Adaptive Variable Structure Control Research Articles

Adaptive Bipartite Consensus of Second-Order Multi-Agent Systems With Bounded Disturbances

This paper investigates distributed adaptive bipartite consensus for second-order multi-agent systems (MASs) with bounded disturbances under a signed graph. Based on adaptive variable structure control strategies, an adaptive bipartite consensus protocol is proposed, which guarantees that the bipartite consensus can be realized if the signed graph is structurally balanced and connected. Furthermore, the external disturbances are attenuated effectively by the variable structure control. And the obtained results are applied to adaptive consensus of disturbed second-order MASs under cooperative networks. Finally, a numerical simulation is presented to demonstrate the theoretical finding.

Adaptive H∞ sliding mode control of uncertain neutral‐type stochastic systems based on state observer

SummaryThis paper is focused on the problem of adaptive sliding mode control design for uncertain neutral‐type stochastic systems under a prescribed H∞ performance. A simplified state observer is put forward to estimate the unknown state variables, which could be properly incorporated for establishing a new linear‐type switching surface and the associated adaptive variable structure controller. By virtue of the adaptive control design, unknown matched perturbation and potential uncertainties can be counteracted, and the system trajectories are guaranteed to reach the predefined switching surface within finite moment in almost surely sense, and performance analysis of the closed‐loop dynamics during the sliding surface is carried out with a specified H∞ performance. At last, two illustrative examples through computer simulations are provided to verify the effectiveness and applicability of the proposed scheme.

Robust adaptive synchronization of complex network with bounded disturbances

In this paper, we investigate distributed robust adaptive synchronization for complex networked systems with bounded disturbances. We propose both average synchronization protocol and leader-following synchronization protocol based on adaptive control and variable structure control strategies. The synchronization conditions do not require any global information except a connection assumption under the adaptive control method. Furthermore, the external disturbances are attenuated effectively. Finally, we present numerical simulations to illustrate the theoretical findings.

Optimized adaptive tracking control for an underactuated vibro-driven capsule system

This paper studies the issue of adaptive trajectory tracking control for an underactuated vibro-driven capsule system and presents a novel motion generation framework. In this framework, feasible motion trajectory is derived through investigating dynamic constraints and kernel control indexes that underlie the underactuated dynamics. Due to the underactuated nature of the capsule system, the global motion dynamics cannot be directly controlled. The main objective of optimization is to indirectly control the friction-induced stick–slip motions to reshape the passive dynamics and, by doing so, to obtain optimal system performance in terms of average speed and energy efficacy. Two tracking control schemes are designed using a closed-loop feedback linearization approach and an adaptive variable structure control method with an auxiliary control variable, respectively. The reference model is accurately matched in a finite-time horizon. The key point is to define an exogenous state variable whose dynamics is employed as a control input. The tracking performance and system stability are investigated through rigorous theoretic analysis. Extensive simulation studies are conducted to demonstrate the effectiveness and feasibility of the developed trajectory model and optimized adaptive control system.

Terminal adaptive output feedback variable structure control

Based on the Lyapunov stability theorem, an adaptive output feedback variable structure control (OFVSC) scheme is proposed in this study for a class of multi-input multi-output non-linear systems with matched and mismatched perturbations to solve regulation problems. First, a switching function is designed, and the system to be controlled is decomposed into two subsystems through a linear state transformation. Then the proposed OFVSC scheme is presented. A perturbation estimation algorithm is utilised in designing the proposed control scheme in order to overcome the problem of unmeasurable states. Adaptive mechanism is also employed so that the upper bounds of perturbations as well as perturbation estimation errors are not required to be known in advance. Furthermore, the resultant control system is capable of driving all the states into zero within a finite time and guaranteeing global stability. Finally, a numerical example is given for demonstrating the feasibility of the proposed control scheme.

Simulation Analysis of Spacecraft Automatic Levelling and Equalizing Hoist Device based on Hanging Point Adjustment

In this paper, the virtual prototype of the Spacecraft Automatic Levelling and Equalizing Hoist Device based on Hanging Point Adjustment is modelled and the Automatic levelling and equalizing process is simulated. Variable structure adaptive control system is verified to be asymptotically stable under the interference of the support vehicle. Finally, through the refinement of the ductility of the sling, which is proved that the ductility of the sling has no effect on the stability, the system is proved to have good robustness.

