多相异步电机谐波电流与谐波磁势的对应关系

为了分析定子绕组流过非正弦电流时多相异步电机的运行性能,必须了解谐波电流与谐波磁势的对应关系。通过Fourier级数把非正弦电流分解为基波电流和一系列谐波电流,分别计算各次时间谐波电流所产生的不同次空间谐波磁势,得到谐波电流次数与产生的合成谐波磁势次数间关系且给出通用表达式。结果表明:多相异步电机谐波电流与谐波磁势间的对应关系不同于三相异步电机。分析了某十二相异步发电机未能建立基波电压却建立了谐波电压的原因,并提出了解决方法。     

PMSM矢量控制下逆变器母线电流频谱分析

逆变器直流母线电流频谱的准确解析是对电磁干扰进行分析及母线电容选取的重要理论基础。针对永磁同步(PMSM)作为负载时逆变器直流母线电流频谱的数学表达和理论求解方法分析了相电压基波和高次谐波对应的等效阻抗。分析得出:非凸极PMSM各次谐波对应的视在电感相等并且恒定;凸极式PMSM的基波电流可以在直轴和交轴上进行相量分解,其对应电感为直轴和交轴电感,高次谐波对应的电感随着转子的位置变化。理论计算时可以通过忽略高次谐波或取平均电感的方法来进行近似。给出了母线电流频谱计算的方法与过程。仿真和实验都证明了本文给出的计算方法及公式的正确性和有效性。     

永磁电机矢量控制下逆变器母线电流频谱分析

逆变器直流母线电流频谱的准确解析是对电磁干扰进行分析及母线电容选取的重要理论基础.针对永磁同步电机(PMSM)作为负载时逆变器直流母线电流频谱的数学表达和理论求解方法分析了相电压基波和高次谐波对应的等效阻抗,结果表明:非凸极PMSM各次谐波对应的视在电感相等并且恒定;凸极PMSM的基波电流可以在直轴和交轴上进行相量分解,其对应电感为直轴和交轴电感,高次谐波对应的电感随着转子的位置变化.理论计算时可以通过忽略高次谐波或取平均电感的方法来进行近似.给出了母线电流频谱计算的方法与过程.仿真和实验都证明了本文方法及公式的正确性和有效性.     

磁势自平衡回馈补偿式直流传感理论研究

研究了一种新型直流传感机理与方法，包括磁势自平衡回路和补偿回路两个环节．分析了磁势自平衡回路在半个周期内单铁心磁势自平衡的工作过程．通过对铁芯的磁化过程、剩磁特性及线圈的激磁状态研究，分析了半波磁势自平衡直流传感器的电流波形．该系统结构简单，稳定可靠，在40％～100％额定电流范围内，输出电流的相对误差不超过0．1％，其精度大大提高．     

基波磁势自平衡串并联混合有源电力滤波器

研究了基波磁势自平衡串并联混合有源电力滤波器.其串联在系统和谐波负载之间的零磁通变流器可自动实现对基波呈现低阻抗,对谐波呈现高阻抗,并可实时方便地检测出剩余谐波电流流过变流器时产生的谐波电压降.通过逆变器产生一个与检测到的谐波电压成正比的谐波电压源,并通过耦合变压器与无源滤波器串联之后再并联接入电网,从而更好地减少流入系统的谐波电流.实验结果证明了结论的正确性.     

电力系统谐波和基波无功检测改进方法

准确、快速地检测电网电流中的谐波成分,是谐波抑制和无功补偿的关键．在小波分析的基础上,结合瞬时无功功率理论,提出了一种谐波和基波无功检测的改进方法．该方法能检测各次谐波和基波无功分量,且运算过程可用软件来实现,不必依赖昂贵的元件和复杂的电路．Matlab仿真结果表明：该方法能实时检测谐波电流和基波无功电流,且检测精度高,动态相应快．     

不连续模式的PWM型DC/DC变换器的广义平均法

在统一模型的基础上，将多频平均方法应用于不连续电感电流导电模式开关变换器。利用这一方法，不仅可以得到稳态时的基波，而且可以得到各次谐波的大小。实例仿真表明，本方法具有计算精度高、逻辑性强、编程容易的优点，适用于开环和各种闭环控制系统的稳态求解和纹波分析。     

谐波、间谐波参数实时检测新算法

在谐波、间谐波参数实时检测的基础上,提出了一种新的电力系统谐波和间谐波参数估计算法.根据正余弦函数的特性,将各次谐波分量变换成直流分量,经由低通滤波后估计其有效值和初相角;从原信号中去除基波和谐波分量,再通过幅值谱最大值搜素获取间谐波频率及有效值和初相角.仿真研究表明,算法精度较高,实现简单,动态跟踪特性好,适合于离散频谱电压、电流信号的谐波、间谐波参数实时估计.     

基于神经网络的电力系统谐波测量方法研究

提出了一种新的基于三角基函数神经网络的电力系统谐波测量方法,给出了该神经网络算法的收敛定理,并采用加窗插值算法修正基波频率的准确度．该方法不需要同步采样和整周期截断,可一次性获得电力系统基波及各次谐波的频率、幅值和相位．计算机仿真结果表明,该方法计算精度高,计算量小,收敛速度快．     

基于改进Hilbert-Huang变换算法的电气化铁路谐波检测

通过对电力机车负载电流进行仿真建模,得到电力机车在不同工况下的电流波形;使用改进的Hilbert-Huang变换算法对电流波形进行谐波检测;采用限制带宽经验模态分解算法对原始电流波形进行分解;通过引入屏蔽信号来控制本征模态函数的带宽,以有效抑制模态混叠.结果表明,所提出的改进Hilbert-Huang变换算法能够有效检测电气化铁路负载电流中各次谐波随时间变化的特征.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that