Roozbeh Izadi-Zamanabadi

Fault-tolerant control systems — A holistic view

Abstract Fault-tolerant control is used in systems that need to be able to detect faults and prevent simple faults related to control loops from developing into production stoppages or failures at a plant level. This is obtained by combining fault detection with supervisory control and re-configuration to accommodate faults. Much attention has been focused on fault detection in its own right. This paper deals with fault tolerant control from a much wider point of view, covering the entire design process from the engineering of the interface to structural implementation. Experience ranging from a simple temperature control to a complex satellite control system demonstrates significant improvements in plant availability using simple means.

Model based fault detection in a centrifugal pump application

A model based approach for fault detection in a centrifugal pump, driven by an induction motor, is proposed in this paper. The fault detection algorithm is derived using a combination of structural analysis, observer design and Analytical Redundancy Relation (ARR) design. Structural considerations on the system is used to divide it into two cascaded connected subsystems, giving an example on using a general structural approach to divide a complex problem into a set of less complex and solvable problems. The variables connecting the two subsystems are observed using an adaptive observer derived on the basis of the equations describing the first subsystem. No faults are expected to affect the first subsystem, therefore only the second subsystem is considered in the design of the fault detection algorithm. The fault detection algorithm is based on an ARR, which is designed using structural analysis and the Groebner basis algorithm. The polynomial form of the obtained ARR is utilized to achieve robustness w.r.t. parameter variations by using a set-valued approach. The applicability of the algorithm is illustrated by applying it to an industrial benchmark. The benchmark tests have shown that the algorithm is capable of detecting four different faults in the mechanical and hydraulic parts of the pump.

Proceedings of the 13th Mediterranean Conference on Control and Automation

An equivalent circuit method describing the free stator of piezoelectric motor is presented in this paper, while the circuit elements have complex values. The mechanical, dielectric and piezoelectric losses associated with the vibrator are accounted for by the imaginary components of the circuit elements. It is shown that the calculation of the circuit parameters from the complex elastic, dielectric and piezoelectric material constants is straightforward and the model accuracy is verified with simulation around the important frequencies suitable for motor controller design purposes

Observer-Based Estimation of Stator-Winding Faults in Delta-Connected Induction Motors: A Linear Matrix Inequality Approach

This paper addresses the subject of interturn short circuit estimation in the stator of a delta-connected induction motor. In this paper, an adaptive observer scheme is proposed. The proposed observer is capable of simultaneously estimating the speed of the motor, the amount turns involved in the short circuit, and an expression of the current in the short circuit. Moreover, the states of the motor are estimated, meaning that the magnetizing currents are made available even though a fault has occurred in the motor. To be able to develop this observer, a model that is particularly suitable for the chosen observer design, is also derived. The efficiency of the proposed observer is demonstrated by tests performed on a test setup with a customized designed induction motor. With this motor it is possible to simulate interturn short-circuit faults.

Structural analysis approach to fault diagnosis with application to fixed-wing aircraft motion

The paper presents a structural analysis based method for fault diagnosis purposes. The method uses the structural model of the system and utilizes the matching idea to extract systems inherent redundant information. The structural model is represented by a bipartite directed graph. FDI possibilities are examined by further analysis of the obtained information. The method is illustrated by applying on the LTI model of motion of a fixed-wing aircraft.

A structural analysis method formulation for fault-tolerant control system design

An analysis of structural model representation has been used to extract available inherent redundant information in the system. The paper presents a refined structural model representation based on bipartite directed graph definition and the necessary condition for structural observability are proposed.

Estimation of stator winding faults in induction motors using an adaptive observer scheme

This paper addresses the subject of inter-turn short circuit estimation in the stator of an induction motor. In the paper an adaptive observer scheme is proposed. The proposed observer is capable of simultaneously estimating the speed of the motor, the amount turns involved in the short circuit and an expression of the current in the short circuit. Moreover the states of the motor are estimated, meaning that the magnetizing currents are made available even though a fault has happened in the motor. To be able to develop this observer, a model particular suitable for the chosen observer design, is also derived. The efficiency of the proposed observer is demonstrated by tests performed on a test setup with a customized designed induction motor. With this motor it is possible to simulate inter-turn short circuit faults.

Passive fault-tolerant control of discrete time piecewise affine systems against actuator faults

In this article, we propose a new method for passive fault-tolerant control of discrete time piecewise affine systems. Actuator faults are considered. A reliable piecewise linear quadratic regulator state feedback is designed such that it can tolerate actuator faults. A sufficient condition for the existence of a passive fault-tolerant controller is derived and formulated as the feasibility of a set of linear matrix inequalities (LMIs). The upper bound on the performance cost can be minimised using a convex optimisation problem with LMI constraints which can be solved efficiently. The approach is illustrated on a numerical example and a two degree of freedom helicopter.

Reliable Control of Ship-Mounted Satellite Tracking Antenna

Motorized antenna is a key element in overseas satellite telecommunication. The control system directs the on-board antenna toward a chosen satellite while the high sea waves disturb the antenna. Certain faults (communication system malfunction or signal blocking) cause interruption in the communication connection resulting in loss of the tracking functionality, and instability of the antenna. In this brief, a fault tolerant control (FTC) system is proposed for the satellite tracking antenna. The FTC system maintains the tracking functionality by employing proper control strategy. A robust fault diagnosis system is designed to supervise the FTC system. The employed fault diagnosis solution is able to estimate the faults for a class of nonlinear systems acting under external disturbances. Effectiveness of the method is verified through implementation and test on an antenna system.

Towards Automatic Model Based Controller Design for Reconfigurable Plants

This paper introduces model-based Plug and Play Process Control, a novel concept for process control, which allows a model-based control system to be reconfigured when a sensor or an actuator is plugged into a controlled process. The work reported in this paper focuses on composing a monolithic model from models of a process to be controlled and the actuators and sensors connected to the process, and propagation of tuning criteria from these sub-models, thereby accommodating automatic controller synthesis using existing methods. The developed method is successfully tested on an industrial case study from Danfoss A/S, where the process to be controlled is the indoor temperature of a house and the actuators acting on the process are a floor heating system and an electric radiator.