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RISK ASSESSMENT OF UNDERWATER GLIDERS USING 25
UNCERTAINTY ANALYSIS AND FAULT TOLERANT CONTROL

Figure 2. Way of input to output with faults (Blanke et al., 2006)

Timing of the faults are also important for FTC structure. Abrupt faults occur instantly and can
happen as a result of hardware damage. Incipient faults are the ones that occur or change slowly
with time. Intermittent faults come and go randomly, many time.
Structures of the FTC can be categorized in three main title. Those are embedded systems
approach, distributed diagnostics and remote diagnosis. In embedded systems approach fault
analysis and controller reconfiguration is done on the main control of the system. Main computer
can reach all error information and all algorithms that can be used in faults. Distributed diagnosis
is a structure that distributes information and possible answers to a problem between multiple
systems, linking them to each other. It is used to find fixes to faults that require a lot of
computational work. Remote diagnosis is the last structure type. It uses an on board controller
and an off board controller group. Onboard one has limited power but off board group has a huge
computing power. On board system detects the possible faults while off board group is responsible
for identifying and isolating the fault.

Figure 3. Coordinated diagnosis and remote diagnosis structure (Blanke et al., 2006).

4.2.2 FTC Types
There are mainly two types of FTC. One of them is passive and the other one is the active fault
tolerant control. Passive FTC is also called robust control and handles failures without the need
of a FDI system. It has high reliability for a certain number of faults and uncertainties. In robust
control the worst case scenario algorithms are used. Even in case of a little fault this setup may
cause power degradation in system. On the other hand, robust control gives fast and exact

Sayı 8, 2017 GiDB|DERGi