Environmental Engineering Reference
In-Depth Information
Table 10.2
Incidence table using the GOS
r
f
1
f
2
f
3
r
1,1
0
1
0
r
1,2
0
0
1
r
2,1
1
0
0
r
2,2
0
0
1
r
3,1
1
0
0
r
3,2
0
1
0
reactive power Q
s
exchanged between the DFIG and the grid. As is usual for
control purposes, the measured three-phase stator voltages u
s
;
abc
, stator current
i
s
;
abc
and rotor currents i
r
;
abc
are transformed into the appropriate rotating dq frame
by the Park transformation represented by the dq
=
abc blocs in the figure [
21
]. h
s
and h
r
represent estimates of h
s
and h
r
. These two angles are defined with respect
to a suitable reference axis and they fulfill
d
h
s
d
t
¼
x
s
,
d
h
r
d
t
¼
x
r
where x
s
and x
r
are
respectively the stator and rotor signal frequencies. The symbols v and f, indexed
by a signal name, correspond to the measurement noise and the additive fault
affecting this signal, in accordance with the measurement Eq.
10.34
. Finally X
g
denotes the generator speed. The design of the RSC controller is described in
Chapter 5 of [
15
].
Our aim is to design a diagnostic system that detects and isolates faults on
the stator voltages v
s
;
abc
and the stator currents i
s
;
abc
while being insensitive to
possible faults on the rotor currents. This diagnostic system should work properly
in the whole operating range of the wind-driven DFIG. All the fault magnitudes
are expressed as a percentage of the peak value of the signal at the rated operating
point. The nominal faulty situation (minimum fault to be detected) is defined as the
presence of an offset in the stator current (stator voltage) sensor with magnitude
equal to 5 % (2 %). The choice of a lower nominal fault amplitude for the stator
voltage is justified as follows. A fault in the stator voltages not only affects the
computation of the control law since the stator voltages are used for both state
estimation and computation of the stator active and reactive power, but also affects
the estimated angle for the Park transformation which is obtained by a phase-
locked loop/frequency-locked loop. This is the reason why a lower fault magnitude
is considered for the stator voltages than for the stator currents. The error on the
estimated angle for the Park transformation due to a bias or phase unbalance in
the stator voltages has been studied in [
22
]. Finally, a mean detection/isolation
delay of s
'
0
:
04 s is imposed for all six sensor faults.
