Search

The study addresses the consensus problem of linear time invariant (LTI) multi‐agent systems with constant input delay and matched external disturbances by using relative output information. First, distributed disturbance observers are constructed to estimate the disturbances generated by linear exosystems with unknown initial conditions. Next, a disturbance observer‐based predictor feedback control law is developed for each agent to realise consensus disturbance rejection in the presence of input delay. Then, a linear matrix inequality‐based control design algorithm is given to determine the satisfactory control parameters. It is proved that state consensus can be achieved for both leaderless and leader–follower networks in the presence of large input delay and matched disturbances under the control scheme. Finally, a simulation example is provided to validate the theoretical results. [ABSTRACT FROM AUTHOR]

This study proposes an adaptive non‐singular integral terminal sliding mode control (ANITSMC) scheme for trajectory tracking of autonomous underwater vehicles (AUVs) with dynamic uncertainties and time‐varying external disturbances. The ANITSMC is first proposed for a first‐order uncertain non‐linear dynamic system to eliminate the singularity problem in conventional terminal sliding mode control (TSMC) and avoid the requirement of the bound information of the lumped system uncertainty. The time taken to reach the equilibrium point from any initial error is guaranteed to be finite. The proposed ANITSMC is then applied to trajectory tracking control of AUVs. It guarantees that the velocity tracking errors locally converge to zero in finite time and after that the position tracking errors locally converge to zero exponentially. The designed ANITSMC of AUVs avoids the requirement of the prior knowledge of the lumped system uncertainty bounds as opposite to the existing globally finite‐time stable tracking control (GFTSTC), provides higher tracking accuracy than the existing GFTSTC and adaptive non‐singular TSMC (ANTSMC) and offers faster convergence rate and better robustness against dynamic uncertainties and time‐varying external disturbances than the adaptive proportional‐integral sliding mode control (APISMC). Comparative simulation results are presented to validate the superiority of the ANITSMC over the APISMC. [ABSTRACT FROM AUTHOR]

An optimal disturbance rejection controller design method is put forward analytically for the synchronised output regulation of time‐delayed multi‐agent systems (MAS). All kinds of linear MAS can be described by a novel block diagram based on transfer functions in a unified framework. For each subsystem without intercommunication, the optimal output, input and balancing output–input load disturbance rejection controllers are designed independently. A filter is used to be in series with each controller to not only stabilise the whole systems but also achieve a tradeoff between nominal performance and robustness by adjusting a single tuning parameter. The proposed distributed H2 controllers calculated by algebraic solution perform better capacity of disturbance attenuation than the conventional given‐structured protocols. Two simulation examples demonstrate the validity of the new algorithm. [ABSTRACT FROM AUTHOR]

Cooperative output regulation is a general framework, which considers output synchronisation, homogenisation and disturbance rejection simultaneously. To be an extension, this study divides the lumped disturbance into two parts, namely, local disturbance which is slow‐varying, mismatched and non‐linear, and global disturbance generated by an autonomous linear system. Generalised extended state observers (GESOs) are constructed to estimate the local states, the local disturbances and the global disturbance simultaneously. Observer‐based controllers are designed to realise cooperative output regulation in the presence of mismatched uncertainties. In control design, a linear matrix inequality‐based design methodology is proposed to get the exponentially convergent GESO with guaranteed decay rate. A simulation example is then shown to validate the theoretical results. [ABSTRACT FROM AUTHOR]

In this study, the authors mainly focus on the event‐triggered control design problem of networked control systems (NCSs) with dynamic quantisation and fault. The research contents are divided into two parts. The first part assumes that quantised measurements of the state are available, asymptotic stability analysis and feedback controller design of the event‐triggered NCSs with constant sensor fault and actuator fault are accomplished. The second part assumes that quantised measurements of the input are available, stochastic actuator fault, which is modelled by the Bernoulli distributed white sequence is considered in this situation, and a robust feedback controller is designed. At the end, numerical examples are given to illustrate the effectiveness of the obtained results. [ABSTRACT FROM AUTHOR]

This study addresses the finite‐frequency robust feedback controller design problem against actuator faults for linear parameter‐varying systems. First, a general model of actuator faults is presented. Then, sufficient conditions for the existence of the state‐feedback controller are obtained by using generalised Kalman–Yakubovich–Popov lemma and projection lemma, which guarantee that the closed‐loop system satisfies robustness performance in a finite‐frequency domain and is stable for both faults free and actuator faults. In addition, by introducing a state feedback gain, the non‐convexity conditions of the output‐feedback gain are derived. An iterative linear matrix inequality algorithm is proposed in this study to get the solution. The performances of the proposed reliable controller schemes are illustrated by two examples. [ABSTRACT FROM AUTHOR]