Dynamic modeling and adaptive vibration suppression of a high-speed macro-micro manipulator

This paper presents a dynamic modeling and microscopic vibration suppression for a flexible macro-micro manipulator dedicated to high-speed operation. The manipulator system mainly consists of a macro motion stage and a flexible micromanipulator bonded with one macro-fiber-composite actuator. Based on Hamilton's principle and the Bouc–Wen hysteresis equation, the nonlinear dynamic model is obtained. Then, a hybrid control scheme is proposed to simultaneously suppress the elastic vibration during and after the motor motion. In particular, the hybrid control strategy is composed of a trajectory planning approach and an adaptive variable structure control. Moreover, two optimization indices regarding the comprehensive torques and synthesized vibrations are designed, and the optimal trajectories are acquired using a genetic algorithm. Furthermore, a nonlinear fuzzy regulator is used to adjust the switching gain in the variable structure control. Thus, a fuzzy variable structure control with nonlinear adaptive control law is achieved. A series of experiments are performed to verify the effectiveness and feasibility of the established system model and hybrid control strategy. The excited vibration during the motor motion and the residual vibration after the motor motion are decreased. Meanwhile, the settling time is shortened. Both the manipulation stability and operation efficiency of the manipulator are improved by the proposed hybrid strategy.

Robust Adaptive Variable Structure Tracking Control for Spacecraft Chaotic Attitude Motion

A continuous globally stable control algorithm is presented to track angular velocity for spacecraft chaotic attitude motion affected by external disturbances using adaptive variable structure controller. Affected by some external disturbances, the spacecraft attitude dynamics system can generate many types of chaotic motion. Once it is required that a spacecraft with chaotic attitude motion should track the other spacecraft chaotic attitude plant to achieve angular velocity synchronization, the design of a robust tracking controller becomes necessary. The controller design is based on adaptive control theory and variable structure control theory, and adopts integral sliding surface and a single vector adjusted dynamically. Numerical simulations are performed to demonstrate the effectiveness and feasibility of the proposed adaptive variable structure controller.

Adaptive control of complex systems with unknown dynamics and input constraint: Applied to a chaotic elastic beam

SummaryOwing to the limitations of system identification and modeling techniques, there is usually some unknown dynamics in the mathematical models of the complex systems. In addition, external perturbations can affect the chaotic systems' responses and may destroy the desired control purpose. Consideration of such uncertain dynamics and external fluctuations in control applications is important in research and practice. On the other hand, because of the limited operation of control actuators, most of the practical implementations of control systems are forced with some input constraints. Therefore, this paper investigates the control problem of uncertain autonomous and/or nonautonomous complex chaotic systems in the presence of input saturation. The upper bounds of the unknown dynamics, modeling uncertainties, external perturbations, and the parameters of the saturation function are assumed to be unknown in advance. To make a fast control response, an adaptive nonsingular terminal variable structure controller is proposed to assure the finite‐time stability of the equilibrium states. Rigorous stability analysis is performed to prove the correct performance of the designed control algorithm. Numerical simulations on the unified system and a chaotic elastic beam model are developed to demonstrate the usefulness of the introduced adaptive control strategy. It is worth to notice that the derived adaptive nonsmooth sliding mode approach is general and it can be easily adopted for controlling of a wide class of uncertain MIMO nonlinear systems.

Design & application of adaptive variable structure &[formula omitted] robust optimal schemes in nonlinear control of boiler-turbine unit in the presence of various uncertainties

In this article, to improve the precision, performance and robustness of an industrial boiler-turbine, two robust controllers are designed. First, a robust adaptive variable structure control scheme (RAVSC) is proposed to control a nonlinear multi-inputs multi-outputs (MIMO) model of an industrial boiler-turbine unit, in the presence of significant uncertainties and external disturbances. To guarantee the reliable performance of the RAVSC, appropriate adaption and control laws are introduced to compensate the uncertainties and modeling imprecisions and guarantee the convergence to the sliding surface. Then, the robustness and stability of the proposed RAVSC is proved via Lyapunov stability theory. Moreover, a robust H∞ controller is designed based on μ−DKiteration , with assumption of presence rational deviation in parameters and suitable weights to attenuate the control signals. To investigate the performance of proposed control schemes, simulation studies are carried out on nonlinear dynamic model in the presence of various uncertainties. Then, the performance of designed robust controllers exposed to discussion which reveals the satisfactory performance of the both proposed controllers. However, it is observed that RAVSC has some minor advantages over the robust H∞ controller.

