Nonlinear Observer-based Approach Research Articles

A passive isolation of sensor faults from un-stealthy attacks in uncertain nonlinear systems

In this paper, a novel nonlinear observer-based approach is established to cast light on the problem of isolating sensor faults from un-stealthy attacks for Lipschitz affine nonlinear systems subjected to unknown uncertainties and disturbances. A structure consisting of a multi-line transmission mechanism, a random number generator (RNG), and Dedicated Observer Scheme is developed to make the abnormal behaviors distinguishable. A group of two interlinked nonlinear Luenberger-Like observers is designed in nonlinear coordinates to detect abnormal behaviors. Two banks of detection observers and an incidence matrix are introduced to make the final decisions. Adaptive threshold techniques are exploited to guarantee the robustness against the model uncertainties and disturbances. Compared with the existing results, the proposed approach isolates the abnormal behaviors without the need for any redundant hardware components. Finally, the performance of the proposed approach is evaluated on a continuous stirred tank reactor (CSTR).

A Nonlinear Observer-Based Approach to Robust Cooperative Tracking for Heterogeneous Spacecraft Attitude Control and Formation Applications

This article proposes a nonlinear observer-based approach to address the robust cooperative tracking problem and application for heterogeneous spacecraft systems. By introducing appropriate assumptions, a weight average estimation is proposed to construct a class of distributed nonlinear observers for heterogeneous spacecraft systems with a target whose dynamics are available only to a few chasers. By synthesizing the observer dynamics among the neighbors, a novel cooperative tracking controller is developed to address nonidentical parameters both in model uncertainties and nonlinear dynamics. Then, the robust consensus tracking problem can be solved if the cooperative behaviors between the chasers and their observers can be achieved synchronically. A special case of the identical model uncertainty and nonlinear dynamics scenario is also discussed. As applications of the proposed nonlinear observer-based approaches, the controller and observer designs of heterogeneous spacecraft attitude control and formation flying systems are revisited. Numerical simulations with a nonlinear dynamic model of spacecraft attitude control and formation flying systems demonstrate the effectiveness of the proposed approaches.

Nonlinear observer-based approach for cooperative control of networked rigid spacecraft systems

This paper considers the cooperative control problem for a multi-agent agent system composed of rigid spacecraft systems with quaternion-based attitude representation and a dynamic leader system, whose angular velocity is generated from a general nonlinear system. A distributed nonlinear observer is first proposed to estimate the input of the nonlinear leader system, based on which, a nonlinear internal-model-based observer is constructed, capable of estimating nonlinear signals with parametric uncertainty. Then observer-based local controllers are designed to achieve the asymptotic tracking of the leader’s attitude and angular velocity, the latter of which is also robust to the uncertain mass property of the rigid spacecraft systems.

A nonlinear observer-based approach to fault detection, isolation and estimation for satellite formation flight application

In this paper, the problem of fault diagnosis for a satellite formation flight is considered. A scheme is investigated for fault detection, isolation, and estimation of a class of nonlinear systems. In this scheme, we consider the model uncertainty, input and environmental disturbances. For fault detection, a nonlinear observer is designed to minimize the uncertainty within ℋ∞ framework. The Linear Matrix Inequality (LMI) formulation is used to obtain the observer gain matrices. In the next step, a bank of nonlinear robust unknown input observers is designed to isolate the faulty actuator. Fault isolation is achieved based on the generalized observer strategy. The proposed observer can simultaneously estimate faults and states; it can also decouple the unknown input disturbances and attenuate the effect of model uncertainty and external disturbances. In order to fulfill these goals, a Lipschitz formulation and Linear Parameter Varying (LPV) method are used in all of the proposed observers, which lead to less conservative LMI condition. Then, the mentioned approach is applied to fault diagnosis of a formation of satellites. Moreover, a distributed fault detection, isolation, and estimation scheme based on above observers is proposed. In this scheme, each satellite not only can diagnose its own faults but also it is able to diagnose its neighbors faults.

