Environmental Engineering Reference
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speed is down to zero, so the generator torque is always set to produce the rated
output power. This will lead to a series of acceleration and decceleration of the
rotor due to the induced inflow by the platform pitching and the changes of
generator torque by the torque control loop, resulting in exciting the platform pitch
motion.
The time series of the actuator runaway fault at EC3 are shown in Fig. 11.20 .
Once the fault is introduced at time step TOF, the faulty blade (blade 1) is pitched
at maximum rated to feather leading to gradual decrease of generator speed to
zero. The direct effect of such a fault is clear from the LSS moments, which shows
high transient response with magnitudes up to 3 times the mean LSS moment. The
same transient response is also clear on the tower torsional moment with similar
high magnitudes as in LSS moments. The transient response settles down as the
faulty blade stuck at feather, and the rotor imbalance effects over the turbine
structure starts to dominate.
11.6 Conclusion
This chapter studies the structural loading effects of various pitch system faults in a
floating wind turbine. The considered faults include the bias and gain errors in
pitch sensor measurements, the performance degradation of the pitch actuator, in
addition to the actuator stuck and actuator runaway faults. The simulations use the
utility-scale 5-MW wind turbine mounted on the barge platform model subject to
different wind and wave profiles that correspond to the full load region. The
turbine is equipped with the standard GSPI controller with two control loops,
the first for collective pitch control which is engaged in the full load region, and
the second loop is for generator torque control that switches the control objective
according to the operating region. Different fault magnitudes are also considered in
order to assess the magnitude effect on the turbine. Moreover, different perfor-
mance metrics are used to evaluate the fault effects on the turbine structure.
Regardless of the fault magnitude, LSS moments in addition to the tower
torsional moment are the most affected measures by pitch sensor faults. However,
the effect depends on the fault type, magnitude, and operating condition. While the
pitch sensor bias has the maximum DEL in the middle of the full load region, the
pitch sensor gain fault shows direct dependency of the DEL with wind speed.
Actuator performance degradation has effect on the turbine structure only if the
actuator has very slow response (M3), otherwise, the effect is marginal as the
faulty actuator dynamics are still higher than the turbine dynamics. This result is
strongly related to the type of pitch controller used by the turbine for power
production in the full load region. The implemented strategy employs the col-
lective pitch control concept to pitch the blades away from the wind as the wind
speed exceeds its rated value, which will reduce the aerodynamic efficiency as a
result, and maintain the rotor speed close to its rated value. The used GSPI con-
troller has reduced gains (compared to the gains used for similar controllers of
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