Control reconfiguration is an active approach in control theory to achieve fault-tolerant control for dynamic systems. 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 prevent failure at the system level. In addition to loop restructuring, the controller parameters must be adjusted to accommodate changed plant dynamics. Control reconfiguration is a building block toward increasing the dependability of systems under feedback control.
The figure to the right shows a plant controlled by a controller in a standard control loop.
The nominal linear model of the plant is
The plant subject to a fault (indicated by a red arrow in the figure) is modelled in general by
where the subscript indicates that the system is faulty. This approach models multiplicative faults by modified system matrices. Specifically, actuator faults are represented by the new input matrix , sensor faults are represented by the output map , and internal plant faults are represented by the system matrix .
The upper part of the figure shows a supervisory loop consisting of fault detection and isolation (FDI) and reconfiguration which changes the loop by
choosing new input and output signals from {} to reach the control goal,
changing the controller internals (including dynamic structure and parameters),
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.
Alternative scenarios can model faults as an additive external signal influencing the state derivatives and outputs as follows:
The goal of reconfiguration is to keep the reconfigured control-loop performance sufficient for preventing plant shutdown. The following goals are distinguished:
Stabilization
Equilibrium recovery
Output trajectory recovery
State trajectory recovery
Transient time response recovery
Internal stability of the reconfigured closed loop is usually the minimum requirement.
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