Fault-tolerant Control

1
Fault-tolerant Control

• Motivation
• Definitions
• A general overview on the research area.
• Active Fault Tolerant Control (FTC)
• FTC- Analysis and Development procedure
• Supervisor architecture
• Logic realization
• Design and development tools
• Implementation

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Fault Tolerant Control

• Motivation
• Demand for higher autonomy and reliability
  requires considering all possible situations to
  guarantee correct and consistent operation
• Purpose
• Using a logically sound stepwise guideline to
  achieve
• Complete coverage of possible single faults.
• Supportive software tools.
• Avoiding unnecessary plant modelling.
• Automatic code generation.
• Initial Prerequisites
• Initial system concept is established.
• Systems requirements are specified (operating
  modes and functions, required performance,
  environmental, safety, or regularity requirements)

3
Approaches to achieve FTC
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FTC development procedure - I
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FTC Development procedure - II
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Fault Modelling
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Failure Mode and Effect Analysis -FMEA
FMEA scheme for the Wheel system
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FMEA Other examples
FMEA scheme for the GPS
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Fault assessment - I

• Severity Occurrence Index (SO)
• SeverityPotential harm that fault effect
  inflicts the system Severity is quantified by
  severity scale from 1 to 10.
• Occurrence the frequency of fault occurrence
  during expected operational time interval is
  quantified by by scale from 1 (unlikely to
  occure) to 10 (persistent failure)
• SO index SO Severity . Occurrence

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Fault Assessment II
Severity and Occurrence analysis of the Wheel
system
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Fault Assessment III
Evaluation guidelines and identification of
severe failures that need to be handled
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Fault Assessment List of faults
Periority assignment to different fault types
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Fault Assessment Causality Analysis
Identifying possible causes of failures by
backwardsearch through the Wheel system
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FMEA analysis and Structural Analysis
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Chosen approaches to detailed design (algorithms)
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Supervisory Control - Definitions

• To superviseTo oversee and guide the work or
  activities of a group of people/system, etc.
• Supervision
• Monitoring a physical system and taking
  appropriate actions to maintain the operation in
  the case of faults
• The ability to monitor whether control objectives
  are met. If not, obtain/calculate a revised
  control objective and a new control structure and
  parameters that make a faulty closed-loop system
  meet the new modified objectives. Supervision
  should take effect if faults occur and it is not
  possible to meet the original control objective
  within the fault-tolerant scheme.

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Supervisor Architecture
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Logic realization

• Language approach - a component based method
• State-event machines

Figure- Control system hierarchy consists of four
principle components
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Constructing the logic - Language approach
Fig.1
Fig.2
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Constructing the logic - State-event machines
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Logic design - Knowledge aquisition
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Design Tools and implementaion

• Tools
• Statecharts
• Hierarchy/depth
• Concurrency
• Comunication
• Stateflow (Matlab)
• Beologic (BO)
• Consistency/correctness
• Beologic

• Implementation
• IF-THEN rules
• Object Oriented structure

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Exercise and next lecture

• Exercise
• Objectives
• System analysis and knowledge acquisition about
  faults and their effect on the system operation.
• Consider reconfiguration possibilities
• Next lecture
• Structural analysis approach
• Monitorable vs. non-monitoravble part of the
  systems