简化的Schavemaker交流电弧模型参数的计算方法研究

以工业、商业、住宅的电气系统为背景,以建立准确的电弧模型为目的,基于简化的Schavemaker模型进行研究,提出一种基于神经网络的模型参数计算方法。利用基于实验数据的模型参数计算方法得到神经网络训练样本,构建模型参数与工作条件之间的神经网络。利用所建网络可在无法获得特定工作条件下的电弧实验数据时直接预测该工作条件下的模型参数值。最终的验证结果表明,所提出的基于神经网络的模型参数计算方法准确度高,而且相比于现有方法具有一定的优越性。同时也反映了所建交流电弧模型能有效地实现电弧模拟,可为进一步的交流电弧特征学习和检测算法设计提供方法和工具。     

基于时频分析的改进小波包风电功率波动平抑方法

针对传统小波包风电波动平抑方法存在的过度平抑问题,提出一种基于时频分析的改进小波包平抑方法。首先,找出功率最大变化范围超过波动标准的时刻对集合,利用小波包对风电功率进行小波分解得到各频段分量;然后,从高频到低频依次对各频段分量在时刻对集合上进行局部削峰填谷,直到风电功率满足波动标准,从而得到平抑后的风电并网功率和储能功率指令;最后,对波动平抑效果进行评价。算例仿真表明该方法在满足风电波动标准的基础上,减小了储能功率指令的累积功率和充放电切换次数,有利于降低储能配置成本、延长储能寿命。     

综采工作面采空区封闭与惰化防灭火技术的数值模拟

为了验证综采工作面采空区封闭与惰化过程中相关技术参数的合理性,了解注惰过程中各组分气体体积分数分布及扩散规律,掌握其随时间变化特点,依据气流渗透及扩散理论,运用Fluent软件对采空区封闭后惰化过程进行数值模拟,并采用现场取样化验分析的方法对采空区封闭后注惰过程中气体体积分数进行监测.通过对比发现,模拟结果与监测数据基本吻合,验证了模拟结果的准确性.由模拟结果可知：双     

基于SWT的GIS电压互感器二次侧干扰分析

特快速暂态过电压（VFTO）是气体绝缘变电站（GIS）中切换隔离开关时产生的特殊电磁暂态现象。VFTO会以传导和辐射方式影响二次设备的正常运行。为探究VFTO对二次设备的干扰特性,文中采用自制的二次侧干扰测量装置对某1 000 kV GIS的电压互感器（PT）二次侧共模干扰进行现场实测。接着,对比了5种时频分析方法的性能,采用其中性能较优的同步压缩小波变换（SWT）对实测波形进行了时频分析。实测结果表明：PT二次侧的共模干扰电压峰峰值最高可达9.65 kV。微脉冲的时频分析结果表明：7.8 MHz频率分量幅值高,且贯穿波形的始终,是PT二次侧干扰的主导频率分量。该分析结果可为GIS中二次设备的电磁抗扰度测试和电磁防护设计提供参考。     

改进希尔伯特-黄变换分析波磨对列车时频特征的影响

本文旨在研究钢轨波浪形磨损对列车时频特征的影响.建立了车辆/轨道空间耦合模型,模拟计算了钢轨短波、长波波磨激励下车辆系统的动力响应.将集成经验模态分解（Ensemble Empirical Mode Decomposition,EEMD）和正交希尔伯特变换（Normalized Hilbert Transform,NHT）应用于车辆/轨道耦合系统的振动信号分析中,分析了不同波深和波长的波磨对转向架动力响应时频特征的影响.结果表明：波磨会引起车辆系统振动响应的频率调制,频率振幅与平均频率之比可作为轮轨冲击的预警指标.     

