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34 D. ÖZTÜRK and H. AKYILDIZ

afterward making proper move is the premise of fault tolerant control. Fault tolerant is the
property that empowers a system to keep working legitimately in case of the disappointment of
some of its segments. A fault tolerant configuration empowers a system to proceed with its
planned operation, perhaps at a decreased level, as opposed to coming up short totally, when
some of the parts in the system break down. In other words, the system all in all is not ceased
because of failures either in the hardware or the software and the system merges towards an
error free state. In the event that the outcome of a framework disappointment is so disastrous,
the system must have the capacity to utilize inversion to fall back to a protected mode.

Redundant hardware has to be attached to automation for safety critical systems to not be
affected by any failure. Fail operational systems are performed irresponsive to any single
component fault. While a measurement specifies a serious fault, fail safe systems shut down the
main system in a controlled manner. Stability and pre-allotted performance of the control loop is
checked by robust control periodically. However, fault tolerant control checks the system online
and identifies critical faults in the components. Development of fault in the failure will be
preventable in case of identification of the fault. The plant has to be available thanks to the FTC
system in spite of faults. It is possible that performance of the plant may reduce and what is
worse humanity and environment may be damaged. Then, FTC system handles the faults by
system reconfiguration.

FTC systems can be categorized into two groups as active (AFTC) and passive (PFTC). Active
FTC differs from passive FTC in accordance with fault diagnosis and configuration commander
mainly. In PFTCS, controllers are fixed and are designed to be robust against a class off
presumed faults. However, AFTCS responds to system in an active way by reconfiguration so
that stability and acceptable performance of the entire system can be maintained. Moreover,
AFTCS has access to the fault of failure information with FDI before reconfiguration can be
undertaken.

Since the scope of this work on the fault tolerant control, which is an active type of system,
further details on the AFTCS were given just for brief information intended to gain better
understanding of the whole picture. AFTCS reconfigure the control actions effectively. System
performance and stability continues by this means and underperformance can be acceptable in
some cases [2]. AFTCS named as self-repairing at one of the researches which worked on flight
control systems and offered control surface reconfiguration and expert maintenance diagnostics
as a technological development. The other denotation of AFTCS is reconfigurable which
stabilizers closed loop performance despite control effector breakdowns by redistributing force
and moment commands above the disrupted control suite to reduce the effect of breakdown.
Fault tolerant-restructurable control and self-designing control systems are the other denotations
of AFTCS. A real time FDD diagramming which shows the updated information from the
system is important for prospering reconfigurable control systems. Moreover, a controller
design leads to stabilize the system and qualify performance at both normal conditions of the
functions and faulty circumstances in overall systems and also sub-systems. The approach of
fault tolerant control and taken actions should be different for normal and faulty conditions for
certain. Whereas maintaining the quality is the priority in normal conditions, recovery of the
system with well accepted performance becomes crucial. In AFTCS, see Figure 1, the points to
take into consideration are that,

- Design an easy to reconfigure controller,
- Design a high sensitive FDD scheme,

GiDB|DERGi Sayı 7, 2016