC) has strong robustness to system disturbances and unknown dynamic external signals, which can enhance the disturbance suppression ability of ETSs. However, the strong robustness of SMC requires greater switching gain, which causes serious chattering. At the same time, the tracking accuracy of SMC has room for further improvement. Therefore, in order to solve the chattering problem of SMC and improve the tracking accuracy of SMC, an SMC controller based on internal model control (IMC) is proposed. Compared with traditional SMC, the proposed method can be used to suppress the strongest disturbance with the smallest switching gain, effectively solving the chattering problem of the SMC, while improving the tracking accuracy of the system. In addition, to reduce the adverse influence of sensor noise on the control effect, lifting wavelet threshold de-noising is introduced into the control structure to further improve the tracking accuracy of the system. The simulation and experimental results verify the superiority of the proposed control method.

This study deals with the problem of controlling rotor speed and stator currents of an asymmetrical six‐phase induction machine with uncertain dynamics, disturbances, and unmeasurable rotor currents and proposes a robust non‐linear variable structure controller. First of all, an outer control loop based on a proportional–integral regulator is performed to control the rotor speed and to construct the desired stator current references. Then, the inner loop is performed based on the proposed method that combines the time delay estimation method and discrete sliding mode control based on exponential reaching law. This structure allows an accurate and simple estimation of uncertainties and rotor currents, a high‐tracking precision, a convergence of the stator currents to their known desired references in finite‐time and chattering reduction. The design procedure is detailed step by step and the stability analysis and the convergence time are established for the current closed‐loop system. Experimental work was carried out on an asymmetrical six‐phase induction motor drive to show the effectiveness and performance of the proposed robust non‐linear discrete method. The results obtained highlighted the good tracking performance of the stator currents. [ABSTRACT FROM AUTHOR]

The design of a robust controller is a challenging task due to nonlinear behaviour of the glider and surround environment. This paper presents design and simulation of nonlinear robust integral super-twisting sliding mode control for controlling the longitudinal plane of an autonomous underwater glider (AUG). The controller is designed for trajectory tracking problem in existence of external disturbance and parameter variations for pitching angle and net buoyancy of the longitudinal plane of an AUG. The algorithm is designed based on integral sliding mode control and super-twisting sliding mode control. The performance of the proposed controller is compared to original integral sliding mode and original super-twisting algorithm. The simulation results have shown that the proposed controller demonstrates satisfactory performance and also reduces the chattering effect and control effort. [ABSTRACT FROM AUTHOR]

This paper presents a review of sliding mode control for autonomous underwater vehicles (AUVs). The AUVs are used under water operating in the presence of uncertainties (due to hydrodynamics coefficients) and external disturbances (due to water currents, waves, etc.). Sliding mode controller is one of the nonlinear robust controllers which is robust towards uncertainties, parameter variations and external disturbances. The evolution of sliding mode control in motion control studies of autonomous underwater vehicles is summarized throughout for the last three decades. The performance of the controller is examined based on the chattering reduction, accuracy (steady state error reduction), and robustness against perturbation. The review on sliding mode control for AUVs provides insights for readers to design new techniques and algorithms, to enhance the existing family of sliding mode control strategies into a new one or to merge and re-supervise the control techniques with other control strategies, in which, the aim is to obtain good controller design for AUVs in terms of great performance, stability and robustness. [ABSTRACT FROM AUTHOR]

This article seeks to achieve high tracking performance of the hybrid automobile electro-coating conveying mechanism with disturbances and uncertainties. An integral sliding mode control scheme is first presented to eliminate the reaching phase in sliding mode control. Then, an adaptive integral sliding mode controller is designed without knowing the disturbance information. Finally, a composite strategy, referred to as nonlinear disturbance observer (NDO)-based adaptive integral sliding model control, is put forward to further reduce the switching gain. By compensating the lumped disturbances via a NDO, the switching gain is only required to be higher than upper bound of the disturbance estimation error which is much smaller than actual disturbance. The results of both numerical simulations and experiments show that the proposed approach has good control performance especially in reducing the switching gain and alleviating the chattering problem. [ABSTRACT FROM AUTHOR]

In this study, a quasi-continuous high-order sliding mode control approach is presented for the longitudinal model of a generic hypersonic flight vehicle with parametric uncertainties and actuator faults. The quasi-continuous high-order sliding mode controller is designed to track the responses of the normal system to guarantee the velocity and altitude track the reference trajectories rapidly. An improved measure by increasing the relative degree of the quasi-continuous high-order sliding mode is introduced to eliminate the effects on outputs caused by chattering and parametric uncertainties. In view of actuator coupling, an equivalent canonical model is formulated through feedback linearization to accelerate the faults estimation for the actuator faults system. A neural network observer is then utilized to online estimate the unknown faults. This observer can be applied to highly nonlinear system without any prior knowledge of system dynamics as it uses a nonlinear-in-parameters neural network. Meanwhile, the stability and convergence of the faults system is proved theoretically. Simulation results are presented to testify the effectiveness and robustness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

In robot control, the sliding mode control is known for its robustness against external disturbances and system uncertainties. However, it has the disadvantage of control chattering, which can damage the actuator and degrade system performance. With a new stability proof, this paper presents an alternative simple linear feedback control that can cope with large system uncertainties and suppress large external disturbances, doing so as effectively as sliding mode control does. The advantage of using linear control is that the control law is simple and control chattering can be avoided. Moreover, a noise-free control scheme is proposed as an improvement of the feedback control; the modified design preserves the advantages of linear control and generates a chattering-free control signal even in a noisy environment.