In this study, the authors investigate distributed model predictive control for polytopic uncertain systems subject to actuator saturations and packet dropouts with time‐varying probabilities in controller‐to‐actuator channels. For the sake of less computational efforts and a flexible system structure, the global system is decomposed into several lower‐dimensional subsystems and the subsystems optimise a global performance function in parallel. A novel augmented distributed controller model is proposed to describe both the actuator saturations and packet dropouts in one unified expression by adopting a stochastic variable taking the value 1 or 0 with time‐varying probabilities and accordingly a new result is obtained. By placing the saturated linear feedback law into the convex hull of a group of linear feedback laws, the distributed controller for each subsystem is obtained from the solution of the convex optimisation problem involving linear matrix inequalities. A numerical example is supplied to demonstrate the effectiveness of the developed techniques. [ABSTRACT FROM AUTHOR]

Output regulation is a general framework, for it not only can achieve closed‐loop stability, but also can realise asymptotic tracking and disturbance rejection. Within this framework, the authors consider the containment problem of heterogeneous linear multi‐agent systems with directed graphs. Via dynamic compensator techniques, the containment problem can be converted into cooperative output regulation problem. Moreover, they artfully construct regulation equations, whose solutions are also given. Adaptive protocols are proposed here by assigning a time‐varying coupling weight to each node. Unlike most existing protocols that depend on certain global information, protocols presented in this paper are independent of any global information, and hence are fully distributed. By combining the compensator technique with adaptive control, they propose the distributed dynamic adaptive state feedback and adaptive output feedback protocols for driving followers into the moving convex hull spanned by leaders. The obtained results are applied to the containment control of a network of heterogeneous agents, where the followers are described by mass‐damper spring systems, and the leaders are specified by harmonic oscillators. [ABSTRACT FROM AUTHOR]

This study considers the observer‐based consensus tracking problem of linear multi‐agent systems with input saturation. Existing observer‐based consensus protocols are designed based on an undirected graph, and need global information, such as the network size or eigenvalue information of the Laplacian matrix. In this study, based on only the agent dynamics and the relative outputs of neighbouring agents, an adaptive consensus protocol is proposed by assigning a time‐varying coupling weight to each node, and this protocol is independent of any global information and hence is fully distributed. Under the assumptions that each agent is asymptotically null controllable with bounded controls and detectable, and the topological graph has a directed spanning tree with the leader as the root node, semi‐global observer‐based consensus tracking of multi‐agent systems can be reached despite actuator saturation occurring. The results are applied to consensus tracking control of two‐mass‐spring systems, which are well‐known models for vibration in many mechanical systems. [ABSTRACT FROM AUTHOR]

In order to tackle the marine practical constraints, for example the actuator faults, the dead‐zone input, an improved composite adaptive neural control algorithm is proposed for dynamic positioning vehicles in presence of the unknown external disturbances. In the algorithm, the robust neural damping technique is employed to remodel the system model uncertainty and suppress the external interference. As for the dead‐zone input, the dead‐zone inverse model is constructed to derive the corresponding compensating terms. That could effectively release the constraints from the actuator faults and the dead‐zone non‐linearity. Furthermore, for merits of the composite intelligent learning method, one designs the serial‐parallel estimation model to estimate the related velocity variables. The corresponding prediction error could be applied in the design of adaptive law. That could effectively improve the accuracy of parameter estimation and facilitate the robustness of the closed‐loop system. The semi‐global uniformly ultimately bounded stability is guaranteed for all error signals in the closed‐loop system by utilizing the Lyapunov theory. Finally, the validity of the proposed algorithm is demonstrated through the simulation experiments. [ABSTRACT FROM AUTHOR]

This study considers the control problem for a class of non‐linear singularly perturbed systems (SPSs) subject to actuator saturation. A sufficient condition for the existence of state‐feedback controllers to achieve a prescribed stability bound is proposed and the corresponding basin of attraction is estimated. Then a convex optimisation problem is formulated, by which an optimal controller can be obtained to achieve a prescribed stability bound and simultaneously maximise the estimate of the basin of attraction of the SPSs for any allowable singular perturbation parameter. Furthermore, a stability condition is established, which improves the existing stability bound analysis methods for a class of non‐linear SPSs. Finally, examples are given to show the advantages and effectiveness of the obtained results. [ABSTRACT FROM AUTHOR]

Based on the improved radial basis function (RBF) neural networks, the distributed three‐dimension formation control scheme in the presence of dynamic uncertainties is studied for non‐linear multi‐agent systems with time delay. A virtual leader which tracks the desired signal is followed by all agents adaptively. Linear reduced‐order observers are designed on the basis of absolute and local state errors of each agent. The local state error and absolute state error are generated between neighbouring agents and each individual agent in formation, respectively. The time delay for each agent in the formation can be offset by designing a Lyapunov function, which can simplify the controller design. To deal with non‐linear dynamic uncertainties and unavoidable disturbance, improved RBF neural networks are employed. In comparison with traditional RBF neural networks, improved RBF neural networks can provide better convergence performance. Subsequently, the formation controller is designed and the stability of the systems is validated by using a new Lyapunov function. Numerical simulation is conducted to demonstrate the effectiveness of the proposed method for non‐linear multi‐agent time‐delay systems. [ABSTRACT FROM AUTHOR]

