Publishers version - DTU Orbit

Magnitude (abs)
To: blade pitch
0.05
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
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From: wind meas
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10 0
Bode Diagram
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Frequency (Hz)
From: gen speed
feedback only
typical measurement
perfect measurement
Figure 152: Frequency responses of H2 optimal feedforward (From: wind meas) and feedback
(From: gen speed) controllers for the NREL 5-MW turbine at a 13 m/s wind speed operating
point, with 9 seconds of available preview time.
perfect knowledge of the turbine model.
10.9 Summary
This chapter presented an introduction to wind turbine control using lidar, primarily focusing
on a frequency domain analysis of lidar measurement quality. Two control examples were
included to highlight the challenges that accompany the design of feedforward controllers
that use lidar measurements. A summary of the main results presented in this chapter is
provided here.
• With perfect preview measurements of wind speeds, a model-inverse feedforward controller
can completely cancel the effect of the wind disturbance on a turbine variable
of interest, assuming perfect turbine modeling. For imperfect preview measurements, a
measurement filter can be introduced such that the mean square value of the turbine
variable is minimized.
• A feedforward control system requires not only measurements of the wind disturbance,
but also a certain amount of preview time required for implementation.
• For blade pitch control, the lidar system should be used to acquire an estimate of the
“blade effective wind speed,” a weighted integral of wind speeds along the blade that
describes the equivalent wind speed experienced by the blade. Furthermore, the longitudinal
component of the wind is of interest because it has the greatest impact on the
rotor aerodynamics.
• The two main sources of lidar measurement error are geometry effects, or estimation
of the longitudinal component using a line-of-sight measurement, and wind evolution,
which represents the decorrelation of the turbulence as it travels downwind between the
measurementlocationandtheturbine.Spatialaveraging,inherentinlidarmeasurements,
appears to help with estimation of blade effective wind speed.
• Windturbinecontrolsystemsareoftendefinedinthenon-rotatingframe,whereestimates
of the collective, vertical shear, and horizontal shear wind components are required, as
opposed to measurements of the wind speed at individual blades.
216 DTU Wind Energy-E-Report-0029(EN)
10 −2
10 0