Fault Detection and Diagnostics for Rooftop Air Conditioners

47
current operation point P
1,
P F
1 2
ratio dist
= ) is calculated, and when the distance ratio is
P F
1
1
less than a preset threshold β , then a fault corresponding to the minimum distance will
be indicated. In Figure 3-5, the fault point with the minimal distance for P 1
is F
2
while
for P
7
is F
1, and if the distance ratio is lower than a preset threshold, fault II would be
indicated for P
1
while fault I for P
7
.
The performance of the method is good in that the distance ratio monotonously
decreases with increasing fault level ( P 1
has the same fault level as P 2
and P
4
but a higher
fault level than P 5
and lower fault level than P 3
and P
6
), and is relatively insensitive to
the choice of parameters c ( P 6
can be classified correctly in Figure 3-5) and different
operating conditions over a wide range (refer to Deliverables 2.1.3, 2.1.4 & 2.1.5 and Li
& Braun (2003) for details).
Model Residual-2
True Residual-2
Fault Quadrant II
Fault Quadrant I
F 2 (-c, c)
F 1
( c, c)
P 6
P 3
P 5
P 1
(0,0)
P 4
P 2
M norma
P 7
Model Residual-1
True Residual-1
Normal Operation
Region
Figure 3-5 Distance method for fault diagnosis