Chee Pin Tan

Fault detection and fault-tolerant control using sliding modes

Introduction.- Fault Detection and Isolation and Fault-tolerant Control.- First-order Sliding-mode Concepts.- Sliding-mode Observers for Fault Detection.- Cascaded Sliding-mode Observers.- Sensor Fault Detection.- Adaptive Sliding-mode Fault-tolerant Control.- Fault-tolerant Control using Sliding Modes with On-line Control Allocation. Model-reference Sliding-mode FTC.- SIMONA Implementation Results.- Case Study I: GARTEUR AG16, El Al Flight 1862 Bijlmermeer Incident.- Case Study II: Propulsion-controlled Aircraft.

An LMI approach for designing sliding mode observers

This paper presents a method to design sliding mode observers for a class of uncertain systems using linear matrix inequalities. The objective is to exploit the degrees of freedom available in the design which have hitherto been ignored because of the lack of a tractable solution framework. The relationship between the linear component of the sliding mode observer and a particular sub-optimal observer arising from classical linear quadratic Gaussian (LQG) theory is demonstrated. This helps motivate how the design weighting matrices inherent in the method may be chosen in practice. It will also be shown how the weighting matrices affect the dynamics of the sliding motion. Furthermore, using pole-placement and pole clustering methods, the poles of the sliding motion can be forced to lie in a specified region in the complex plane, so that the performance of the sliding motion can be tuned. This paper will also present a more general solution where the eigenvalues of the linear part of the observer are forced to lie in a specified region.

Brief paper: Sliding mode estimation schemes for incipient sensor faults

This paper proposes a new method for the analysis and design of sliding mode observers for sensor fault reconstruction. The proposed scheme addresses one of the restrictions inherent in other sliding mode estimation approaches for sensor faults in the literature (which effectively require the open-loop system to be stable). For open-loop unstable systems, examples can be found, for certain combinations of sensor faults, for which existing sliding mode and unknown input linear observer schemes cannot be employed, to reconstruct faults. The method proposed in this paper overcomes these limitations. Simulation results demonstrate the effectiveness of the design framework proposed in the paper.

Technical communique: Terminal sliding mode observers for a class of nonlinear systems

This paper proposes a terminal sliding mode observer for a class of nonlinear systems to achieve finite time convergence for all error states. Compared to standard sliding mode observers which only enable finite time convergence of the output error, the observer in this paper makes use of fractional powers to reduce other non-output errors to zero in finite time. A 2-degree-of-freedom robotic manipulator is used to demonstrate the effectiveness of the proposed observer.

Robust Fault Reconstruction in Uncertain Linear Systems Using Multiple Sliding Mode Observers in Cascade

In observer-based fault reconstruction, one of the necessary conditions is that the first Markov parameter from the fault to the output must be full rank. This paper seeks to relax that requirement by using multiple sliding mode observers in cascade. Signals from an observer are used as the output of a fictitious system whose input is the fault. Another observer is then designed and implemented for the fictitious system. This process is repeated until the first Markov parameter of the fictitious system with respect to the fault is full rank. The result is that robust fault reconstruction can be carried out for a wider class of systems compared to other works that also seek to relax the requirement of a full rank first Markov parameter. In addition, this paper has also investigated and presented the necessary and sufficient conditions as easily testable conditions, and also the precise number of observers required. A simulation example verifies the effectiveness of the scheme.

Brief paper: Extended results on robust state estimation and fault detection

A common requirement implicit in the current methods for the design of robust state estimators and robust fault detection filters is that the first Markov matrix must be non-zero, and indeed, full rank. We relax both of these restrictions in this paper to allow the applicability to a wider range of systems. The extended results are then applied to an aircraft fault detection for which the restrictive condition is not satisfied.

Fault tolerant control using sliding mode observers

Previous work has considered the use of sliding mode observers for fault detection and isolation (FDI) in uncertain linear systems whereby the unknown faults are reconstructed by appropriate processing of the so-called equivalent output error injection. The paper builds on this work and considers such a scheme within the broader context of fault tolerant control. Specifically, by correcting the faulty measurement by an estimate of the fault obtained from the sliding mode FDI scheme, good closed-loop performance is still maintained. An example of such a scheme, which has been implemented on a laboratory dc motor rig, is described.

Sliding mode methods for fault detection and fault tolerant control with application to aerospace systems

Sliding mode methods for fault detection and fault tolerant control with application to aerospace systems Sliding mode methods have been historically studied because of their strong robustness properties with regard to a certain class of uncertainty, achieved by employing nonlinear control/injection signals to force the system trajectories to attain in finite time a motion along a surface in the state-space. This paper will consider how these ideas can be exploited for fault detection (specifically fault signal estimation) and subsequently fault tolerant control. It will also describe applications of these ideas to aerospace systems, including piloted flight simulator results associated with the GARTEUR AG16 Action Group on Fault Tolerant Control. The results demonstrate a successful real-time implementation of the proposed fault tolerant control scheme on a motion flight simulator configured to represent the post-failure EL-AL aircraft.

Sliding mode methods for fault detection and fault tolerant control

Sliding mode methods have been historically studied because of their strong robustness properties to a certain class of uncertainty. This is achieved by employing nonlinear control/injection signals to force the system trajectories to attain in finite time a motion along a surface in the state-space. This paper will consider how these ideas can be exploited for fault detection (specifically fault signal estimation) and subsequently fault tolerant control. The paper will also describe applications of these ideas to aerospace systems. It will describe piloted flight simulator results associated with the GARTEUR AG16 action group on fault tolerant control. The results demonstrate the successful real-time implementation of the proposed fault tolerant control scheme on a motion flight simulator configured to represent the EL-AL aircraft.

Sliding-Mode Observers

The focus of much of the research in the area of control systems theory during the seventies and eighties addressed the issue of robustness - i.e., designing controllers with the ability to maintain stability and performance in the presence of discrepancies between the plant and model. One nonlinear approach to robust controller design which emerged during this period is the Variable Structure Control Systems methodology. Variable Structure Control Systems evolved from the pioneering work in Russia of Emel’yanov and Barbashin in the early 1960’s. The ideas did not appear outside the Soviet Union until the mid 1970’s when a book by Itkis [20] and a survey paper by Utkin [29] were published in English. Variable structure systems concepts have subsequently been utilized in the design of robust regulators, model-reference systems, adaptive schemes, tracking systems and state observers. The ideas have successfully been applied to problems as diverse as automatic flight control, control of electrical motors, chemical processes, helicopter stability augmentation, space systems and robotics [12, 23, 28, 30].