Adaptive Leader-Follower Consensus Control of Multiple Flexible Manipulators With Actuator Failures and Parameter Uncertainties

In this paper,the leader-follower consensus problem for a multiple flexible manipulator network with actuator failures,parameter uncertainties,and unknown time-varying boundary disturbances is addressed.The purpose of this study is to develop distributed controllers utilizing local interactive protocols that not only suppress the vibration of each flexible manipulator but also achieve consensus on joint angle position between actual followers and the virtual leader.Following the accomplishment of the reconstruction of the fault terms and parameter uncertainties,the adaptive neural network method and parameter estimation technique are employed to compensate for unknown items and bounded disturbances.Furthermore,the Lyapunov stability theory is used to demonstrate that followers’angle consensus errors and vibration deflections in closed-loop systems are uniformly ultimately bounded.Finally,the numerical simulation results confirm the efficacy of the proposed controllers.

Robust fault-tolerant controller design for linear time-invariant systems with actuator failures:an indirect adaptive method

In this paper,indirect adaptive state feedback control schemes are developed to solve the robust fault-tolerant control （FTC） design problem of actuator fault and perturbation compensations for linear time-invariant systems.A more general and practical model of actuator faults is presented.While both eventual faults on actuators and perturbations are unknown,the adaptive schemes are addressed to estimate the lower and upper bounds of actuator-stuck faults and perturbations online,as well as to estimate control effectiveness on actuators.Thus,on the basis of the information from adaptive schemes,an adaptive robust state feed-back controller is designed to compensate the effects of faults and perturbations automatically.According to Lyapunov stability theory,it is shown that the robust adaptive closed-loop systems can be ensured to be asymptotically stable under the influence of actuator faults and bounded perturbations.An example is provided to further illustrate the fault compensation effectiveness.

Robust reliable H_∞ control for discrete-time Markov jump linear systems with actuator failures

The robust reliable H∞ control problem for discrete-time Markovian jump systems with actuator failures is studied. A more practical model of actuator failures than outage is considered. Based on the state feedback method, the resulting closed-loop systems are reliable in that they remain robust stochastically stable and satisfy a certain level of H∞ disturbance attenuation not only when all actuators are operational, but also in case of some actuator failures, The solvability condition of controllers can be equivalent to a feasibility problem of coupled linear matrix inequalities （LMIs）. A numerical example is also given to illustrate the design procedures and their effectiveness.

A parameter estimation based adaptive actuator failure compensation control scheme

An adaptive actuator failure compensation control scheme is developed using an indirect adaptive control method,by calculating the controller parameters from adaptive estimates of system parameters and actuator failure parameters.A key technical issue is how to deal with the actuator failure uncertainties such as failure pattern,time and values.A complete parametrization covering all possible failures is used to solve this issue for adaptive parameter estimation.A simultaneous mapping from the estimated system/failure parameters to the controller parameters is employed to make the control system capable of ensuring the desired system performance under failures,which is verified by simulation results.

Adaptive actuator failure compensation and disturbance rejection scheme for spacecraft

An adaptive actuator failure compensation scheme is proposed for attitude tracking control of spacecraft with unknown disturbances and uncertain actuator failures. A new feature of this adaptive control scheme is the adaptation of the failure pattern parameter estimates, as well as the failure signal parameter estimates, for direct adaptive actuator failure compensation. Based on an adaptive backstepping control design, the estimates of the disturbance parameters are used to solve the disturbance rejection problem. The unknown disturbances are compensated completely with the stability of the whole closed-loop system. The scheme is not only able to accommodate uncertain actuator failures, but also robust against unknown external disturbances. Simulation results verify the desired adaptive actuator failure compensation performance.