In this paper, we present a fractional sliding mode controller based on a robust observer for fractional systems with bounded disturbances. This controller is introduced to achieve closed-loop Mittag-Leffler stability for uncertain fractional systems; meanwhile, the robust observer is designed such that a stability is obtained via quadratic Lyapunov functions and the tuning is achieved with linear matrix inequality approach. The performance and stability of the proposed controller are analysed and demonstrated through a generalised -differentiator. Finally, to illustrate the effectiveness of the proposed approach a comparative analysis against the fractional Super-Twisting is carried out. [ABSTRACT FROM AUTHOR]

The ocean bottom flying node (OBFN) is a novel autonomous underwater vehicle (AUV) system which could explore the oil and gas resources in deep water. This paper investigates the distributed finite-time chattering reduction containment control problem for multiple OBFNs under directed communication topology. The model uncertainties and external disturbances are considered. By defining the containment error variables and selecting high-order sliding variable properly, a distributed finite-time containment control strategy is developed. The discontinuous sign function is contained in the derivative of the control protocol so as to eliminate the chattering phenomenon. An adaptive law is designed to make efficiency estimation and compensation for the upper bounds of model uncertainties and external disturbances. Combined with the graph theory and matrix theory, the Lyapunov method is utilized to demonstrate that the follower OBFNs could enter the convex hull formed by the leader OBFNs in finite time. Numerical simulation is provided to show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract The DC–DC power converter plays an important role in solar systems to provide the stable DC bus voltage, but which is easily subject to various uncertainties and disturbances in practical operation. In this paper, an uncertainty and disturbance estimator (UDE) based sliding mode control approach is applied to improve the performance of power converters. The UDE is designed for the estimation of both the matched and mismatched uncertainties. To address the mismatched uncertainties, an adaptive sliding mode function is constructed with the compensation of the estimated uncertainties, which renders a chattering-free robust control law. Simulation and experimental results illustrate that the proposed control scheme achieves good dynamic performance, strong robustness and chattering reduction in the presence of uncertainties and disturbances Highlights • A novel sliding mode controller is applied to address mismatched uncertainties. • Uncertainty and disturbance estimator is designed without the knowledge of bounds. • The estimator-based robust controller is developed to eliminate the chattering phenomena. • Simulation and experimental validation on power converters are carried out. [ABSTRACT FROM AUTHOR]

This paper investigates the control issue of uncertain systems in presenting of time-varying delay and stochastic disturbance. The state information is real-timely measured by the sensor and directly sent to an event-trigger, then only necessary data is transmitted by the event-trigger to the controller while the rest redundant information is simply discarded. Since the controller receives a discontinuous-time data sequence, an observer is designed to restructure a substitutional continuous-time state and an observer-state-dependent sliding mode control law is proposed. By the proposed method, not only the mean square exponential stability of closed-loop system can be guaranteed almost surely but also the data transmission amount can be reduced. In addition, the chattering behaviour can be alleviated, meanwhile, the match conditions of uncertainty and disturbance are not required. More significantly, the Zeno phenomena of the event-trigger can be conveniently excluded and the minimal event-triggering interval is also given. A numerical example is provided to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the application of a novel switching integral-exponential-adaptation-law-based adaptive sliding mode control design for a wide class of nonlinear systems with unknown polynomial bounds on the uncertainty norm. A robust finite time convergence, i.e. finite stability, is obtained with low chatter on control actions and a fast-transient performance for adaptive sliding mode control handling the multi-input multi-output nonlinear systems with uncertainties of amplitudes bounded within unknown polynomials in the state vector norm. The exponential term of the proposed adaptation law targets the reduction of the chatter levels of the sliding mode by significantly reducing the gain overestimation while simultaneously suppressing the overshoot by speeding up the system response to the uncertainties. It also prevents the instability issues which encounters the classic integral-gain-law-based adaptive sliding mode control when underestimating its initial gain or gain rate parameter. A simple example illustrates the motivation and feasibility of the proposed adaptive sliding mode control. The applications on a nonlinear mass–spring system and on a two degree of freedom electromechanical rotative plant demonstrate the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

