两种逆变器电源对三相异步电动机性能影响的分析

分析了两种逆变器— 180°导通型和 12 0°导通型输出的非正弦电源作用于电机时产生的磁势谐波 ,给出了电机k次谐波等值电路 ,在此基础上 ,从电流、转矩、损耗等方面讨论了非正弦电源对电机性能的影响。     

导通角可调节的晶体管三相逆变器

晶体管逆变器比起可控硅逆变器来优越得多。本文介绍一种控制电路简单的晶体管三相逆变器。它利用电压—频率变换器的锯齿波作为控制信号,使导通角θ可在120°—180°之间连续可调,并通过分析求出了谐波失真最小时的导通角。     

可控硅在直流电动机无级调速中的应用

可控硅具有功率大，效率高，体积小，重量轻，无噪音，控制灵敏等优点，而且还具有使用小电流，小功率来控大电流大功率的特点，其应用范围。前途都非常广泛。如果在可控硅处于正向阳极电压时，在控制极上加正向脉冲号，就可使可控硅触发导通，如改变触发电压出现的时间，改变触发电压的相位（移相），就可控制可控硅的导通时间，使得输出电压的平均值改变，以实现直流电动机的调速。     

革新与发明

三相电机全能保护器分延时线路A和控制线路B两部分。A部分由单结晶体管BT、单向可控硅McR、三个电阻、两个电容等元件组成;B部分由三个晶体三极管BG_1、BG_2、BG_3,两个电流互感器L_1、L_2,一个继电器J、一个电位器X_1及三个电阻等元器件组成。A部分避免起动电流对电网的影响;B部分保护电机不受过载和电压变化等所损害。其原理是:电路接通,A部分开始工作。电容C_4经R_5充电,C_4两端电压逐渐上升,当升到BT管峰点时BT管导通,在R_7上产生一个脉冲输出电压,触发可控硅MCR导通,构成控制线路B的电源回路,B方开始工作,电机起动,避免起动电流的冲击影响。电机工作正常时,因为三相电机有一相导线穿过控制电路B中的电流互感器L_1、L_2,L_1、L_2上的感应电压经全波整流后分别加到晶体三极管     

SCR—D速度自适应控制系统的研究

转速、电流双环调速系统受以下三种动态参数变化的影响.(1)负载的变化;(2)电流断续时,可控硅电源放大倍数和时间常数的变化;(3)励磁电流的变化.在恒定工作条件下,假设可控硅的触发脉冲幅值为U,宽度为λ,周期为T的三角形电压脉冲,则可控硅——直流电动机系统的传逆函数为     

可变电抗式电机软启动器研究

针对感应电机起动电流大的问题,提出应用可变电抗式软启动器降低起动电流．建立了软启动器的数学模型,通过分析晶闸管导通角与电机电流之间的关系,得出了晶闸管导通角与电机电流的数学解析表达式,为降低起动电流提供一定的技术支持．     

正弦型高功率因数GTO串级调速装置

在提高常规串级凋速装置的功率因数的基础上,研究了能降低逆变电流中谐波成分的逆变控制方案。使用GTO代替常规逆变器中的可控硅,借助次谐波PWM技术选择最佳开关点,并使逆变器触发角a基180°-270°内变化,则能抑制逆变器的谐波电流,还能提高逆变器的功率因数。这套装置用于串级调速的实验表明:电流超前型的功率因数比滞后型的有明显提高,逆变电流中低次谐波大大减少。     

微机监控系统中光照强度无级变化的双向可控硅电路

本文提出应用微型计算机驱动双向可控硅无级控制的一种方法,该方法与常用的单结晶体管触发电路相比,其控制线性好、精度高导通角为180°,便于计算机控制且保证了微机系统的安全。     

玻璃纤维生产线温度自动控制系统

本文论述了玻璃纤维建筑材料生产中温度自动控制系统电路的构成和工作原理。用双向可控硅组成交流调压电路,用KC05可控硅移相触发集成电路控制可控硅的导通角,调节预置电位器可以选择输出电压或电流,并自动稳定系统的输出电压或电流,以便间接控制和稳定熔炼坩埚或拉丝铂管内的作业温度。     

开关磁阻电机数字调速系统

本文介绍一种开关磁阻电机的数字调速系统，调速原理是导通和关断时刻可控的脉冲控制和电流幅值可控的斩波控制．系统用单片微机等组成控制电路，用功率晶体管模块等组成驱动电路及保护，具有调速精度及效率较高、线路简单可靠等优点．     

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.     

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.     

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     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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Brief Introduction to “Journal of Jilin University( Science Edition) ”

<正>"Journal of Jilin University(Science Edition)"is a comprehensive academic journal in the fields of science sponsored by Jilin University and administrated by the Ministry of Education of the Peoples Republic of China.The journal started publication in 1955.The original name at starting publication was"Journal of Natural Science of Northeast People University",which was changed into"Acta Scientiarum Naturalium Universitatis Jilinensis"in 1958 owing to the name change of the university.The present journal name has