A Robust Roll Stabilization Controller with Aerodynamic Disturbance and Actuator Failure Consideration

Combining adaptive theory with an advanced second-order sliding mode control algorithm,a roll stabilization controller with aerodynamic disturbance and actuator failure consideration for spinning flight vehicles is proposed in this paper.The presented controller is summarized as an“observer-controller”system.More specifically,an adaptive secondorder sliding mode observer is presented to select the proper design parameters and estimate the knowledge of aerodynamic disturbance and actuator failure,while the proposed roll stabilization control scheme can drive both roll angle and rotation rate smoothly converge to the desired value.Theoretical analysis and numerical simulation results demonstrate the effectiveness of the proposed controller.

Adaptive fault-tolerant control of high-speed maglev train suspension system with partial actuator failure: design and experiments

High-speed maglev trains will play an important role in the high-speed transportation system in the near future.However,under the conditions of strong magnetic fields and continuous operation,the actuators of the high-speed maglev train suspension system are prone to lose partial effectiveness,which makes the suspension control problem challenging.In addition,most existing fault-tolerant control(FTC)methods for suspension systems require linearization around the equilibrium points during the controller design or stability analysis.Therefore,from a practical perspective,this study presents a novel nonlinear FTC strategy with adaptive compensation for high-speed maglev train suspension systems.First,a nonlinear dynamic model of the suspension system based on join-structure is established and the actuator failures are described.Then,a nonlinear fault-tolerant suspension control law with an adaptive update law is designed to achieve stable suspension against partial actuator failure.The Lyapunov theory and extended Barbalat lemma are utilized to rigorously prove the closed-loop asymptotic stability even if there is partial actuator failure,without any approximation to the original nonlinear dynamics.Finally,hardware experimental results are included to demonstrate the effectiveness of the proposed approach.

Piecewise model-based adaptive compensation control for high-speed trains with unknown actuator failures

In order to deal with the uncertainties caused by different operation conditions and unknown actuator failures of high-speedtrains,an adaptive failures compensation control scheme is designed based on the piecewise model.A piecewise constant model is introduced to describe the variable system parameters caused by the variable operation environments,and a multiple-particle plecewise model of high-speed trains,with unknown actuator failures,is then established.An adaptive failure compensation controller is developed for the multiple-particle piecewise constant model,by using a direct model refering to the adaptive control method.Such an adaptive controller can not only compensate the uncertainties from unknown actuator failures,but also effectively deal with the uncertainties caused by different operating conditions.Finally,a CRH380A high-speed train model is taken as the controlled object for the simulation study.The simulation results show that the proposed controller ensures the desired system performance in the presence of unknown actuator failures and uncertain operation conditions.

Postcapture stabilization of space robots considering actuator failures with bounded torques

Space robotics is regarded as one of the most impressing approaches for space debris removal missions. Due to the residual momentum of debris, it is essential to stabilize the base rapidly after capture. This paper presents a novel control strategy for stabilization of a space robot in postcapture considering actuator failures and bounded torques. In the control strategy, the motion of the manipulator is not regarded as a disturbance to the base; in contrast, it is utilized to compensate for the limitation of the control torques by means of an inverse dynamical model of the system. Different scenarios where actuators are external mechanisms or momentum exchange devices have been carried out, and for actuator failures, both single-and two-actuator failures have been considered. Regarding to the performance of actuators, control torques are bounded. In cases that either single or two actuators have failed, the base can be stabilized kinematically when actuators are external mechanisms, but can only be stabilized dynamically when only momentum exchange devices are used. Finally, a space robot with a seven-degree-of-freedom manipulator in postcapture is studied to verify the validity and feasibility of the proposed control scheme. Simulation results show that the whole system can be stabilized rapidly.

Robust stability analysis of switched uncertain systems with multiple time-varying delays and actuator failures

In this paper,the robust stability issue of switched uncertain multidelay systems resulting from actuator failures is considered.Based on the average dwell time approach,a set of suitable switching signals is designed by using the total activation time ratio between the stable subsystem and the unstable one.It is first proven that the resulting closed-loop system is robustly exponentially stable for some allowable upper bound of delays if the nominal system with zero delay is exponentially stable under these switching laws.Particularly,the maximal upper bound of delays can be obtained from the linear matrix inequalities.At last,the effectiveness of the proposed method is demonstrated by a simulation example.