Dual-stage adaptive finite-time modified function projective multi-lag combined synchronization for multiple uncertain chaotic systems

Abstract In this paper, for multiple different chaotic systems with unknown bounded disturbances and fully unknown parameters, a more general synchronization method called modified function projective multi-lag combined synchronization is proposed. This new method covers almost all of the synchronization methods available. As an advantage of the new method, the drive system is a linear combination of multiple chaotic systems, which makes the signal hidden channels more abundant and the signal hidden methods more flexible. Based on the finite-time stability theory and the sliding mode variable structure control technique, a dual-stage adaptive variable structure control scheme is established to realize the finite-time synchronization and to tackle the parameters well. The detailed theoretical derivation and representative numerical simulation is put forward to demonstrate the correctness and effectiveness of the advanced scheme.

Improved adaptive backstepping sliding mode control for generator steam valves of non‐linear power systems

The stability problem of steam valves in a single machine infinite bus system with thyristor controlled series compensation is addressed through the use of an improved adaptive backstepping method based on error compensation. The method combines sliding mode variable structure control, backstepping control and adaptive control. Initially, an excitation control input and error compensation are simultaneously obtained in the design of virtual control by adaptive backstepping and the Lyapunov method. The Lyapunov function is then constituted in stages to achieve subsystem stability, before obtaining a parameter updating law and a non-linear control law for the closed-loop system. The results for both systems show that the improved non-linear backstepping sliding mode variable structure control approach can have four benefits. It can ensure that the system states are bounded, retain the faster stability of power systems, improve the speed of parameter identification and achieve real-time parameter estimation. Finally, a simulation is presented to illustrate both the effectiveness and the feasibility of the improved control approach.

A robust adaptive fuzzy variable structure tracking control for the wheeled mobile robot: Simulation and experimental results

In this paper an adaptive fuzzy variable structure control (kinematic control) integrated with a proportional plus derivative control (dynamic control) is proposed as a robust solution to the trajectory tracking control problem for a differential wheeled mobile robot. The variable structure controller, based on the sliding mode theory, is a well known, proven control method, fit to deal with uncertainties and disturbances (e.g., structural and parameter uncertainties, external disturbances and operating limitations). To minimize the problems found in practical implementations of the classical variable structure controllers, an adaptive fuzzy logic controller replaces the discontinuous portion of the control signals (avoiding the chattering), causing the loss of invariance, but still ensuring the robustness to uncertainties and disturbances without having any a priori knowledge of their boundaries. Moreover, the adaptive fuzzy logic controller is a feasible tool to approximate any real continuous nonlinear system to arbitrary accuracy, and has a simple structure by using triangular membership functions, a low number of rules that must be evaluated, resulting in a lower computational load for execution, making it feasible for real time implementation. Stability analysis and the convergence of tracking errors as well as the adaptation laws are guaranteed with basis on the Lyapunov theory. Simulation and experimental results are explored to show the verification and validation of the proposed control strategy.

Dynamical adaptive integral backstepping variable structure controller design for uncertain systems and experimental application

SummaryIn this study, a dynamical adaptive integral backstepping variable structure control (DAIBVSC) system based on the Lyapunov stability theorem is proposed for the trajectory tracking control of a nonlinear uncertain mechatronic system with disturbances. In this control scheme, no prior knowledge is required on the uncertain parameters and disturbances because it is estimated by two types of dynamical adaptive laws. These adaptive laws are integrated into the dynamical adaptive integral backstepping control and variable structure control (VSC) parts of the DAIBVSC. The dynamical adaptive law in the dynamical adaptive integral backstepping control part updates parametric uncertainties, while the other in the VSC part adapts upper bounds of non‐parametric uncertainties and disturbances. In order to achieve a more robust output tracking and better parameter adaptation, the control system is extended by one integrator and sliding surface is augmented by an integral action. Experimental evaluation of the DAIBVSC is conducted with respect to performance and robustness to parametric uncertainties. Experimental results of the DAIBVSC are compared with those of a traditional VSC. The proposed DAIBVSC exhibits satisfactory output tracking performance, good estimation of the uncertain parameters and can reject disturbances with a chattering free control law. Copyright © 2017 John Wiley & Sons, Ltd.

