Fault-Tolerant Control

Fault Tolerance Passive Passive  Tolerance achieved by the use of feedback control laws that are robust to possible system faults. Active Active  Tolerance achieved through a fault diagnosis and accommodation architecture.

Overview Detection Isolation Identification Accommodation Detection Isolation Identification Accommodation  Detection – Indicates the occurrence of a fault.  Isolation – Determines the type and/or location of the fault.  Identification – Determines the magnitude of the fault.  Accommodation – Fault is self-corrected, usually through controller reconfiguration. Diagnosis

A Fault-Tolerant Control Architecture

Fault Accommodation Nominal Controller Nominal Controller Guarantees the stability and tracking performance. Guarantees the stability and tracking performance. Maintains the system signal boundedness until the fault is detected. Maintains the system signal boundedness until the fault is detected. Fault-Tolerant Controller (I) Fault-Tolerant Controller (I) Used right after fault detection. Used right after fault detection. Fault-Tolerant Controller (II) Fault-Tolerant Controller (II) Used after fault isolation. Used after fault isolation. Purpose – Improve/recover performance. Purpose – Improve/recover performance.

General (Nonlinear) Plant Represents the deviation in the system dynamics due to the occurrence of a fault.

Fault time profile Unknown fault evolution rate Small – slowly developing faults. Large – abrupt faults (step function). Only reflects the speed of the fault.

Faults

Modes of Behavior

General Controller

A More Detailed Architecture

Specific Plant Structure

Design of The Nominal Controller

The Nominal Controller The control laws for the First Controller Reconfiguration and Second Controller Reconfiguration take on similar forms.

Different Approaches of Fault Isolation This paper dealt with determining the type of the fault among a set of known possible fault types. This paper dealt with determining the type of the fault among a set of known possible fault types. Other approaches: Other approaches:  For physically distributed systems, determining the physical location of the fault.  For complex systems, determining the faulty subsystem among the set of all subsystems.

Multiple Faults This paper assumed only a single fault could occur at any time. This paper assumed only a single fault could occur at any time. In some applications, multiple faults may occur simultaneously or sequentially In some applications, multiple faults may occur simultaneously or sequentially  In this case, a diagonal fault sensitivity structure is required.