应用联合时频分析研究CO2焊接过程中的电信号

CO₂焊接过程的电弧电压、焊接电流信号蕴含了丰富的焊接信息。利用联合时频分析对CO₂焊接过程电信号进行研究,分析了短时傅里叶变换窗函数的选择对谱图的时频集聚性的影响,并选择汉宁窗获得了较好的时频集聚性。为了获得CO₂焊接电信号中短路过渡的信息,尝试利用时频分析谱图对焊接试验中采集到的几组焊接电流信号进行分析,研究了其能量分布及熔滴过渡的特征,并利用联合时频分析三维谱图,对采用不同焊接参数获得的电弧电压信号进行对比。结果表明,利用联合时频分析对CO₂焊接过程电信号进行分析,能够获得更多的有价值信息,该方法具有较好的研究应用前景。     

肌电信号特征提取方法综述

肌电信号分析在肌肉的临床诊断、康复、仿生控制和工程应用等领域具有重要的研究价值,而特征提取是肌电信号分析的基础.文章总结回顾了现有肌电信号特征的提取方法,并将其归纳为四大类:时域分析方法、频域分析方法、时频分析方法和非线性动力学方法.在简单介绍各类特征提取方法的基础上,比较了各类方法的特点与优劣,并对其在肌电分析相关领域的应用前景进行了展望.     

基于参数优化VMD和TET的柔直线路单端故障测距方法

单端行波故障测距方法在考虑频变波速影响时需要提取故障行波时频域特征,但现有方法存在时频分辨率较低、波头识别困难和波速计算不准确的问题。为此,提出一种基于参数优化变分模态分解(variationalmode decomposition, VMD)和瞬态提取变换(transient extraction transform, TET)的单端故障定位方法。首先,利用麻雀搜索算法(sparrow search algorithm, SSA)优化VMD参数,提取含有故障特征的高频模态分量。然后,对该模态分量进行瞬态提取变换,通过去除短时傅里叶变换中模糊的时频能量,保留与信号瞬态特征密切相关的时频信息,得到故障行波时频域全波形。最后,在故障行波全波形中提取主频分量并标定初始波头与第二反射波头,通过计算主频分量下的波速度,结合行波定位方法实现单端故障测距。在PSCAD/EMTDC中搭建四端柔性直流电网的仿真结果表明,所提算法对过渡电阻和噪声具有较强的耐受性,即使在较低采样率下也能实现准确的故障定位。     

Inverting cascade impactor data for size-resolved characterization of fine particulate source emissions

In this paper, the inversion processing of cascade impactor data to construe continuous size distributions within fine particulate matter (PM_2.5) is examined for residential oil furnace and fireplace appliance emissions. Impactor data from tests with these emissions sources are selected for the challenges they pose to comprehending the size distributions of aerosol mass and chemical species. In specific, the oil furnace aerosol offers an opportunity to apply data inversion to study a bimodal lognormal distribution in which much of the aerosol mass is impactor-penetrating nanoparticles . The fireplace emissions on the other hand cover the issue of a chemical size distribution, which is subject to particle loss and characterized by a single lognormal, accumulation mode peak. Computational steps relevant to the application of the data inversion are illustrated in detail. Evaluation of correlation coefficients (0.992) indicates that the inversion model predictions fit the impactor data well. Simulations of systematic measurement error (±10%) at each impactor stage are shown to have a negligible impact on the inversion results for test data. It is concluded that data inversion can be effective when (i) source emissions contain a portion of particles that falls outside the measurement range of cascade impactors, (ii) a mass size distribution of an individual species is determined without the knowledge of the total mass concentration for that species, or when (iii) losses in the particle charger system are significant.     

Temperature effects on the transition from nucleation and growth to Ostwald ripening

Condensation, involving nucleation, growth, and ripening from a metastable state, is an important but complex phase transition process. The effect of physical parameters, including temperature, on condensation dynamics, the competition between homogeneous and heterogeneous (seeding) nucleation, and the separation of polymorphs are among several issues of practical interest. We present a model based on population dynamics that describes the time evolution of the particle size distributions for condensation of the fluid phase and consequent decline in supersaturation. The crucial effect of interfacial curvature on energy, and hence on particle size (Gibbs-Thomson effect), causes larger particles to be less soluble, so that smaller particles dissolve and eventually vanish (denucleate). Numerical solutions of the governing equations show the transition from nucleation and growth to ripening occurs over a relatively long time period. The influence of temperature on these phenomena is primarily through its effect on interfacial energy, growth rate coefficients, and equilibrium solubility. Temperature programming is proposed as a potential method to control the size distribution during the phase transition. The model suggests conditions to suppress homogeneous nucleation by seeding. We also explore how a temperature program for cooling crystallization based on different properties of the crystal forms can separate two crystal polymorphs.