三相异步电动机制动机械特性的研究

三相异步电动机的机械特性难以利用数学模型进行计算,本文利用MATLAB软件中的动态仿真工具SIMULINK构造了三相异步电动机的仿真模型,并对电机的制动特性进行了具体的仿真研究。结果表明该方法可方便快捷地建立模型,仿真结果直观明了,解决了以往电机实验中的许多难题。     

三相异步电动机动态特性的模块仿真

根据三相异步电动机的名牌数据来对其动态特性进行仿真研究。为此，首选推出了三相异步电动机在同步速坐标系下的动态特性数学模型，并引用了根据电机的铭牌数据来计算其参数的公式，以确定该动态数学模型中的各个参数值，这些参数包括电机定、转子的自感、电阻和定、转子间的互感，然后将该动态数学模型和参数计算公式相结合，建立了异步电动机动态特性的模块化仿真模型，编制了仿真软件，动态数学模型中的微分方程采用四阶龙格-库塔法求解。最后通过实例仿真电机的动态起动特性（Te-s曲线和I-s曲线）从而验证了该模型和仿真软件的正确性，为电机制造部门和使用部门分析三相异步电动机的动态特性提供了一个有力的工具。     

三相异步电动机变参数仿真模型

应用交流电机统一理论，在异步电动机线性化仿真模型的基础上，考虑挤流效应对参数的影响以及主漏磁路的饱和对电抗的影响，建立了变参数仿真模型，并对三相异步电动机的起动过程进行了仿真计算。     

基于晶闸管移向控制的给水泵电机重载启动

针对三相异步电动机启动时,启动电流大,母线压降过大的问题,设计了一种针对重载启动的软起动控制系统。首先,基于电机控制理论,设计软起动控制系统,搭建脉冲发生模块、三相调压模块和PID(Proportional-Integral-Derivative)闭环,对异步电机机端电流和电压进行闭环控制;其次,基于Simulink软件,根据黑龙江省某燃煤机组给水泵电机实际数据,搭建软起动控制模型,进行仿真分析;最后,进行现场测试,测试结果与仿真结果相似,结果表明该模型可在重载启动的情况下,有效限制异步电动机启动电流,减小给水泵电机启动对母线上其他设备的影响,为异步电动机重载启动提供参考。     

基于LabVIEW的三相异步电动机动态过程仿真

文章利用三相异步电动机在二相静止坐标系α、β下的数学模型,建立了基于LabVIEW的三相异步电动机的动态仿真模型,并进行了实例仿真。仿真结果表明,采用该动态模型可以客观、准确、方便地获得三相异步电动机的各项性能指标,可用于对三相异步电动机的各项研究中。     

异步电动机在不对称电压下运行时的性能变化

分析了三相异步电动机在不对称三相电压下运行性能(电机定子电流、电磁转矩和效率)的变化情况,结果表明,三相异步电动机在不对称电压运行时,至少有一相电流超过额定电流,电机转矩减少和效率降低。总结了不对称电压对电动机危害的一些情况,给出了电机运行时对三相电压对称度的要求。     

基于自适应神经模糊Petri网的电机故障诊断

为了提高电机的维护效率,实现电机实时故障诊断功能,基于传统Petri网理论、模糊理论和神经网络算法,提出了一种具有自适应性的神经模糊Petri网故障诊断方法。首先,利用高斯函数代替变迁可信度,解决故障传递不确定性的问题,结合BP神经网络对参数进行适应性训练。然后,根据Petri理论,引入竞争算子对矩阵推理方式进行改进,结合Sigmoid函数,提高了算法的计算效率。最后,以三相异步电动机为例,根据三相异步电动机的故障运行机理和故障特性,建立系统模型并进行故障诊断。仿真结果表明,该算法能准确地诊断出三相异步电动机的故障,具有较好的准确性和适应性。     

三相异步电动机启动常见问题及启动方式

在生产企业中,为了能够安全顺利的生产,减少经济损失和保证电机操作人员的人身安全,电机启动前应对电机进行系统的、全面的安全检查和必要维护。当然,企业应该严格要求电机操作人员,电机操作人员必须具备一定的专业知识,企业也应对电机操作人员进行定期的培训和考核。本文论述了三相异步电动机启动时发生绕组烧毁的原因和三相异步电动机启动时的基本问题以及三相异步电动机的启动方式。     

变频调速异步电动机的特性分析

在异步电动机等效电路的基础上,分析了当电源频率改变时,电机等效电路中主要参数的变化规律及转矩变化情况.根据变频电机的设计思想,设计了一台变频调速三相异步电动机,并对其进行了试验与分析.     

实施中小型三相异步电动机“目标能效限定值”的技术要素

阐述了造成中小型三相异步电动机各种损耗的原因,提出了降低电动机各种损耗的具体措施,并论述了应用优质电工钢片的基础上对电机整体进行重新设计是实施中小型三相异步电动机＂目标能效限定值＂的有效措施。     

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