Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology
Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology
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基于线性发电机技术的海上波浪能转换器中传感器测量的时间序列、时频和频谱分析
DOI：
10.4236/epe.2013.51009
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
M. Leijon
中科院分区：
文献类型：
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作者：
E. Strömstedt;A. Savin;O. Svensson;M. Leijon
2009 年 3 月在瑞典西海岸 Lysekil 研究基地启动的第二个实验性波浪能转换器 (WEC) 内部安装了许多传感器系统，用于测量 WEC 及其机械子系统的机械性能。其中一个测量系统由 7 个激光三角测量传感器组成，用于测量直接驱动中活塞杆机械引入传动装置的相对位移。本文提出了两个相隔 2.5 个月的测量周期。发射后两周进行一次测量，发射后三个月进行另一次测量。在同时测量的不同传感器之间进行比较和关联。研究噪音水平。讨论了过滤以进一步细化激光三角测量传感器信号，以便将噪声与实际物理位移和振动分开。测量结果包括活塞杆机械引入的相对位移、气隙中的磁通量、WEC 结构中的机械应变、转换器位置和活塞杆轴向位移以及有功交流功率。通过特写对时域测量、快速傅里叶变换 (FFT) 频域以及短时傅里叶变换 (STFT) 时频分析进行研究，以绘制测量中的频谱内容。终点停止影响在时频分析中清晰可见。研究 FFT 幅度谱以识别其他振动中的齿槽带宽。发电机齿槽效应、定子中阻尼力和洛伦兹力的波动是有区别的，并且根据平移器速度而变化。齿槽振动似乎在测量早期存在，而在测量后期则不那么明显。通过与发电机停机时的噪声和发电机内的振动源进行比较，可以识别磨损引起的振动频率。结论是，移动平均值是时域中足够的滤波器，用于进一步分析活塞杆机械引入传动装置的相对位移。
Inside the second experimental wave energy converter (WEC) launched at the Lysekil research site on the Swedish west coast in March 2009 a number of sensor systems were installed for measuring the mechanical performance of the WEC and its mechanical subsystems. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Two measurement periods, separated by 2.5 month, are presented in this paper. One measurement is made two weeks after launch and another 3 months after launch. Comparisons and correlations are made between different sensors measuring simultaneously. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period. Vibration frequencies due to wear are recognized by comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is a sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.