Halim Alwi

Brief paper: Fault tolerant control using sliding modes with on-line control allocation

This paper proposes an on-line sliding mode control allocation scheme for fault tolerant control. The effectiveness level of the actuators is used by the control allocation scheme to redistribute the control signals to the remaining actuators when a fault or failure occurs. The paper provides an analysis of the sliding mode control allocation scheme and determines the nonlinear gain required to maintain sliding. The on-line sliding mode control allocation scheme shows that faults and even certain total actuator failures can be handled directly without reconfiguring the controller. The simulation results show good performance when tested on different fault and failure scenarios.

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.

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.

Design and Analysis of an Integral Sliding Mode Fault-Tolerant Control Scheme

A novel scheme for fault-tolerant control is proposed in this paper, in which integral sliding mode ideas are incorporated with control allocation to cope with the total failure of certain actuators, under the assumption that redundancy is available in the system. The proposed scheme uses the effectiveness level of the actuators to redistribute the control signals to healthy actuators without reconfiguring the controller. The effectiveness of the proposed scheme against faults or failures is tested in simulation based on a large transport aircraft model.

Fault Tolerant Sliding Mode Control Design with Piloted Simulator Evaluation

This paper considers sliding mode allocation schemes for fault tolerant control. The schemes allow redistribution of the control signals to the remaining functioning actuators when a fault or failure occurs. The paper analyzes the schemes and determines conditions under which closed-loop stability is retained for a certain class of faults and failures. It is shown that faults and even certain total actuator failures can be handled directly without reconfiguring the controller. The results obtained from implementing the controllers on a research flight simulator, configured to represent a B747 aircraft, show good performance in both nominal and failure scenarios, even in wind and gust conditions.

Fault reconstruction using a LPV sliding mode observer for a class of LPV systems

Abstract This paper proposes a new sliding mode observer for fault reconstruction, applicable for a class of linear parameter varying (LPV) systems. Observer schemes for actuator and sensor fault reconstruction are presented. For the actuator fault reconstruction scheme, a virtual system comprising the system matrix and a fixed input distribution matrix is used for the design of the observer. The fixed input distribution matrix is instrumental in simplifying the synthesis procedure to create the observer gains to ensure a stable closed-loop reduced order sliding motion. The ‘output error injection signals’ from the observer are used as the basis for reconstructing the fault signals. For the sensor fault observer design, augmenting the LPV system with a filtered version of the faulty measurements allows the sensor fault reconstruction problem to be posed as an actuator fault reconstruction scenario. Simulation tests based on a high-fidelity nonlinear model of a transport aircraft have been used to demonstrate the proposed actuator and sensor FDI schemes. The simulation results show their efficacy.

A fault tolerant control allocation scheme with output integral sliding modes

In this paper a new fault tolerant control scheme is proposed, where only measured system outputs are assumed to be available. The scheme ensures closed-loop stability throughout the entire closed-loop response of the system even in the presence of certain actuator faults/failures. This is accomplished by incorporating ideas of integral sliding modes, unknown input observers and a fixed control allocation scheme. A rigorous closed-loop stability analysis is undertaken, and in fact a convex representation of the problem is created in order to synthesize the controller and observer gains. The efficacy of the proposed scheme is tested by applying it to a benchmark civil aircraft model.

Sliding Mode FTC With On-line Control Allocation

This paper proposes an on-line sliding mode control allocation scheme for fault tolerant control. The effectiveness level of the actuators is used by the control allocation scheme to redistribute the control signals to the remaining actuators when a fault or failure occurs. The paper provides an analysis of the sliding mode control allocation scheme and determines the nonlinear gain required to maintain sliding. The on-line sliding mode control allocation scheme shows that faults and even certain total actuator failures can be handled directly without reconfiguring the controller

Evaluation of a Sliding Mode Fault Tolerant Controller for the EL-AL Incident

This paper presents piloted flight simulator results associated with the EL-AL flight 1862 scenario using a model reference–based sliding mode control allocation scheme for fault tolerant control. The proposed controller design was carried out without any knowledge of the type of failure, and in the absence of any fault detection and isolation strategy. This is motivated by the fact that the flight crew were unaware of the loss of the right engines. For this reason, the control allocation scheme which is proposed uses (fixed) equal distribution of the control signals to all actuators (for both nominal situations and when a fault or failure occurs). The paper analyzes the scheme and determines the conditions under which closed-loop stability is retained. The results represent the successful real-time implementation of the proposed controller on the SIMONA motion flight simulator configured to represent a B747 aircraft. The evaluation results from the experienced pilots show that the proposed controller has the ability to position the aircraft for landing in both a nominal and the EL-AL failure scenario. It is also shown that actuator faults and failures which occured during the EL-AL incident can be handled directly without reconfiguring the controller.

Robust sensor fault estimation for tolerant control of a civil aircraft using sliding modes

This paper proposes a sensor fault tolerant control scheme for a large civil aircraft. It is based on the application of a robust method for sensor fault reconstruction using sliding mode theory. The novelty lies in the application of the sensor fault reconstruction scheme to correct the corrupted measured signals before they are used by the controller and therefore the controller does not need to be reconfigured to adapt to sensor faults