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Figure 149: Collective flap response to collective wind: dashed line indicates open loop (no
feedback control); each level of preview is indicated by the progression from blue to red.
The notch near 0.7 Hz corresponds to the rejection of 1P loading that is provided by the
augmented dynamics.
in wind speed. This goal is evident in the frequency responses provided in Fig. 149.
10.7.2 Controller Performance Simulations
As shown in Fig. 148, TurbSim is used to generate wind speeds at the turbine that are
consistent with the von Karman spectral model. Then the technique presented in Laks et al.
(2013) is used to induce evolved wind speeds located at 60 evenly spaced azimuths that are at
a measurement radius of r = 15 m (= 75% blade span). The evolution distance d = iTs×U
is chosen based upon i samples at the control system sample rate of 20 Hz (= 1/Ts) and the
nominal wind speed of U = 18 m/s.
The controller is simulated using feedback only, and also with increments of i samples of
preview
Kff = Kw0 ··· Kwi 0 ··· 0 , (243)
up to i = 10 samples. For previews 0 ≤ i ≤ 10, the controller uses gains up through Kwi,
and for i > 10, the controller uses preview gains through Kw10. In the latter case, this is
equivalent to taking measurements further than 1/2 s (at 18 m/s average wind speed) ahead
of the turbine, and then waiting until those wind speeds are within 1/2 s of reaching the
turbine before storing them in the feedforward MEMORY.
ThecontrollerissimulatedusingthesamebaseTurbSimwindfieldfirstusingfeedbackonly,
and then multiple times using feedback plus preview feedforward. For the preview simulations,
evolved wind speed measurements are pre-computed for the base wind field at distances
that correspond to preview times in the range [0.05,10] s (or preview distances in the range
[0.9,180]m). The computationdonefor each distance produces60 time-varying measurement
waveforms arranged spatially in a ring in front of the turbine as depicted in Fig. 133. As
indicated in Fig. 148, the present rotor position θR(k) and speed ΩR(k) are used to predict
1/2 s worth of blade rotation, and then the evolved wind speeds at the 60 azimuth locations
are interpolated to the predicted blade positions. This gives the controller a preview of wind
speeds that the blades will encounter over a 1/2 s horizon.
There are three sets of measurements generated corresponding to (i) an ideal preview
case without evolution, (ii) a set that includes the evolution model, and (iii) a set that
uses evolution and lidar distortion as discussed in Section 10.5. The turbine and controller
simulation is repeated for each set of pre-computed wind measurements and the RMS blade
load and preview measurement error (relative to the wind at the blades) are computed. The
DTU Wind Energy-E-Report-0029(EN) 213