Environmental Engineering Reference
In-Depth Information
x 10
6
(a)
(b)
0.4
2
0.3
0.2
1.5
0.1
0
1
−0.1
−0.2
0.5
−0.3
0
−0.4
0
4
8
12
16
20
24
28
0
4
8
12
16
20
24
28
V
[m/s]
V
[m/s]
Fig. 10.6 Operating conditions for a wind-driven DFIG: a Ideal power curve: active power (P
e
)
versus wind speed (V). b Slip (s) versus wind speed (V)
to some grid codes, the resulting power changes (that are related to both the
generator torque and speed) must be smaller than 0.1 p.u./min (see p. 122 of [
23
]).
We can expect that, if the sensor FDI system can cope with such fast operating
point variations, it will achieve good performance for slower variations as well.
Changes in the generator speed X
g
are depicted in the form of slip changes in
Fig.
10.7
a. We can see that a wide range of operating conditions are covered. The
first 6 s of the simulation correspond to supersynchronous operation (s \ 0), at
t = 6 s the machine drifts toward synchronism (s = 0) and at t = 8 s the machine
is forced to operate at subsynchronous values of speed (s [ 0).
Three faults are simulated, each affecting one of the three sets of sensors
measuring, respectively i
r
;
abc
, v
s
;
abc
and i
s
;
abc
, as presented in Fig.
10.7
b. First,
between t
¼
1 s and t
¼
2 s, a fault of 5 % in the sensor
' ¼
8 occurs, which
corresponds to the measurement of i
r
;
b
. Recall that the rotor currents are not
monitored. Then, between t = 4 s and t = 5 s, a fault of 2 % in the sensor
' ¼
1
occurs, which corresponds to the measurement of u
s
;
a
. Finally, between t
¼
8
:
5s
and t
¼
9
:
5 s, a fault of 5 % in the sensor
' ¼
6 occurs, which corresponds to the
measurement of i
s
;
c
.
The applied changes in the reference of T
g
and the resulting generator torque is
depicted in Fig.
10.8
a. The reference of the stator reactive power Q
s
is set to zero
for the first 8 s of simulation, and at t = 8 s, a step change of 0.05 [p.u.] is made,
as presented in Fig.
10.8
b.
In both the controlled variables, T
g
and Q
s
, the effect of the additive faults are
clearly noticeable. The presence of bias in the measurement of a stator or rotor
three-phase signal produces oscillations in the dq components of the measured
signal. These oscillations have a frequency equal to the frequency of the faulty
stator or rotor signal. Since the dq components are used for computing the control
law as well as the controlled variables, oscillations around the reference value of
both T
g
and Q
s
appear in the presence of the faults.
