Environmental Engineering Reference
In-Depth Information
b
ð
t
Þ¼
b
0
ð
11
:
17
Þ
where b
0
is the seize angle.
11.3.2.3 Pitch Runaway
The complete failure of the pitch sensor in such way that produces a constant value
will make the pitch control loop unstable, and the output command follows a ramp
function forcing the blade to pitch to feather at the maximum rate till it reaches the
maximum range of b
max
¼
90
, then the blade will stuck at this position. This fault
is described as
b
ð
t
Þ¼
min b
ð
TOF
Þþ
b
max
t
TOF
ð
Þ
;
b
max
ð
11
:
18
Þ
b
max
is the
where b
ð
TOF
Þ
is the current pitch angle at the time of fault TOF,
maximum pitch rate, and t is the time.
11.3.2.4 Bias Error
The bias error is a common problem in pitch systems that might originate from
different sources such as a malfunctioning of the pitch sensor measurement (gain
or bias), or a relative blade angle deviation in the rotor (rotor adjustment problem).
When the bias is introduced, the pitch actuator model equation is modified as
b
ð
t
Þ¼
2fx
n
b
ð
t
Þ
x
n
Þ þ
x
n
b
ref
ð
t
t
d
Þ
ð
b
ð
t
Þ
b
bias
ð
t
Þ
ð
11
:
19
Þ
where b
bias
ð
t
Þ
is the bias angle value, which might be constant or depending on
time according to the fault origin.
11.4 Simulation Setup
The state-of-the-art aero-hydro-servo-elastic simulation code FAST (Fatigue,
Aerodynamics, Structures, and Turbulence) is a moderate complexity simulation
code developed by the national renewable energy laboratory (NREL) [
17
]. This
code is used by the research community and industry to analyze the structural
dynamics of the horizontal axis wind turbines. FAST is built up of different
modules such as the AeroDyn module which is used to calculate the aerodynamic
loading of the wind over the turbine structure, the HydroDyn module that models
the hydrodynamic interaction of the platform with waves and current, the Servo-
Dyn model that includes the turbine control system, and the ElastoDyn module
