风电机组尾流与疲劳载荷关系分析

Analysis on relationship between wake and fatigue load of wind turbines

为了研究风电机组尾流对下游风电机组载荷的影响,假设了几个重要尾流参数:上下游风电机组间距、上游风电机组推力系数、湍流强度等。采用Bladed软件和Matlab幅频程序,分别对1.5与3.0 MW双馈式风电机组进行各参数与载荷响应的关系计算。结果表明:风轮处风速会随着推力系数的增大非线性减小;风电机组处于尾流影响范围内时,在风速和推力系数相同的条件下,通常湍流强度受尾流影响后减小使载荷增大,但当推力系数对载荷的影响起主导作用时,虽然湍流强度受尾流影响后减小但载荷会增大;当风速大于额定风速时,应采用变桨控制减小推力系数,以减小风电机组的疲劳损伤。

With the continuous development of wind power industry, the power record of single wind turbine is constantly expanded, and the scale of wind power generation is becoming larger and larger. For large wind turbines, the wake effect cannot be ignored. It has an important influence on the fatigue load of the wind turbine, and also has a significant impact on the output power characteristics of the wind turbine. In order to study the influence of wind turbine wake on the load of the downstream wind turbine, several important wake parameters such as upstream and downstream wind turbine spacing, upstream wind turbine thrust coefficient and nature wind speed are assumed according to the theoretical results of some researchers. The physical quantity of wake region can be obtained according to the momentum theory. The relation between the natural wind speed, the wind speed and the thrust coefficient can be obtained by calculating the axial thrust based on the Bates＇ theory. The wind speed increases linearly with the natural wind speed, but with the increase of the thrust coefficient, the wind speed of the wind rotor will gradually decrease. When the natural wind speed is fixed, with the increase of thrust coefficient, the wind speed of the wind turbine will be reduced, and if the thrust coefficient can be large enough, then the wind speed of the wind rotor will tend to 0. However, there will be no thrust coefficient greater than or equal to 1 in the actual operation of the wind turbine. Use GH Bladed software to build a model of FL1500/70 1.5 and 3.0 MW doubly-fed wind turbine, and calculate the load response of the wake model to the downstream wind turbine. The conclusions are obtained by analyzing the calculation results which are as follows： 1） When the natural wind speed is constant, the wind speed at the wind rotor will decrease nonlinearly with the increase of thrust coefficient. The wake wind speed increases with the distance between 2 wind turbines, but the trend is gradually stabilized. But for different wind rotor radius, the larger the value, the closer to linear variation the relationship curve of wake wind speed and distance. 2） When the wind turbine is in the influence range of the wake, under the same wind speed and thrust coefficient, the farther the distance, the less the load will be affected by wake. In the case of larger absolute value of turbulence intensity difference, the load difference increases with the decrease of turbulence intensity difference, which is due to that the decrease of turbulence intensity under the wake effects makes the load increase; sometimes the load difference decreases with the increase of the difference of turbulence intensity, which means under the wake effect the turbulence increases and at the same time the load is reduced. The reason is when the turbulence increases, the load increases, but at the same time the wind speed affected by the wake effect becomes smaller, so the thrust coefficient decreases, followed by the decrease of the load. Comparing the turbulence intensity with the thrust coefficient, the reduction of thrust coefficient has a more influence on the load. 3） When the thrust coefficient of the upstream wind turbine increases, the load will increase; when the wind speed is greater than the rated wind speed, the thrust coefficient should be reduced by adopting the pitch control so as to reduce the fatigue damage of the wind turbine. 4） Based on the wind turbine modeling and numerical simulation calculation with Bladed software, the influence of upstream wind turbine wake on the fatigue loading of the wind turbine is discussed. The accuracy of this calculation which is used to determine the load response characteristics of wind turbines is limited, but it is very difficult to carry out on-site verification of the fatigue load data of wind turbine. Therefore, the data provided by the chart in this paper are for reference only.