Control reconfiguration

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Control reconfiguration is an active approach to achieve fault-tolerant control. It is used when severe faults, such as actuator or sensor outages, cause a break-up of the control loop, which must be restructured to become functional again. In addition to loop restructuring, the controller parameters must be adjusted to accommodate changed plant dynamics. Control reconfiguration is a building block towards increasing the dependability of systems under feedback control.


Reconfiguration Problem

The figure below shows a plant controlled by a controller in a standard control loop. The upper part of the figure shows a supervisory loop consisting of fault detection and isolation (FDI) and a reconfiguration which changes the loop by

  1. choosing new input and output signals from the available inputs   to reach the control goal,
  2. changing the controller internals (including dynamic structure and parameters),
  3. adjusting the reference input  .

 

To this end, the vectors of inputs and outputs contain all available signals, not just those used by the controller in fault-free operation.

Reconfiguration Approaches

  • Fault hiding,
  • Linear model following,
  • Optimisation,
  • Learning Control.

Mathmatical Tools

  • Adaptive control (AC)
  • Disturbance decoupling (DD)
  • Eigenstructure assignment (EA)
  • Gain scheduling (GS)/linear parameter varying (LPV)
  • Generalised internal model control (GIMC)
  • Intelligent control (IC)
  • Linear matrix inequality (LMI)
  • Linear quadractic regulator (LQR)
  • Model following (MF)
  • Model predictive control (MPC)
  • Pdeudo-inverse method (PIM)
  • Robust control techniques

Prior to control reconfiguration, it must be at least determined whether a fault has occurred (fault detection) and if so, which components are affected (fault isolation). Preferably, a model of the faulty plant should be provided (fault identification). These questions are addressed by fault diagnosis methods.

fault accommodation is another common approach to achieve fault tolerance. In contrast to control reconfiguration, accommodation is limited to internal controller changes. The sets of signals manipulated and measured by the controller are fixed, which means that the loop cannot be restructured.

Acrticles

  • Y. Zhang, J. Jiang, Bibliographical review on reconfigurable fault-tolerant control systems, in Proceeding of the SAFEPROCESS 2003: 5th Symposium on Detection and Safety for Technical Processes, Washington D.C., USA, pp.265-276, 2003
  • R. J. Patton, Fault-tolerant control: the 1997 situation, in Preprints of IFAC Symposium on Fault Detection Supervision and Safety for Technical Processes, R. Patton and J. Chen (editors), Kingston upon Hull, pp. 1033-1055, 1997
  • H. E. Rauch, Autonomous control reconfiguration, IEEE Control Systems Magazine, vol. 15, no. 6, pp. 37-48, 1995
  • H. E. Rauch, Intelligent fault diagnosis and control reconfiguration, IEEE Control Systems Magazine, vol. 14, pp.6-12, 1994

Books

  • M. Blanke, M. Kinnaert, J. Lunze, M. Staroswiecki, Diagnosis and Fault-Tolerant Control, 2nd edition, Springer 2006
  • T. Steffen, Control Reconfiguration of Dynamical Systems, Springer 2006
  • M. Mahmoud, J. Jiang, Y. Zhang, Active Fault Tolerant Control Systems - Stochastic Analysis and Synthesis, Springer 2003