Environmental Engineering Reference
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generator speed in 4.44 % but the loads are increased in the z axis in the different
moments analyzed. The activation of the IPC in C4 reduces the loads in the
stationary hub moment in y axis and tower base moment in x axis in 43.3 and
25.1 % respectively compared to the results using the C2 control scheme. In this
extreme load analysis, the loads in blade root moment in z axis are increased using
the C4 control strategy.
5.5 Conclusions
This chapter proposes one process to design different multivariable robust con-
trollers for load mitigation in wind turbines. These controllers are compared with a
baseline control strategy named C1, which is based on classical control methods
used in wind turbines, not only in the controller design process, but also in the
validation process with different complex analyses from simulations with the wind
turbine non-linear model in GH Bladed. Some conclusions can be extracted from
the work presented in this chapter:
• The control objectives of each control strategy are summarized in Table
5.1
.
The C1, C2 and C3 control strategies need a generator speed sensor and a tower
top accelerometer to use them in the developed generator torque and collective
pitch angle controllers. However, the C4 control strategy also needs blade root
sensors to solve the specific control objectives including the IPC.
• The robustness of the generator torque and collective pitch controllers included
in the C2 control scheme is carefully analyzed in Sect.
5.2
. The mixed sensi-
tivity problems to develop the controller syntheses are explained from the
nominal plants to the definition of the weight functions. The proposed gener-
ator torque and collective pitch blade controllers perfectly mitigate the loads in
the desired components of the wind turbine and they extract the nominal
electric power value during the power production in the above rated zone.
• In the gain scheduled control included in C3 control scheme, the three LTI H
?
controllers are perfectly interpolated without losing the stability and perfor-
mance in all trajectories of the above rated zone solving an LMI system. These
controllers perfectly improve the regulation of the generator speed compared
with the LTI H
?
controller in C2. The parameter adaptation in this gain
scheduled controller is not optimized for gust inputs. Other variables with a
faster response than the pitch angle signal, like generator speed error, can be
taken into account to calculate the varying parameter value to improve the
generator speed regulation in extreme wind gust cases.
• The multivariable robust IPC included in the C4 control strategy satisfies the
proposed control objectives: to reduce the asymmetrical loads which appear in
the rotor due to its misalignment and to mitigate the load in the tower reducing
the wind effect in the tower side-to-side first mode. The load mitigation in the
tower reducing the wind effect in the tower side-to-side first mode using the C4