A robust nonlinear observer-based approach for distributed fault detection of input–output interconnected systems

This paper develops a nonlinear observer-based approach for distributed fault detection of a class of interconnected input–output nonlinear systems, which is robust to modeling uncertainty and measurement noise. First, a nonlinear observer design is used to generate the residual signals required for fault detection. Then, a distributed fault detection scheme and the corresponding adaptive thresholds are designed based on the observer characteristics and, at the same time, filtering is used in order to attenuate the effect of measurement noise, which facilitates less conservative thresholds and enhanced robustness. Finally, a fault detectability condition characterizing quantitatively the class of detectable faults is derived.

Intelligent Decentralized Adaptive Controller Design for a Class of Large Scale Nonlinear Non-affine Systems: Nonlinear Observer-based Approach

In this study, an observer based decentralized Fuzzy Adaptive Controller (FAC) is designed for a class of large scale non-affine nonlinear systems with unknown functions of the subsystems and interactions. The proposed controller has the following main characteristics: 1) On-line adaptation of both controller and observer parameters, 2) stabilization of the closed loop system, 3) convergence of both tracking and observer errors to zero, 4) boundedness of all signals involved, 5) being prone to employing experts' knowledge in controller design procedure, 6) chattering avoidance. An illustrative example is given to show the promising performance of the proposed method.

Nonlinear Control and Disturbance Compensation for Underactuated Ships Using Extended Linearisation Techniques

Both in maritime and inland water transport, sophisticated nonlinear control is of increasing importance to contribute to a growth in transport capacity while maintaining safety and reliability. In this paper, two alternative nonlinear control approaches are presented that are based on the technique of extended linearisation and lead to gain-scheduled feedback controllers: whereas in the first approach a fixed assignment of the closed-loop eigenvalues is made, the second approach follows the idea of linear-quadratic control (LQR), which results in a varying eigenvalue configuration in the complex plane. The feedback control part is extended by appropriate feedforward control to reduce the tracking error further. To achieve accurate trajectory tracking control tasks despite external disturbances by cross currents or wind forces in lateral direction a nonlinear observer-based approach to disturbance compensation is proposed in this paper. As a consequence of the use of extended linearisation techniques, the model-based design of the whole control structure avoids time-consuming heuristic parametrizations of gain-scheduled controllers. The efficiency and the achieved tracking performance are shown by simulation results. Here, both tracking behaviour and rejection of disturbance forces in lateral direction are considered.

Filtering for a class of nonlinear MIMO uncertain time-delay stochastic systems

In this article, a high-gain nonlinear observer-based approach is proposed for filtering of nonlinear stochastic systems with time delays. The system under consideration contains parameter uncertainties, stochastic disturbances, time delays, as well as Lipschitz-like nonlinearities. The objective is to design a robust filter such that the dynamics of the estimation error is guaranteed to be stochastically exponentially ultimately bounded in a sense of mean square. A new high-gain filter idea is introduced to solve the stochastic filtering problem by using the Lyapunov method and stochastic analysis techniques. The design of the proposed filter does not necessitate the resolution of any dynamics systems and its expression is explicitly given, i.e. its calibration is achieved through the choice of a single parameter, and does not rely on solving any matrix inequalities by numerical computation. A simulation example is given to illustrate the performance of the proposed filter.

Nonlinear Observer-Based OFC Detection for A380 Aircraft

In this paper, we address the problem of Oscillatory failure Case (OFC) detection in A380 aircraft. The importance of OFC detection is well known in the literature because of natural mode excitation and the structural loads they can provoke. A novel nonlinear observer-based approach, which has two different gains is proposed in this paper to solve the problem. The main advantage of the proposed residual generator is that, by an adequate selection of observer gains, the residual generator has a kind selective (frequency dependent) attenuation property: disturbances and unmodelled dynamics effects on the residual are reduced while the effect of the fault is slightly amplified in a specific fault frequency range. Further, if the gains are chosen to be zero, the particular case of the technique implemented on A380 Airbus is obtained. A test based on real measurements of an A380 airplane is presented to show the efficiency of the proposed residual over the existing techniques.

Observer-Based Strategies for Fault Diagnosis in a Three-Tank System

This paper investigates a non-linear observer-based approach to fault detection and isolation of the benchmark of a three-tank system. Observability of the benchmark system in several circumstances is studied. Non-linear observers are proposed. Strategies for fault detection and isolation in the benchmark using nonlinear observers are discussed.