风切变和塔影效应对风力机输出功率的影响

Influences of Wind Shear and Tower Shadow on the Power Output of Wind Turbine

以NREL 5 MW风机为例,基于叶素动量理论(Blade Element Momentum,BEM)研究风切变和塔影效应对风力机输出功率的影响。用三阶Taylor展开描述指数型风切变模型;针对现代大型风力机的锥状塔架结构,对塔影效应模型进行适当修正。计算不同来流风速下的输出功率,并从功率波动和周期内平均输出功率两方面研究风切变和塔影效应的影响。结果显示,风切变和塔应效应都是周期性功率波动和周期内平均功率下降(功率损失)的来源。其中塔影效应是功率波动的主要原因,而风切变是功率损失的主要原因。功率损失由风场损失和风轮损失构成,其中风场损失是一个与风轮结构参数及风速轮廓系数相关的常数,而风轮损失与风力机控制策略密切相关,在变桨距控制阶段,风轮损失随风速的增加而增加。

The influences of the wind shear and tower shadow on the power output of wind turbines in terms of power fluctuation and power loss are investigated. Firstly, the wind shear model and the tower shadow model are described in detail. The tower shadow model is modified in view of the cone-shaped towers of modern large-scaled wind turbines. Subsequently, power fluctuation and power loss due to wind shear and tower shadow are analyzed for NREL 5 MW baseline wind turbine with blade element momentum(BEM) theory. Results indicate that the power fluctuation is mainly caused by the tower shadow, whereas the power loss is primarily induced by the wind shear. The power loss can be divided into wind farm loss and rotor loss. The wind farm loss is a constant while the rotor loss is strongly influenced by the wind turbine control strategies. When the variable-speed controller works, the rotor loss stabilizes around zero, but when blade pitch controller works, the rotor loss increases as the wind speed intensifies.