Switching signal design for asymptotic stability of uncertain multiple equilibrium switched systems with actuator saturation

This paper addresses the problem of robust control for a class of multiple equilibrium switched systems with actuator saturation and parameter uncertainties. The parameter uncertainties are described in norm‐bounded form. By combining the parametric Lyapunov equation approach and the gain‐scheduling technique, stabilization conditions are established in terms of linear matrix inequalities. State‐feedback controllers can be designed to guarantee the robust stability and performance of the closed‐loop system in the presence of parameter uncertainties and actuator saturation. The proposed method is to increase the convergence rate during the convergence of the states. Numerical examples and simulations are worked out to illustrate the feasibility of the proposed results. Copyright © 2015 John Wiley & Sons, Ltd.     

Fault‐tolerant formation control of multiple UAVs in the presence of actuator faults

In order to counteract actuator faults in formation flight of multiple unmanned aerial vehicles (UAVs), this paper presents a fault‐tolerant formation control (FTFC) design methodology, in which the reference generator and the finite‐time convergence of FTFC gains are explicitly considered. Feasible references in response to actuator faults can be generated by considering the health and mission conditions of an overall team of UAVs. Moreover, by applying an auxiliary integrated regressor matrix and vector method, FTFC gains can converge within a finite amount of time to facilitate the fault accommodation process. Thus, the negative effects resulting from failed actuators can be compensated by the healthy/redundant actuators in UAVs. Simulation studies of UAV formation flight are carried out to exemplify the effectiveness of this design approach. Copyright © 2015 John Wiley & Sons, Ltd.     

Stabilization on null controllable region of delta operator systems subject to actuator saturation

This paper focuses on stabilization on null controllable region of delta operator systems subject to actuator saturation via constructing suitable controllers. Under a saturated linear feedback law, a set of stable equilibrium points is obtained for the delta operator system with actuator saturation. A comprehensive controller is given to show global stabilization of the delta operator system. Thereby, semi‐global stabilization of the delta operator system is also achieved. For higher‐order systems with no more than two unstable exponentially poles, a new feedback law is constructed to achieve semi‐global stabilization on the null controllable region. Finally, three examples are given to illustrate the effectiveness of the proposed techniques. Copyright © 2016 John Wiley & Sons, Ltd.     

Input‐output based fault estimation for linear systems with partially dynamic uncertainty and actuator faults

This paper is concentrated on the problem of fault estimation for a class of linear systems with partially dynamic uncertainty and actuator faults. A novel input–output‐based fault estimation approach is proposed, by which the estimates can asymptotically converge to the magnitudes of the actuator faults, and the asymptotic convergence of the estimation is theoretically proved. Some important properties related to the corresponding fault errors are obtained. The proposed input–output‐based fault estimation method can exponentially weaken the effects of the fault derivatives on the fault error dynamics. Based on the online estimates, a corresponding robust fault‐tolerant control policy is designed, so that the closed‐loop system is asymptotically stable and the control output curves can asymptotically trace to the normal control output curves. Finally, three examples are given to show the effectiveness, merits, and applications of the proposed methods. Copyright © 2016 John Wiley & Sons, Ltd.     

偏置磁场对超磁致伸缩致动器输出特性的影响分析

采用Terfenol-D棒作为超磁致伸缩致动器GMA(Giant Magnetostrictive Actuator)的主要材料,研制了有偏置磁场和无偏置磁场两种超磁致伸缩致动器,分析了具有分段式永磁偏置和无偏置致动器的结构及性能.基于安培定律、磁路基尔霍夫定律、叠加原理对致动器的磁场进行理论分析.为进一步分析磁场分布,创建三维模型,利用有限元仿真软件对GMA内部磁场进行分析和比较,仿真结果表明:分段式永磁偏置结构致动器能够达到理想的偏置要求,无磁场偏置的致动器在电流作用下磁场分布更均匀.实验结果表明:超磁致伸缩致动器输出位移和力的大小分别与Terfenol-D棒长度、直径呈正相关,施加偏置磁场能够改善超磁致伸缩致动器的动静态输出特性,提高致动器静态输出位移和力的线性度,消除动态输出位移与输出力的倍频现象,提高其输出精度.     

