Gain Scheduled H Control of Wind Turbines for the Entire Operating Range - Wind Turbine Control and Monitoring - page 89

Three scenarios were simulated to assess the control performance. The first
scenario is aimed at evaluating the performance of the controllers in region 3. To
this end, the wind gust suggested in the IEC 61400-1 standard was used. This gust
is very pitch demanding. The second scenario is mainly intended to assess the
performance of the anti-windup compensator, i.e., the performance in the transi-
tion region. To this end, the wind rise proposed also in IEC 61400-1 standard was
used. The last scenario illustrates the behavior of the controller under a realistic
wind speed profile.
The simulation results obtained in the first scenario are presented in Fig. 4.15 .
As can be seen, the pitch controllers are always active. The H ? controller achieves
better speed regulation with lower pitch activity than the PI controller. The speed
overshoot is 16.86 % in the H ? case and 19.25 % in the PI case. Additionally, the
H ? controller offers smoother responses in output power and shaft torque.
The results obtained in the second scenario are shown in Fig. 4.16 . The wind
profile rising from 6 to 13 m/s in 10 s makes the wind turbine to operate along the
three regions. Again, it can be seen that the H ? controller achieves a better speed
regulation with less pitch activity. Note that H ? with the anti-windup starts
pitching the blades a bit before the PI with classical anti-windup does. The speed
overshoot is 25.49 % in the H ? case and 32.96 % in the PI case. Like in the first
scenario, the H ? controller offers smoother responses in output power and shaft
torque.
The results for the last scenario are shown in Fig. 4.17 . The 10 min wind speed
field was generated with Turbsim [ 18 ]. The 8 m/s mean wind speed was selected
so that the wind turbine operates in all the three operating regions, but most of the
time in the transition one. It can be seen in the figure that the H ? controller
achieves better speed regulation with significant less pitch activity.
4.7 Conclusion
This chapter presents a robust H ? pitch control design for variable-pitch variable-
speed wind turbines operating along the entire wind speed range.
The main nonlinearities of the wind turbine dynamics are either canceled by
inversion or covered with uncertainty so that an LTI H ? controller designed for a
given operating point can be applied to the whole operating locus. The controller
design guarantees robustness against unmodeled dynamics, cancelation errors and
parameter uncertainties.
The system behavior was assessed by numerical simulations of a high-order
wind turbine benchmark under three very demanding scenarios. Under these
scenarios the H ? controller achieves better speed regulation with lower pitch
activity than classical PI control. This lower pitch activity leads to lower
mechanical stress spreading the wind turbine lifetime and also resulting in softer
output power.