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numerous control design specifications in the non-linear and hardly coupled wind
turbine system. To be more precise, one important specification is to mitigate loads
in the turbine components to increase their life time.
This chapter presents different strategies to design robust, multivariable and
multi-objective collective and individual blade pitch angle controllers and gen-
erator torque controllers. These controllers are based on the H ? norm reduction
and gain scheduling control techniques to mitigate loads in wind turbines without
affecting the electric power production. A wind turbine non-linear model has been
developed using the GH Bladed software package and it is based on a 5 MW wind
turbine defined in the Upwind European project [ 1 ]. The family of linear models
extracted from the linearization process of the non-linear model is used to design
the robust controllers. The designed controllers have been validated in GH Bladed
and an exhaustive analysis has been carried out to calculate fatigue load reduction
on wind turbine components, as well as to analyze load mitigation in some extreme
cases.
The presented chapter is divided into four main sections, where the first one is
this introduction. The second section presents general control concepts for wind
turbines and the selected Upwind 5 MW wind turbine used to design the proposed
controllers is briefly analyzed. Also, a baseline control strategy for the Upwind
5 MW based on classical control methods in wind turbines is carefully explained
in this section. The third section shows the process to design the proposed mul-
tivariable robust controllers. These controllers are based on the research presented
in [ 2 ] and they work in the above rated power production control zone. Their
closed loop performance is analyzed in MATLAB. The designed robust controllers
are:
• Generator Torque Controller based on the H ? norm reduction to mitigate the
loads in the drive train and tower [ 3 ].
• Collective Pitch Controller based on the H ? norm reduction to mitigate loads
in the tower and to regulate the generator speed at the nominal value [ 4 ]. The
regulation of the generator speed is improved with a gain scheduling of three
H ? controllers designed in three operating points. The gain scheduling is
developed with a complex problem solved via Linear Matrix Inequalities
(LMI).
• Individual Pitch Controller based on the H ? norm reduction [ 5 ] to mitigate
loads in the tower and to align the rotor plane in the turbine.
The fourth section analyzes simulation results in GH Bladed using the different
designed controllers compared to the baseline control strategy. Fatigue loads in
DLC1.2 case and extreme loads in DLC1.6 and DLC1.9 cases are analyzed [ 6 ].
The last sections summarize the conclusions and the future of the work described
in this chapter.
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