Abstract
Lidars have gained a lot of popularity in the field of wind energy, partly because of their potential to be used for wind turbine control. By scanning the oncoming wind field, any threats such as gusts can be detected early and high loads can be avoided by taking preventive actions. Unfortunately, lidars suffer from some inherent weaknesses that hinder measuring gusts; e.g., the averaging of high-frequency fluctuations and only measuring along the line of sight). This paper proposes a method to construct a useful signal from a lidar by fitting a homogeneous Gaussian velocity field to a set of scattered measurements. The output signal, an along-wind force, acts as a measure for the damaging potential of an oncoming gust and is shown to agree with the rotor-effective wind speed (a similar control input, but derived directly from the wind turbine’s shaft torque). Low data availability and the disadvantage of not knowing the velocity between the lidar beams is translated into uncertainty and integrated in the output signal. This allows a designer to establish a control strategy based on risk, with the ultimate goal to reduce the extreme loads during operation.
Highlights
There has been a lot of interest in using lidar for wind energy in the recent years, for example to assess the energy yield on a site or to validate a turbine’s power curve
We propose a method to assess the severity of an oncoming gust
The ten-minute mean hub height wind speed measured at the r = −140 m range gate was about 13.3 m/s with a longitudinal turbulence intensity of 5.9%
Summary
There has been a lot of interest in using lidar for wind energy in the recent years, for example to assess the energy yield on a site or to validate a turbine’s power curve. Another very promising application is in the form of lidar-assisted control systems to reduce the loads on turbines during operation. Knowing what to expect allows a controller to anticipate any strong perturbations (e.g., gusts), for instance by preventively lowering the thrust on the rotor by pitching the blades. A study by Schlipf et al [5] showed a 51% reduction in loads resulting from an extreme operating gust as prescribed by the International Electrotechnical Commission (IEC) [6]
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