Delay‐dependent fault‐tolerant controller for time‐delay systems with randomly occurring uncertainties

This paper addresses the passivity‐based control problem for a class of time‐varying delay systems subject to nonlinear actuator faults and randomly occurring uncertainties via fault‐tolerant controller. More precisely, the uncertainties are described in terms of stochastic variables, which satisfies Bernoulli distribution, and the existence of actuator faults are assumed not only linear but also nonlinear, which is a more general one. The main objective of this paper is to design a state feedback‐reliable controller such that the resulting closed‐loop time‐delay system is stochastically stable under a prescribed mixed and passivity performance level γ>0 in the presence of all admissible uncertainties and actuator faults. Based on Lyapunov stability method and some integral inequality techniques, a new set of sufficient conditions is obtained in terms of linear matrix inequality (LMI) constraints to ensure the asymptotic stability of the considered system. Moreover, the control design parameters can be computed by solving a set of LMI constraints. Finally, two examples including a quarter‐car model are provided to show the efficiency and usefulness of the proposed control scheme. Copyright © 2017 John Wiley & Sons, Ltd.     

Adaptive finite‐time fault‐tolerant tracking control for a class of MIMO nonlinear systems with output constraints

In this work, we present a novel adaptive finite‐time fault‐tolerant control algorithm for a class of multi‐input multi‐output nonlinear systems with constraint requirement on the system output tracking error. Both parametric and nonparametric system uncertainties can be effectively dealt with by the proposed control scheme. The gain functions of the nonlinear systems under discussion, especially the control input gain function, can be not fully known and state‐dependent. Backstepping design with a tan‐type barrier Lyapunov function and a new structure of stabilizing function is presented. We show that under the proposed control scheme, finite‐time convergence of the output tracking error into a small set around zero is guaranteed, while the constraint requirement on the system output tracking error will not be violated during operation. An illustrative example on a robot manipulator model is presented in the end to further demonstrate the effectiveness of the proposed control scheme. Copyright © 2016 John Wiley & Sons, Ltd.     

Overall convergence rate of delta operator systems subject to actuator saturation

In this paper, overall convergence rate is considered for a delta operator system with actuator saturation. A saturation feedback law is presented for the delta operator system to obtain a desired overall convergence rate. Some properties on the overall convergence rate are revealed for time‐optimal actuator saturation delta operator systems. Limitations on the overall convergence rate are also investigated by proposed methods. An optimization problem is solved through a linear matrix inequality method to obtain the domain of attraction and overall convergence rate. Two numerical examples are provided to demonstrate the effectiveness of the proposed techniques. Copyright © 2017 John Wiley & Sons, Ltd.     

Approximation Optimal Vibration for Networked Nonlinear Vehicle Active Suspension with Actuator Time Delay

This paper is concerned with the modelling and vibration control problem for networked nonlinear vehicle active suspension (NNVAS) with actuator time delay. Inserting in‐vehicle communication network to active suspension, a novel model for NNVAS is established based on the Takagi‐Sugeno fuzzy fusion technology first. By introducing a transformation vector, NNVAS with actuator time delay is reformed as a delay‐free nonlinear system. Then, an approximation optimal vibration controller (AOVC) is proposed by using an iterative algorithm, which consists of suspension state item, a road disturbance state item, and a compensated item for nonlinear response. Dependant on the control performance in each iteration, the computability of proposed AOVC is realized. A reduced‐order observer is designed to solve the physical unrealizable problem of road disturbances. Finally, compared with the open‐loop system and control scheme without network setting, the capability of improving control performance under AOVC is illustrated.     

Robust MPC for Linear Systems with Structured Time‐Varying Uncertainties and Saturating Actuator

In this paper, a synthesis of model predictive control (MPC) algorithm is presented for uncertain systems subject to structured time‐varying uncertainties and actuator saturation. The system matrices are not exactly known, but are affine functions of a time varying parameter vector. To deal with the nonlinear actuator saturation, a saturated linear feedback control law is expressed into a convex hull of a group of auxiliary linear feedback laws. At each time instant, a state feedback law is designed to ensure the robust stability of the closed‐loop system. The robust MPC controller design problem is formulated into solving a minimization problem of a worst‐case performance index with respect to model uncertainties. The design of controller is then cast into solving a feasibility of linear matrix inequality (LMI) optimization problem. Then, the result is further extended to saturation dependent robust MPC approach by introducing additional variables. A saturation dependent quadratic function is used to reduce the conservatism of controller design. To show the effectiveness, the proposed robust MPC algorithms are applied to a continuous‐time stirred tank reactor (CSTR) process.