This paper deals with the issues of sensor fault estimation, actuator fault detection and isolation for a class of uncertain nonlinear systems. By taking the sensor fault vector as a part of an extended state vector, the original system with sensor faults, actuator faults and unknown inputs is transformed into an augmented singular system which is just with actuator faults and unknown inputs. For the constructed singular system, a robust sliding-mode observer is developed to simultaneously estimate the states and sensor faults of original system, and the observer gain matrices are computed in terms of linear matrix inequalities by solving an optimization problem. Then an actuator fault detector is designed to detect actuator faults when ones occur, and multiple observers used as actuator fault isolators are proposed to identify which actuator is with fault. Finally, a simulation example is given to illustrate the effectiveness of the proposed methods.

In this article, a leader–follower asymptotic consensus control strategy is developed for a class of linear multiagent systems (MASs) with unknown external disturbances and measurement noises. First, the preconditions, the minimum phase condition (MPC) and observer matching condition (OMC), are discussed in detail, and an equivalent result under these two preconditions is given. In this way, the corresponding results from Corless and Tu (1998) are improved. Meanwhile, a reduced-order observer is designed for a constructed augmented system to estimate the system states and noises of each agent. Next, with the help of a traditional interval observer, a novel unknown disturbance reconstruction method is developed, and the reconstruction can converge to the unknown disturbance asymptotically and decouple from the control input. The subsequent asymptotic consensus is accomplished by utilizing an observer-based control scheme, with its design satisfying the so-called separation principle. Finally, two simulation examples are given to verify the effectiveness and show the advantages of the proposed methods.

This paper is concerned with the problem of observerbased sliding mode control designs for a class of descriptor T-S fuzzy systems with time-delay and uncertainties. Specifically, based on the detailed discussions on the existence conditions, a reducedorder robust observer is designed firstly where the influences of the uncertainties are totally removed. Secondly, by choosing appropriate coordinate transformations and matrix decompositions, an actual and a virtual sliding mode variables are constructed, and an observer-based sliding mode controller is developed to handle the uncertainties such that the virtual sliding mode surface can be reached and maintained in a finite time, while the actual sliding mode variable approaches to zeros asymptotically. And then, we prove that the system asymptotic stability can be guaranteed after the virtual sliding mode surface has been reached or the actual sliding mode variable approached to zero. In addition, the existence conditions for both the observer and the sliding mode controller are given in strict linear matrix inequility forms. Finally, a simulation example is given to demonstrate the effectiveness of the proposed method.

This paper is concerned with the design of the distributed prescribed-time unknown input observer (DPTUIO) for a class of linear time-invariant (LTI) systems, which we refer to as the target systems. Results on distributed unknown input observers in the literature did not address the convergence time predefinition problem. To achieve fast estimation, this paper uses weakly unobservable subspace decomposition and introduces a time-scale transformation technology to develop a novel DPTUIO. This design ensures that, for each node, the entire state of the target system can be estimated within a pre-assigned time, despite each node measuring only a small portion of the system output. Detailed discussions on the existence conditions of the DPTUIO are provided. It is established that the observer matching condition, along with the jointly strongly observability condition and a strongly connected communication network, constitutes sufficient conditions for the existence of the DPTUIO. Moreover, the robustness of the developed DPTUIO against measurement and communication noise is analyzed in detail with rigorous deduction. Finally, a practical example is used to verify the effectiveness of the proposed methods.

This article addresses the issues of the bipartite time-varying formation (BTVF) control for multiagent systems (MASs) on signed digraphs. All the designs are performed under the assumptions that the leader and followers suffer from external disturbances, the control input signal of the leader is unreachable to any follower, and the state variables of the followers are unmeasurable. To begin with, an unknown input observer (UIO) is designed for each follower using a traditional interval observer to obtain the state estimates. To realize the BTVF tracking, a distributed consensus error dynamic system is constructed. Furthermore, a distributed unknown input reconstruction method is developed to estimate the multiple disturbances in the consensus error system. Then, an event-triggered BTVF control protocol is proposed which allows two antagonistic time-varying formations to be formed, while excluding Zeno behavior. A simulation of a group of wheeled robots is used to demonstrate the performance of the proposed methods.