Afef Fekih

Adaptive PID-Sliding-Mode Fault-Tolerant Control Approach for Vehicle Suspension Systems Subject to Actuator Faults

Advanced fault-tolerant control schemes are required for ensuring efficient and reliable operation of complex technological systems such as ground vehicles. A novel approach to fault-tolerant control design is proposed for a full-scale vehicle dynamic model with an active suspension system in the presence of uncertainties and actuator faults. The proposed control scheme uses a sliding-mode controller to generate the tracking signal to the valve for each of the four wheel subsystems for mitigating three degrees of freedom (3-DOF) heave-roll-pitch motion arising from road undulations. For each of the electrohydraulic valve-cylinder pair in each subsystem, an adaptive proportional-integralderivative (PID) controller is proposed. Designing an adaptation scheme for the PID gains to accommodate actuator faults is among the main contributions of this work. The focus on actuator faults is motivated by the fact that loss of actuator effectiveness is a critical fault scenario in vehicle suspension systems and that the probability of occurrence of faults in actuators is higher and more severe when compared with other components. To analyze the performance of the proposed approach, computer simulations are carried out to illustrate control performance, robustness, and fault tolerance. The performance of our approach is then compared with that of the sliding-mode control (SMC) approach presented by Chamseddine and Noura. Results clearly indicate the strength of the adaptation scheme and its ability to mitigate fault effects in a short time. Simplicity of the overall scheme and the stabilization of the system under both faulty and fault-free conditions are the main positive features of the proposed approach.

Fault-tolerant flight control design for effective and reliable aircraft systems

Effectiveness in flight control is achieved by maintaining specified performance despite the presence of faults and reliability implies taking the necessary measures to correct the fault before it leads to substantial performance deterioration and instability. In order to achieve both effectiveness and reliability, in this paper, we propose a fault-tolerant control (FTC) approach that is able to simultaneously compensate for actuator faults, model mismatch and parameter variations in aircraft systems. The proposed control design successfully combines the properties of active and passive FTCs to accommodate faults while retaining acceptable system performance. A passive baseline controller is designed using sliding mode theory and an active controller is designed using a model reference adaptive approach. The proposed control paradigm retains system performance under fault free conditions and triggers corrective measures only when necessary, hence ensuring flight effectiveness and enhancing system’s reliab...

Fault diagnosis and Fault Tolerant Control design for aerospace systems: A bibliographical review

This paper gives an overview of recent progress in theory and methods to analyze and design fault diagnosis and fault tolerant control techniques for aerospace systems. Passive and active approaches are presented and analyzed. Strongpoint and shortcomings of each approach are pointed out. Open problems related to the topic are also highlighted. The paper is written in a tutorial fashion to summarize some of the recent results in the subject area without going into details. A bibliographical review summarizing a decade of references is provided to allow interested readers to obtain more detailed information about the recent contributions in the field. Since the general areas of Fault Tolerant Control (FTC) and Fault Detection and Isolation (FDI) draws from a number of different technical areas in engineering and applied mathematics, no survey paper could hope to capture all existing contributions in the field.

Fault-Tolerant Control of Wind Turbine Systems - A Review

Wind turbine systems are complex and remotely-installed structures which are subject to many possible faults in the existed components. Early fault detection, isolation and successful controller reconfiguration can considerably increase the performance in faulty conditions and prevent abysmal failures in the system. This paper gives an overview of recent progress in theory and methods to analyze and design fault-tolerant control systems for wind turbines. A comparison between model-based and signal based fault detection methods is presented and the contributions in these areas are addressed. The paper is written in a tutorial fashion to summarize some of the recent results in the subject area without going into details. A bibliographical review summarizing the most recent publications is provided to allow interested readers to obtain more detailed information about the recent contributions in Fault Tolerant Control (FTC) and Fault Detection (FD) design for wind turbines.

