Environmental Engineering Reference
In-Depth Information
5.3.2 Closed Loop Analysis of the Designed Robust
Controllers
The closed loop analysis is an important step before including the designed con-
trollers to work with the wind turbine non-linear model. Some control structures
based on the designed controllers in this chapter are proposed to be analyzed not only
in this closed loop analysis, but they will be also analyzed in the simulations shown in
next section with the non-linear model. In all structures, the control strategy in
the below rated zone is the same (baseline) but they present important differences
in the above rated zone. These control structures in the above rated zone are:
C1
Baseline control strategy based on gain scheduled PI pitch controller with
DTD and TFAD filters
C2
Robust control strategy based on two MISO H
?
MISO LTI controllers: H
?
Pitch Controller and H
?
Torque Controller (see Fig.
5.15
)
C3
Robust control strategy based on two controllers. The generator torque control
is the same as in C2. However, the collective pitch control is based on the gain
scheduling of three H
?
controllers via LMIs resolution (see Fig.
5.15
)
C4
It is an extension of the C2 robust control strategy with an extra-pitch angle
contribution in each blade from the MIMO IPC H
?
IPC (see Fig.
5.14
)
The first analysis of the closed loop studies the output sensitivity function of the
generator speed regulation loop. Table
5.3
shows the peaks and the bandwidth of
this function in different operating points with the collective pitch angle controllers
included in the control strategies C1, C2 and C3. The gain scheduled controller
provides a larger bandwidth in the output sensitivity function, mainly at parameter
values between -4 and 4, with an interesting decrease of the output sensitivity
peak in all operational points. This is a good performance from a load mitigation
point of view in wind turbines, mainly for extreme changes of wind.
The damping of the drive train mode is very important and it can be developed
using the baseline DTD filter in C1 or with the H
?
Torque Controller in C2, C3 and
C4. Figure
5.16
shows the bode diagram of the response of the generator speed from
the generator torque control signal with these generator torque controllers in the
operating point of 19 m/s. The drive train mode is perfectly damped with C1 and C2.
Figures
5.17
,
5.18
,
5.19
and
5.20
show the wind effect in different controlled
signals of the wind turbine with the different control schemes at the operating point
of 19 m/s. Figure
5.17
shows the wind effect in the generator speed. The regulation
of this variable is better using the C3 control strategy at 19 m/s operating point due
to the high bandwidth of this control loop (Table
5.3
). Figure
5.18
shows the mit-
igation of wind effect in the tower fore-aft first mode with the C1 and C2 control
strategies. Figure
5.19
shows the ability of mitigating the wind effect in the tower
side-to-side first mode with a generator torque control in C2 control strategy or with
an individual pitch controller developed in the C4 strategy. Finally, Fig.
5.20
shows
the regulation of the rotor tilt moment using the IPC included in the C4 control
scheme. Similar regulation is achieved in the rotor yaw moment with this strategy.
