Digital Signal Processing Reference
In-Depth Information
(a
)
Ω
1
Ω
2
(b
)
Ω
1
Ω
2
(c)
Decision
support
1
Boolean
threshold
Fuzzy
threshold
X
0
Fig. 11.9 Fuzzy threshold for overlapping hypotheses: a ideal decision space division b real
situation with overlapping of sub-regions c traditional and fuzzy thresholds
μ
Classical
setting
Fuzzy
setting
I
I
1
I
pick-up
I
2
Fig. 11.10
Classical and fuzzy overcurrent decision threshold
As an example of single-criterion protection the fuzzy overcurrent principle can
be used (Fig.
11.10
). Instead of classical decision threshold I
pick-up
one can pro-
pose a fuzzy curve, that separates the blocking and tripping regions in a smooth
way. Unambiguous decision (with the degree of confidence 1.0) can be taken for
current magnitudes lower than I
1
and higher than I
2
, whereas for the values within
the range (I
1
, I
2
) appropriate value of the membership l from the range (0, 1) is
assigned, coding the grade of the signal membership to the category of fault cases.
The higher the membership value l, the more clearly (with higher certainty) the
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