Adaptive variable structure control of input delay non-minimum phase hypersonic flight vehicles

An adaptive variable structure control strategy is proposed for the output tracking control of input delay non-minimum hypersonic flight vehicles. The problem is challenging because of the complex nonlinearity of hypersonic flight vehicles and the existence of input delay. The nonlinear model of hypersonic flight vehicles is partially linearized, and a state tracking model is constructed based on the ideal internal dynamics of hypersonic flight vehicles. A filtered tracking error is introduced to handle the input delay. A variable structure control strategy is proposed for the stability of filtered tracking error system, and an adaptive law is established for the unknown perturbations. Finally, the effectiveness of the proposed control method is shown by the simulation results.

Robust Adaptive Coordination Controller for a Spacecraft Equipped with a Robotic Manipulator

Free-flying robotic spacecraft play a significant role in the space industry today. Unlike ground-based robots, the manipulator motion in a space robot can cause undesirable disturbances to the spacecraft platform, causing its attitude to change, potentially disrupting communication and solar energy collection processes as a result. Thus, coordinated control of both the spacecraft attitude and the manipulator motion become essential for successful space operations. Though past research has developed dynamic models for spacecraft manipulators, the contribution of reaction wheels to the angular momentum of the entire system needs further consideration. This paper reformulates the dynamic equations of a free-flying space robot by taking the aspect of reaction wheels into account. A diagonalization method is introduced to decouple the highly nonlinear multi-input/multi-output system model. A novel adaptive variable structure control method is then applied to implement a robust coordination controller for the space robot subjected to system uncertainties. Simulations are carried out on a spacecraft model with a 3-degree-of-freedom manipulator mounted on it to demonstrate the robustness of the proposed approach. Comparisons with sliding mode control show that the new controller results in faster settling times, which leads to maintaining uninterrupted communication links and efficient solar energy harvesting.

An adaptive variable structure control of the robot satellite system with floating base in Cartesian space

Aiming at the non-parametric and time-varying parametric uncertainty problems such as the external disturbances, smooth parameter variations and jump parameter changes existing in the robot satellite system with floating base, an adaptive variable structure trajectory tracking control method in Cartesian space is proposed. The dynamics equation in joint space of the robot satellite system with floating base is established based on the extended manipulator model, and the dynamics model of the system in Cartesian space is derived considering external disturbances to the manipulator and the base simultaneously. An adaptive variable structure controller is designed by adopting the composite adaptive control combined with variable structure control under the condition that the bounds of external disturbances and parameter variations are unknown, and the robustness analysis of the controller is performed. The simulation of a two-link planar robot satellite system with floating base adopting the control method presented is implemented. The simulation result shows that the end-effector of the robot satellite with floating base has a good capability of trajectory tracking in Cartesian space.

Adaptive Variable Structure Control for Mismatched Uncertain Systems

This paper proposes an adaptive variable structure control (VSC) for a class of mismatched uncertain systems with unknown disturbances. First, a necessary and sufficient condition in terms of linear matrix inequalities is proposed to guarantee the system in sliding mode is asymptotically stable. Second, an adaptive output feedback variable structure controller is designed to force the system states reach the sliding surface and stay on it thereafter. Finally, the advantages and effectiveness of the proposed approaches are demonstrated via a numerical example.

H infinity control design for Eight-Rotor MAV attitude system based on identification by interval type II fuzzy neural network

In order to overcome the influence of system stability and accuracy caused by uncertainty, estimation errors and external disturbances in Eight-Rotor MAV, L2 gain control method was proposed based on interval type II fuzzy neural network identification here. In this control strategy, interval type II fuzzy neural network is used to estimate the uncertainty and nonlinearity factor of the dynamic system, the adaptive variable structure controller is applied to compensate the estimation errors of interval type II fuzzy neural network, and at last, L2 gain control method is employed to suppress the effect produced by external disturbance on system, which is expected to possess robustness for the uncertainty and non-linearity. Finally, the validity of the L2 gain control method based on interval type II fuzzy neural network identifier applied to the Eight-Rotor MAV attitude system has been verified by three prototy experiments.

Stability analysis of a combined direct variable structure adaptive control – the discrete‐time case

SummaryThis paper presents the proofs of robust stability of a discrete‐time robust model reference controller combined with variable structure in an adaptive framework. All the proofs of robust stability are derived for the discrete‐time case and are similar to those already existing for the conventional non‐combined case. The controller is applied to a SISO LTI plant with unmodeled dynamics of multiplicative and additive types. It is shown that the combined controller can arbitrarily improve the convergence of the error while maintaining the robustness if compared with the non–combined case. Simulation results illustrate the performance of the proposed control strategy. Copyright © 2016 John Wiley & Sons, Ltd.