A Stability Guaranteed Robust Fault Tolerant Control Design for Vehicle Suspension Systems Subject to Actuator Faults and Disturbances

A fault tolerant control approach based on a novel sliding mode method is proposed in this brief for a full vehicle suspension system. The proposed approach aims at retaining system stability in the presence of model uncertainties, actuator faults, parameter variations, and neglected nonlinear effects. The design is based on a realistic model that includes road uncertainties, disturbances, and faults. The design begins by dividing the system into two subsystems: a first subsystem with 3 degrees-of-freedom (DoF) representing the chassis and a second subsystem with 4 DoF representing the wheels, electrohydraulic actuators, and effect of road disturbances and actuator faults. Based on the analysis of the system performance, the first subsystem is considered as the internal dynamic of the whole system for control design purposes. The proposed algorithm is implemented in two stages to provide a stability guaranteed approach. A robust optimal sliding mode controller is designed first for the uncertain internal dynamics of the system to mitigate the effect of road disturbances. Then, a robust sliding mode controller is proposed to handle actuator faults and ensure overall stability of the whole system. The proposed approach has been tested on a 7-DoF full car model subject to uncertainties and actuator faults. The results are compared with the ones obtained using H∞ approach. The proposed approach optimizes riding comfort and road holding ability even in the presence of actuator faults and parameter variations.

A Passive Fault Tolerant Control Strategy for the uncertain MIMO Aircraft Model F-18

In this paper, we design a passive fault tolerant control strategy for an uncertain MIMO aircraft model F-18. A novel variable structure controller with sliding surface and Lyapunov function is proposed in order to eliminate the effect of certain type of pre-specified faults. The main features of the proposed control strategy are its simplicity and robustness against uncertainties and parameter variations and some pre-specified faults. Computer experiments illustrating the application of the proposed approach to the longitudinal flight control of an F-18 aircraft model are presented to show the effectiveness of the design method.

A multi-gain sliding mode based controller for the pitch angle control of a civil aircraft

A multi-gain sliding mode based controller for the pitch angle control of a civil aircraft is presented in this paper. The proposed controller is based on a novel concept of the sliding mode controllers in which multiple gains are being used to control the pitch angle of an aircraft and make it insensitive to parameter variations while reducing the chattering and guaranteeing the stability of the closed loop system. The proposed approach was implemented on a Delilah aircraft model to control the pitch angle under faulty conditions. Performance comparison between the traditional one gain SMC and the proposed multi-gains SMC are discussed.

A robust fault tolerant control strategy for aircraft systems

An integrated design that combines sliding mode control with adaptive control to provide a robust fault tolerant flight controller that works for a wide range of faults is proposed in this paper. The scheme combines the insensitivity and robustness properties of sliding mode control to certain types of disturbances and uncertainties with the accommodation properties of adaptive control to parametric and structural uncertainties caused by component faults and external disturbances. It is shown that parameter variations and actuator faults can be handled directly and system stability and performance is preserved under faulty conditions. The results obtained from implementing the controller to an F-16 aircraft system show good performance under both un-faulty and faulty scenarios.

A Fault Tolerant Control Design for Induction Motors

This paper describes a fault tolerant controller for high performance induction motor drive. The proposed approach aims to make the motor tolerant to both internal and external factors such as loading, temperature and sensor failure. To achieve this goal, a controller that switches itself between a control strategy designed for nominal operation and a robust control strategy designed for faulty conditions is developed. The switching function serves as the fault indicator as well. To compensate for sensor faults, a practical speed estimator and an open loop flux observer with online tuning of rotor resistance are proposed. Simulation experiments in terms of speed and flux responses show the effectiveness of the proposed approach

A Nonlinear State Feedback Controller for Induction Motors

In this article, a novel approach to nonlinear control of induction motors is presented. The proposed approach is used to design controllers for the rotor flux amplitude and the motor speed. The underlying design objective is to endow the closed loop system with high performance dynamics for high speed ranges while keeping the required stator voltage within the inverter ceiling limits. A comparative study between the performances of the proposed controller and field oriented control is carried out. The methods are compared in terms of their ability to handle loads on the motor shaft, their speed tracking capability and their sensitivity to operating condition variations. To estimate the rotor flux, an open loop observer is developed.