This paper presents a sliding mode control scheme for chaotic systems. Finite time stability of the system states is realized by implementing the proposed controller, which is designed on the basis of a nonlinear sliding surface and a new sliding mode reaching law. The new reaching law contributes good control performance in terms of system reaching time and input chattering reduction. Principles for controller parameter selection are given in detail. Simulation results of two controlled chaotic systems are provided to demonstrate effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

As higher requirements are proposed for the load regulation and efficiency enhancement, the control performance of boiler-turbine systems has become much more important. In this paper, a novel robust control approach is proposed to improve the coordinated control performance for subcritical boiler-turbine units. To capture the key features of the boiler-turbine system, a nonlinear control-oriented model is established and validated with the history operation data of a 300 MW unit. To achieve system linearization and decoupling, an adaptive feedback linearization strategy is proposed, which could asymptotically eliminate the linearization error caused by the model uncertainties. Based on the linearized boiler-turbine system, a second-order sliding mode controller is designed with the super-twisting algorithm. Moreover, the closed-loop system is proved robustly stable with respect to uncertainties and disturbances. Simulation results are presented to illustrate the effectiveness of the proposed control scheme, which achieves excellent tracking performance, strong robustness and chattering reduction. [ABSTRACT FROM AUTHOR]

This paper presents a prescribed-time output stabilization method for mismatched uncertain systems using state-feedback control and extended disturbance compensation. The settling-time interval is divided into a disturbance-estimation interval plus an output-stabilization interval, where a prescribed-time extended disturbance observer with finite time-varying gains (PTFG-EDO) and a modified time–space deformation approach (TSDA) control are applied in these intervals, respectively. Due to the prescribed-time convergence of the PTFG-EDO and the modified TSDA control, the settling time of the closed-loop system can be predetermined irrespective of the initial conditions, design parameters, and admissible disturbances. The chattering problem of the original TSDA control is greatly alleviated, and the disturbances, especially the mismatched disturbance which cannot be handled in the original TSDA control, are significantly suppressed. The effectiveness of the proposed PTFG-EDO-based control is demonstrated via numerical simulations. [ABSTRACT FROM AUTHOR]

To improve the accuracy of torque control for vector control of interior permanent-magnet synchronous machine (IPMSM), this study proposes a torque-sensorless control method based on cascaded sliding mode observer (SMO). First, the active flux model is discussed, which converts the model of IPMSM into the equivalent model of surface-mounted permanent-magnet synchronous machine. Second, to reduce chattering caused by system parameters variations and external disturbances, the cascaded observer is designed, which is composed of a variable gain adaptive SMO and an active flux SMO. The variable gain adaptive SMO is designed to estimate the speed, rotor position and stator resistance in the d–q reference frame. The active flux SMO is designed to estimate the active flux and torque in the α–β reference frame. Global asymptotic stability of the observers is guaranteed by the Lyapunov stability analysis. Finally, simulations and experiments are carried out to verify the effectiveness of the proposed control scheme.

To improve the control performance of anti-swinging and the orientation of two-dimensional bridge crane, a novel dynamic sliding mode variable structure control algorithm is presented here. The proposed controller can ensure global stability through improved design of sliding surface for the drive control force, and obtain the continuous driving control force in time domain, by using the Sigmoid function for switching function to suppress chattering. Experimental results demonstrated that it is effective on chattering suppression, swing reduction, and robust with various load qualities and friction resistances. [ABSTRACT FROM AUTHOR]

A higher-order sliding approach to control a bioreactor model is proposed by non-commensurate fractional equations. According to existing conditions and chattering reduction, a high-order sliding mode approach has been chosen to design the controller. A mathematical problem is a barrier to use the high-order sliding mode approach for fractional order systems. The contribution of the paper is to choose proper sliding surfaces. High-order sliding mode controllers have been taken in accordance with the structure of integer order system. Thus, in order for the system to apply more precise calculations, fractional systems should somehow turn to integer order. The sliding surfaces have been selected so appropriately that we can benefit from the structure of integer order controllers for fractional order system. The sliding surface in both controllers has also been the same so as to provide conditions for comparison. The model outputs are reached the desired values using two controllers. Finally, the comparison in simulations indicates that the proposed approach has a great impact on chattering reduction. [ABSTRACT FROM AUTHOR]

This paper describes the design of an interleaved sliding mode control for a multiphase synchronous buck converter, which inherits the properties of sliding mode control, operates with fixed switching frequency in the steady-state, and ensures current equalization among phases. Moreover, a power management algorithm is added in order to decide the number of active phases as function of the power load demand, thus optimizing the converter efficiency. The system uses a Master–Slave structure where each phase can actuate as the Master one in such a way that the overall system reliability is improved. Experimental results in a 1.5 kW eight-phase synchronous buck converter show that interleaving operation, robust output voltage regulation, phase current equalization, switching frequency regulation, and power management are achieved. [ABSTRACT FROM PUBLISHER]