Environmental Engineering Reference
In-Depth Information
production speed, or the transition at the rated wind speed between the partial and
full load regions (Fig.
11.2
).
Blade pitching is activated only in the full load region, while in the partial load
region the blades are kept at zero pitch angle in order to maintain the maximum
aerodynamic efficiency of the rotor.
11.2.3 Wind Turbine Control
Two control methods for blade pitching are available, the first method is the
collective blade pitching (CBP) which is the process of changing the pitch angle of
all blades in the same time, or in other words, all blades have the same pitch angle
at any time. The second method is the IBP where each blade is set to a different
angle from the other blades. The use of each method depends on the set objec-
tive(s) of the controller in the full load region. If regulating rotor speed is the main
task, CBP can do the job, however, if the task is extended to reduce blade loading
or adapt to the varying aerodynamic loading over the rotor disk, the IBP is the right
candidate [
7
,
14
]. These two control methods pose different performance
requirements over the blade pitch actuators, while the CBP is used to adjust the
blades angles according to the slow changes in the wind speed which might happen
once every few rotations, the IBP requests many adjustments of the blades angles
per each rotation. This difference in performance requirement should be taken into
account when faults are introduced, and in analyzing the results.
The controller design follows the classical linear design methods applied to a
linearized wind turbine model at a number of operating points that spans over the
different operating regions. Due to the change of the turbine characteristics over
the operating regions, the gain-scheduling control methods are used successfully to
control turbines.
The collective blade pitch GSPI is one of the first well-documented controllers
that have been implemented to control floating wind turbines, it is used in the
literature as a baseline controller to compare the obtained results. This work will
follow the same steps and use the baseline GSPI controller to study the blade
pitching system fault effects on the floating turbine.
The GSPI controller is a sophisticated collective pitch controller that employs a
gain-scheduling technique to compensate for the nonlinearity in the turbine by
changing the controller gain according to a scheduling parameter. This controller
was originally developed by Jonkman for the standard land-based 5-MW turbine
[
13
], and later was implemented to the same turbine mounted on the three main
floating platforms [
5
]. The controller has two separate control loops, the first is the
collective blade pitch control loop which employs the gain-scheduling technique to
the proportional integral controller. This control loop is active only in the full load
region. The second one is the generator torque control loop that switches the
objective between the partial and the full load regions. The structure of the
baseline GSPI is shown in Fig.
11.5
.
