【目的】受限于风电机组主轴的结构和尺寸,主轴弯矩测量效果很难与塔筒弯矩测量效果相匹敌。在主轴弯矩载荷标定期间,需要精确评估出风轮自重在主轴应变片安装截面处产生的力矩,才能更准确地测得主轴倾覆弯矩和主轴偏航弯矩。【方法】运用解析几何原理,提出了一种基于优选并进一步改进的三维坐标系的风轮自重主轴弯矩解析方法。先后分析了轮毂自重、叶片自重在主轴弯矩测量截面处产生的力矩。为了解决风电机组主轴倾角的存在影响优选的三维坐标系的问题,提出了一种新颖方法,在改进的三维坐标系中某个特定垂直平面内,将叶片重力矢量的方向旋转与主轴倾角大小相同的角度,显著降低了叶片自重作用的分析难度。分别评估叶片自重在改进的三维坐标系中的各个分量在主轴承截面中心处产生的力矩分量,通过对相同坐标轴线方向的力矩分量进行合成,再应用力矩平衡原理,得到风轮自重在主轴应变片安装截面产生的力矩,进一步获得可以把风轮空转标定期间在空间自由旋转的3支叶片等效成位于坐标系原点处的、以3支叶片自重力矩之和为重力矩的单个质点的简练结论。【结果】在某型风电机组的机械载荷测试项目中,分别应用传统方法和上述标定分析方法,得到的主轴载荷测试结果具有很好的一致性和代表性,并且使用本文研究的标定分析法得到的主轴弯矩测量结果更符合风电机组设计参数。【结论】理论分析和试验结果验证了本文提出的风轮自重弯矩解析方法对主轴载荷标定的有效性和可行性。

Abstract: [Objective] In mechanical load measurement for large-scale wind turbines, main shaft bending moments have less chance to reach a comparable level for tower bending moments, due to the limitation of structure and size of the main shaft. During the load calibration process for main shaft bending moments, moments generated by rotor gravity at the main shaft load measurement section shall be evaluated accurately to measure main shaft tilt and yaw moments with high reliability. [Methods] Based on optimized and improved three-dimensional coordinate systems, an analytic method for main shaft bending moments generated by rotor gravity was proposed, in which the principle of analytic geometry was applied. The contribution of hub gravity on main shaft load measurement section was evaluated as a basis before the focus of blade gravity effect on the same section. To solve the problem of affecting the optimized three-dimensional coordinate system by the presence of main shaft tilt angle, a novel solution was proposed, where the direction of blade gravity vector in the improved coordinate system was adjusted with the same degree as that of the main shaft tilt angle in a specific vertical plane. The gravity vector of a rotating blade in an arbitrary azimuth angle was then decomposed into each axis of the optimized three-dimensional coordinate system. The resulting moment at the section center of main shaft bearing from every gravity component was calculated separately with details before synthesizing results in the same coordinate axis. Bending moment distribution from main shaft bearing center to load measurement section center was obtained by applying moment balance principle for both hub gravity and own gravity of all blades. The combined bending moment contribution by three blades is equivalent to a single mass point with its gravity of the sum of those of three blades. [Results] In a mechanical load test project for some type of wind turbine, the proposed load calibration analysis method was applied, where the results were compared with those by conventional main shaft bending load calibration. The main shaft load results from the proposed method demonstrated representativeness of wind turbine mechanical loads, and coincide with design specifications of wind turbine. [Conclusion] The validity and feasibility of the proposed analytic method for gravity load calibration of main shaft bending moments are verified by theoretical analysis and testing results.