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

2. 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

4. FTC development procedure - I

5. FTC Development procedure - II

6. Fault Modelling

7. Failure Mode and Effect Analysis -FMEA FMEA scheme for the Wheel system

8. FMEA – Other examples FMEA scheme for the GPS

9. 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

10. Fault Assessment II Severity and Occurrence analysis of the Wheel system

11. Fault Assessment III Evaluation guidelines and identification of severe failures that need to be handled

12. Fault Assessment – List of faults Periority assignment to different fault types

13. Fault Assessment – Causality Analysis Identifying possible causes of failures by backwardsearch through the Wheel system

14. FMEA analysis and Structural Analysis

15. Chosen approaches to detailed design (algorithms)

16. Supervisory Control - Definitions • To supervise:To 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.

17. Supervisor Architecture

18. Logic realization • Language approach - a component based method • State-event machines Figure- Control system hierarchy consists of four principle components

19. Constructing the logic - Language approach Fig.1 Fig.2

20. Constructing the logic - State-event machines

21. Logic design - Knowledge aquisition

22. AAUSAT-II example • Process starts with defining • Mission objectives • Mission modes • Control modes • The priority of the modes are established

23. AAUSAT-II example

24. AAUSAT-II example • Generating the boolean strings for the magnetorquer system The prioritized representation becomes

25. AAUSAT-II example • Building the decision logic for the supervisor Where ’*’ means a chosen logical string The mission is defined by where

26. AAUSAT-II example • The operator involvment can be represented by introducing additional logic

27. Tools Statecharts Hierarchy/depth Concurrency Comunication Stateflow (Matlab) Beologic (B&O) Consistency/correctness Beologic Implementation IF-THEN rules Object Oriented structure Design Tools and implementaion

28. 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