Direct adaptive actuator failure compensation control:a tutorial

A resilient control system is expected to have the capacity to restore the desired system stability and tracking performance in the presence of uncertain system faults such as actuator failures.While redundant actuators are used for actuator failure accommodation,uncertain actuator failures,whose failure time,pattern,and values may be unknown,can bring new challenges to feedback control design as such uncertain failures can introduce large structural,parametric,and actuation uncertainties.Two technical issues are associated with using redundant actuators:how redundant actuators should be coordinated for effective failure compensation control,and how a feedback control law should be adaptively designed to compensate uncertain actuator failures.In this paper,we present a tutorial on direct adaptive failure compensation-based solutions to these issues for different types of control systems:state tracking using state feedback,output tracking using state feedback or output feedback,for linear,non-linear,and multi-input multi-output systems.We give an overview on such adaptive actuator failure compensation designs which have special capacities to effectively use actuation redundancy to handle uncertain actuator failures,using either direct or indirect adaptive control approaches for direct adaptive actuator failure compensation without explicit failure detection,for fast and effective failure accommodation.

STABILITY ANALYSIS OF DECENTRALIZED ADAPTIVE BACKSTEPPING CONTROL SYSTEMS WITH ACTUATOR FAILURES

In this paper,the authors analyze the stability of a class of interconnected systems withsubsystem unmodeled dynamics and dynamic interactions employing decentralized adaptive controllersdesigned by Wen,Zhou,and Wang (2008) in the presence of actuator failures.It will be shown that theglobal stability of the remaining closed-loop system is still ensured and the outputs are also regulatedto zero when some subsystems break down.

Adaptive Output Feedback Control Using Fault Compensation and Fault Estimation for Linear System with Actuator Failure

The problem of linear systems subject to actuator faults（outage,loss of efectiveness and stuck）,parameter uncertainties and external disturbances is considered.An active fault compensation control law is designed which utilizes compensation in such a way that uncertainties,disturbances and the occurrence of actuator faults are account for.The main idea is designing a robust adaptive output feedback controller by automatically compensating the fault dynamics to render the close-loop stability.According to the information from the adaptive mechanism,the updating control law is derived such that all the parameters of the unknown input signal are bounded.Furthermore,a disturbance decoupled fault reconstruction scheme is presented to evaluate the severity of the fault and to indicate how fault accommodation should be implemented.The advantage of fault compensation is that the dynamics caused by faults can be accommodated online.The proposed design method is illustrated on a rocket fairing structural-acoustic model.

Robust Adaptive Actuator Failure Compensation for a Class of Uncertain Nonlinear Systems

This paper presents a robust adaptive state feedback control scheme for a class of parametric-strict-feedback nonlinear systems in the presence of time varying actuator failures. The designed adaptive controller compensates a general class of actuator failures without any need for explicit fault detection. The parameters, times, and patterns of the considered failures are completely unknown. The proposed controller is constructed based on a backstepping design method. The global boundedness of all the closed-loop signals is guaranteed and the tracking error is proved to converge to a small neighborhood of the origin. The proposed approach is employed for a two-axis positioning stage system as well as an aircraft wing system. The simulation results show the correctness and effectiveness of the proposed robust adaptive actuator failure compensation approach.

Reliable control of discrete-time linear systems with actuator failure

A sufficient condition is given for robust stability of a discrete linear system in which an arbitrary portion of input channel is permanently attenuated or disconnected due to actuator fault.The partial disconnection/attenuation of the control input,is modelled as uncertainty and dealt with via a robust control method.The proposed method enables one to design a controller in such a way that the closed loop system remains stable when any combination of input signals is disconnected if the open loop system is stable and fulfils some additional properties.It is shown that the linear quadratic regulator can guarantee reliable closed loop with some specific choices for weighting matrices.The result is extended to unstable systems by assuming additional constraints on the failed actuators.Compared to previously established results,the proposed conditions are easier to verify and applicable to a wider class of systems.An example is also included.

