异步电动机直接转矩控制调速系统的计算机仿真

介绍了异步电动机直接转矩控制系统的基本组成和工作原理,采用异步电动机α β坐标系下的数学模型、按照磁链的圆形与六边形控制方法、基于MATLAB6. 5构建了直接转矩控制调速系统的仿真模型,提出了一种新的磁链运行区间判断方法,该方法简单可行、计算量小.仿真结果验证了该模型的正确性和该控制系统的有效性.     

采用多层滞环控制器的电机直接转矩控制仿真

介绍异步电机直接转矩控制基本原理及主要组成模块,对传统的定子磁链滞环比较器和开关状态表进行了改进,采用多层滞环控制器,采用斩波矢量代替反向电压矢量,采用圆形磁链轨迹控制方法.使用MATLAB7.7建立异步电动机直接转矩控制仿真模型,并进行仿真实验.其仿真结果表明该控制模型的可行性和正确性.     

基于加权模型的异步电动机直接转矩控制定子磁链估计

提出了异步电动机直接转矩控制系统中定子磁链估计的加权模型,实现了电机全速运行范围内定子磁链估计的u-i模型和i-n模型之间的平滑切换,并用MATLAB/Simulink对该模型进行了仿真,仿真结果表明,加权模型可以在异步电动机全速运行范围内准确地估计定子磁链,为实现异步电动机的直接转矩控制奠定了基础.     

直接转矩控制的磁链控制方法仿真与分析

以异步电动机直接转矩控制基本原理为基础,利用Matlab/Simulink搭建2种磁链控制方法:六边形磁链控制方法和近似圆形磁链控制方法的仿真模型.通过改变转速给定值,得出在不同给定条件下的仿真结果,并对其结果加以分析.通过2种方法的对比,给出在全速范围内2种控制方法实现平滑切换的仿真模型.仿真结果验证了2种控制方法平滑切换的可行性,对直接转矩控制技术应用于工程技术等方面有一定的实用价值.     

异步电动机自适应矢量控制系统的一种仿真方法

针对异步电动机矢量控制系统在电动机参数变化时性能下降的问题。提出了一种拥有转子磁链自适应观测器的矢量控制方案，设计出转子磁链自适应观测器，构成转速与磁链闭环的矢量控制系统，利用SIMULINK仿真工具建立了仿真模型，并对系统进行了仿真研究，分析结果表明，这种转子磁链自适应观测器的设计方法是有效的。     

异步电动机定子磁链稳态估计

在异步电动机的矢量控制中,需要准确地估计出电机的磁链,通常所用的纯积分方法对异步电机磁链的估计会带来很大误差.通过对异步电动机稳态模型的分析提出了一阶惯性加补偿的方法来代替纯积分算法.利用该算法可以有效估计出异步电动机定子磁链.该算法计算简便,对硬件要求不高,非常适用于高性能的通用异步电动机控制.     

异步电动机直接转矩控制系统的新型建模仿真

在分析交流异步电动机数学模型的基础上,利用Matlab7.0/Simulink软件构建了一个异步电动机直接转矩控制系统的新型模型.对仿真模型中的定子磁链观测器模块进行了描述,并简要说明了空间电压矢量对磁链和转矩的作用及影响.通过对异步电动机进行仿真实验,得到电流、转速、转矩以及磁链的仿真波形.     

低速段异步电动机直接磁场定向控制

为了改善交流异步电动机无速度传感器控制系统低速运行时转速脉动的问题,采用直接磁场定向控制算法.该算法利用电流模型磁链观测器与反电势积分模型相结合的方法对电动机转子磁链的幅值和相位进行检测,并通过电流模型对转子转速进行辨识构成速度反馈回路.仿真结果表明,所采用的异步电动机直接磁场定向控制可以提高电动机的动态响应速度,使电动机有较好的参数不敏感性,能够在低速运行时取得较好的动静态性能.电流模型与反电势积分模型相结合的磁链观测方法,能够使交流异步电动机无速度传感器控制系统在高速及低速运行时都具有良好的动静态性能,增加了电动机的有效调速范围.     

异步电动机直接转矩控制系统的仿真研究

针对异步电机交流调速的特点,利用闭环磁链观测器作为定子磁链观测装置,并应用MATLAB/Sim-ulink作为仿真工具,构建出异步电动机直接转矩控制系统的仿真模型.仿真结果证明了该方法的合理性、有效性.     

Hopfield自适应异步电动机的直接转矩控制

传统的异步电动机直接转矩控制方法中,电动机低速稳态运行时的电磁转矩、定子磁链和定子电流脉动大,严重影响了整个电动机直接转矩控制系统的性能.为此,文中基于Hopfield神经网络理论和异步电动机动态数学模型,提出了基于Hopfield神经网络的改进异步电动机直接转矩控制方法,有效地降低了电磁转矩、定子磁链和定子电流的波动,达到了改善调速系统低速性能的目的.在此基础上,文中还进行了理论建模和仿真计算,仿真结果表明该方法具有良好的鲁棒性.     

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