In this study, a new adaptive controller is introduced for the induction motors (IMs) based on immersion and invariance (I&I) technique. The dynamics of the IM system are perturbed by some disturbances such as time‐varying rotor resistance and load torque. Accordingly, an adaptive controller is designed and the uncertain parameters are online estimated. The adaptation laws are obtained from the stability analysis based on I&I method. The simulation results verified the effectiveness of the proposed control method. It is revealed that the outputs of the IM could track the desired signals in the presence of the mentioned disturbances. Also, the results are compared with the conventional control methods and it is concluded that the proposed control approach resulted in better performance. [ABSTRACT FROM AUTHOR]

This study deals with the protocol design for achieving robust global consensus tracking of multi‐agent systems. Agent dynamics are described as general linear systems with actuator saturation and input additive uncertainties and disturbances. Via developing a scheduled low‐and‐high gain design technique, the state feedback protocol is proposed, under which global consensus tracking and disturbance rejection for such systems can be achieved under the mild assumptions on agent dynamics and network topology. This result is further extended to the case of the reduced‐order observer‐based protocol design, with the help of the special coordinate basis approach. Finally, the advantages of the proposed protocols are illustrated by a numerical simulation. [ABSTRACT FROM AUTHOR]

In this note, a novel adaptive constrained control algorithm is proposed for dynamic positioning vessels in the presence of input amplitude and rate saturations. In the scheme, both kinematics and kinetics loops are augmented by the auxiliary system to deal with the saturation impact. Meanwhile, for merits of the command filters and minimal leering parameter technique, the cumbersome analytic derivatives of the virtual control law need not be required in the control design, and only two adaptive parameters are updated online to stabilise the effect of the model uncertainty and the external disturbance for each subsystem. Using the Lyapunov theory, the semi‐global uniformly ultimately bounded is proved for the closed‐loop system. The effectiveness and robustness of the proposed algorithm are demonstrated by the numerical example in the presence of the simulated marine disturbance. [ABSTRACT FROM AUTHOR]

A two‐degree‐of‐freedom consensus scheme is investigated for fractional‐order multi‐agent systems with time delay. The two‐degree‐of‐freedom protocol including the individual controllers and the coupling controllers can realise the global tasks and improve consensus performance. Based on such a protocol, a closed‐loop multi‐input multi‐output framework in frequency domain is established. Then the multi‐agent system is decoupled into several subsystems with respect to the eigenvalues of the Laplacian matrix. For each subsystem, the robust stabilising region of the individual controller satisfying H∞ index is obtained on the basis of the improved D‐partition method. The controller parameters chosen in the region can provide robustness for the individual agent. The parameters of the coupling controller that ensure fast consensus are determined by first deriving the stabilising region and then searching for the fastest consensus speed in the obtained region. The two‐degree‐of‐freedom structure can trade off the consensus performance and disturbance rejection and is applicable to arbitrary‐order multi‐agent systems with time delay including the fractional‐order system and the integer‐order system. The two‐degree‐of‐freedom consensus controller satisfying other performance criteria can also be designed based on the resultant stabilising region. The simulation results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This study addresses the distributed H∞ and H2 consensus control problems for multi‐agent systems with general integrator dynamics and undirected topology. First, based on the frequency domain description of linear multi‐agent systems, a sufficient and necessary condition is imposed on each controller to achieve consensus. Second, both H∞ and H2 optimal controllers are computed analytically according to the corresponding performance indices. The novel controllers not only can optimise the reference tracking performance but also has a simple tuning way to trade off the nominal performance and robustness. Finally, by application to the formation control of autonomous surface vessels shows the effectiveness of the proposed two control strategies. [ABSTRACT FROM AUTHOR]

This study addresses the networked control problem for event‐triggered systems with quantisation effect and actuator fault. A new type of finite‐level dynamic logarithmic quantiser is proposed here. Firstly, when the actuator is subjected to deterministic fault and time delay occurs in the network between the sensor and the controller, stability analysis and stabilisation of the system are accomplished. Secondly, suppose the actuator is subjected to stochastic fault and there is packet dropout in the network between the sensor and the controller, the asymptotic stability of the system is analysed, and a mean‐square feedback controller is designed. Finally, simulation studies are made to verify the effectiveness of the presented method. [ABSTRACT FROM AUTHOR]

This study presents a new observer‐based electronic line‐shafting (ELS) control scheme as motion synchronisation solution for motor drives in the industrial manufacturing process. To achieve better speed control performance for each ac motor drive, a sliding mode controller is proposed. This controller is designed based on a non‐linear reaching law, which helps to settle the reaching time/chattering dilemma in the conventional sliding mode control (SMC) approach. In addition, a sliding mode observer is proposed to estimate lumped disturbances for the motor drives. Disturbance estimation results are fed forward as compensation parts for the SMC controller; in the meantime, they are transmitted to the virtual line‐shafting drive to accurately reflect total system disturbances, thus to achieve high motor speed synchronisation precision. Effectiveness of the proposed ELS control scheme is verified by simulation results. [ABSTRACT FROM AUTHOR]