Implementation and Evaluation of Wind Turbine Control Concepts

Abstract

Wind turbines used in the electricity production nowadays are extremely large systems. Due to the increased sizes of the wind turbines, varying loads affecting on the turbine have became more significant. These changing loads are mainly caused by the variations in the wind speed experienced by the turbine. Wind shear, describing the increase in the wind speed from bottom to upper in the height, can be regarded as the main reason to the changing loads of the blades and the top of the turbine. This loading can be alleviated significantly by individual pitch control, which means that the pitch angle of each blade is controlled individually; in a way that aerodynamic force is kept constant during a revolution. In the commercial wind turbines, collective pitch control is used to limit the output power of the turbine above the rated wind speeds and the turbines are already equipped with individual pitch actuators. This makes the implementation of individual pitch control rather simple. In addition to the wind shear, tower shadow, describing the decrease in the wind speed experienced by the blade when it is directly in front of the tower, has also some impact on the wind turbine loading.

The scope of this thesis is on the pitch control of the wind turbine blades. However, wind turbines and wind characteristics as well as the wind turbine control in general are discussed briefly at the beginning of this thesis. Simulations within this thesis are made for the NREL’s 5 MW reference turbine by using the wind turbine simulation software FAST. Simulations can be divided into three different topics. First, performance of the collective pitch controller in the extreme wind conditions as well as the effect of wind shear on the wind turbine loading in the case of this controller are evaluated. Then, different individual pitch control schemes for the wind shear compensation are implemented and evaluated. Finally, the effect of tower shadow on the wind turbine loading is evaluated and different methods striving to compensate it are implemented.

The study indicates that the loads caused by wind shear can be decreased significantly by individual pitch control. All methods described within this thesis are able to alleviate the loading of the blades as well as the static component of the tilt and yaw moments at some rate. On the other hand, fluctuating components of the tilt and yaw moments are decreased only when the reduction of the 2P load component in the blade loads is also considered in the IPC algorithm. On the other hand, comprehensive reduction of the loading caused by tower shadow seems to be challenging. However, the effect of the tower shadow is also less significant than the effect of wind shear. This study has been made as a part of the larger project for the ABB Corporate Research Center in Germany.