ADAPTIVE TRACKING CONTROL FOR ACTUATOR FAILURE COMPENSATION BASED ON MT-FILTERS

This paper considers the problem of actuator failure compensation for a class of nonlinearsystems in the form of output-feedback.MT-filters are exploited to estimate the unmeasured states.The backsteppping technique is used to construct the controller recursively.The proposed compensationscheme can grantee the boundedness of all the closed-loop signals and asymptotic output tracking.Thetheoretical results are illustrated by a simulation example.

Non-fragile robust H_(∞)control of nonlinear networked control systems with time-varying delay and unknown actuator failures

Purpose-This paper is concerned with non-fragile robust H_(∞)control problems for nonlinear networked control systems(NCSs)with time-varying delay and unknown actuator failures.The paper aims to discuss these issues.Design/methodology/approach-The system parameters are allowed to have time-varying uncertainties and the actuator faults are unknown but whose upper and lower bounds are known.By using some lemmas,uncertainties can be replaces with the known values.By taking the exogenous disturbance and network transmission delay into consideration,a delay nonlinear system model is constructed.Findings-Based on Lyapunov stability theory,linear matrix inequalities(LMIs)and free weighting matrix methods,the sufficient conditions for the existence of the non-fragile robust H_(∞)controller gain are derived and which can obtained by solving the LMIs.Finally,a numerical example is provided to illustrate the effectiveness of the proposed methods.Originality/value-The introduced approach is interesting for NCSs with time-varying delay and unknown actuator failures.

Event-triggered robust control for networked control systems with actuator failures and time-varying transmission delays

Purpose–The purpose of this paper is with robust control problem for event-triggered networked control systems(NCSs)with actuator failures and time-varying transmission delays.Design/methodology/approach–A random sequence is introduced to describe the actuator faults,and a novel event-triggering communication scheme is adopted in the sensor-to-controller channel.By taking the event-triggered mechanism and network transmission delay into consideration,a delay system model is constructed.Findings–Based on Lyapunov stability theory and free weighting matrix method,the feasibility criteria for co-designing both the controller gain and the trigger parameters are derived.Finally,a simulation example is exploited to demonstrate the effectiveness of the proposed linear matrix inequalities(LMIs)approach.Originality/value–The introduced approach is interesting for NCSs with actuator failures and timevarying transmission delays.

Adaptive controller design for uncertain singular systems with actuator failure

In this paper,the problem of model reference adaptive controller design with actuator failure is solved for a series of uncertain singular systems.The research on partial actuator failure is relatively mature and it is necessary to solve the problem of how to guarantee the system performance when the actuator fails completely.For this reason,we treat the system with actuator failure as a switching system with two subsystems and then solve the stability analysis problem of the error switching system.The emphasis is to design the adaptive controller by some sufficient linear matrices inequalities(LMIs)conditions and obtain the global stability criterion of the error switching system through the resident time method.Finally,the proposed method is applied to HiMAT aircraft to illustrate the feasibility and effectiveness of this kind of problem.

Adaptive failure compensation for uncertain systems with multiple inputs

The aim of this paper is to develop controllers for uncertain systems in the presence of stuck type actuator failures.A new scheme is proposed to design output feedback controllers for a class of uncertain systems having redundant control inputs,with which the relative degrees of transfer functions are different.To deal with these inputs using backstepping technique,a pre-filter is introduced before each actuator such that its output is the input to the actuator.The orders of the pre-filters are chosen properly to ensure all their inputs can be designed at the same step in the systematic design.To compensate for the effects of possible failed actuators,more uncertain parameters than system parameters are required to be identified.With the proposed scheme,the global boundedness of the closed-loop system can still be ensured and the system output can be regulated to a specific value when some of the actuators＇ outputs are stuck at unknown fixed values.