虚拟惯性时间常数对互联电网小干扰稳定影响研究

传统同步发电机的惯性时间常数是不变的物理参数,虚拟同步发电机的推广与应用使得系统惯性时间常数具有可变性和可调性,继而有可能影响互联系统的小干扰稳定性。论文以VSC-HVDC为研究对象,对其进行虚拟同步发电机控制建模,然后基于特征分析法,对等值联网系统求解低频振荡衰减因子的解析表达式,分析了不同场景下惯性时间常数对小干扰稳定水平的影响程度,发现当惯性时间常数与阻尼系数在同一个数量级时对小干扰稳定有较大影响。最后在两区四机经典模型中验证了结论,对于虚拟同步发电机参数整定和研究互联系统的小干扰稳定性分析及控制具有一定的参考价值。

Random forest algorithm for classification of multiwavelength data

We introduced a decision tree method called Random Forests for multiwavelength data classification. The data were adopted from different databases, including the Sloan Digital Sky Survey （SDSS） Data Release five, USNO, FIRST and ROSAT. We then studied the discrimination of quasars from stars and the classification of quasars, stars and galaxies with the sample from optical and radio bands and with that from optical and X-ray bands. Moreover, feature selection and feature weighting based on Random Forests were investigated. The performances based on different input patterns were compared. The experimental results show that the random forest method is an effective method for astronomical object classification and can be applied to other classification problems faced in astronomy. In addition, Random Forests will show its superiorities due to its own merits, e.g. classification, feature selection, feature weighting as well as outlier detection.

基于复特征值分析的某盘式制动器制动尖叫问题改进

以某车型出现2000 Hz制动尖叫问题的盘式制动器为研究对象,建立制动器的有限元模型。通过试验模态对有限元模型进行修正,应用复特征值分析技术,获取系统的复特征值和振型,并通过ODS测试确认与制动尖叫频率对应的不稳定模态。然后针对此不稳定模态,通过相关性分析量化制动器零件对系统不稳定模态的贡献,采用优化具有最大贡献量的零件几何结构来改善制动尖叫。最后通过SAE J2521台架试验验证此方法可行。