同步发电机光控励磁系统的仿真研究

光控励磁系统是一种新型同步发电机无刷励磁控制系统,它是在普通无刷励磁控制系统中用可控器件(SCR或IGBT)取代不可控的二极管整流,并通过光电耦合形式实现对励磁电流的直接控制。在MATLAB/Simulink环境下,对光控励磁系统进行了建模、分析和仿真.结果表明:光控励磁系统对于提高同步发电机的响应速度,改善电力系统的暂态和稳态性能有明显效果。     

基于DSP的参数自适应电机励磁控制系统的实现

在对谐波励磁无刷同步发电机的励磁控制系统进行了综合分析后,设计并实现了一套基于DSP控制的发电机励磁控制系统,对该系统的硬件和软件构成分别作了详细地说明,该系统励磁控制策略采用参数自适应模糊PID控制,对各信号的实时检测采用交流采样方式;该励磁控制系统现场试验的结果证明,系统稳态和暂态性能指标完全符合发电机对励磁系统的要求,并且对各参数量具有很高的测量精度,完全满足各项指标要求。     

交流励磁发电机励磁控制系统的设计

从交流励磁发电机的基本原理出发,分析了基于动态同步坐标轴系的双通道励磁控制方法.利用基于高速数字信号处理器的双中央计算单元(CPU)方案,设计实现了交流励磁发电机的励磁控制系统.针对该控制系统的特点,充分利用了数字信号处理器(DSP)的高速运算能力和方便的外设,合理设计了控制系统硬件和励磁控制算法软件,双CPU工作共同实现了交流励磁发电机的双通道解耦励磁控制.通过实验分析,进一步验证了基于动态同步坐标轴系的双通道励磁控制策略.     

PID控制算法在同步发电机自动励磁调节系统中的应用

发电机励磁控制系统是电力系统控制的重要组成部分,它直接影响着发电机运行的可靠性经济性和系统运行的稳定性。本文在介绍同步发电机励磁调节系统的基础上,提出了PID控制算法,并对PID在同步发电机自动励磁系统中的调节应用作了进一步阐述。     

采样迭代学习发电机的励磁控制器设计

为了提高电力系统的暂态稳定性,采用采样迭代学习方法,在不需要已知被控系统精确数学模型和对机端电压误差进行求导运算的情况下,设计出了一种同步发电机的励磁控制器,给出了励磁控制系统范数形式的收敛条件.研究结果表明:该控制器避免了以往采用PD型迭代学习控制算法的不足,显著提高了同步发电机功角和机端电压的稳定性.该成果不仅解决了在实际应用中迭代学习励磁控制算法的计算机实现问题,而且还将可能成为发电机的励磁控制方式发展的一种趋势.     

同步发电机励磁控制系统的单片机控制

介绍了一种以MSP430系列单片机为核心的全数字同步发电机励磁控制系统。首先分析了同步发电机励磁控制系统的原理,然后给出了同步发电机励磁控制系统的硬件模块化设计,最后给出励磁控制系统的软件设计。该系统易于维护,抗干扰能力较强,运行稳定可靠,可以应用于很广泛的同步发电机励磁控制领域。     

同步发电机励磁控制系统的单片机控制

介绍了一种以MSP430系列单片机为核心的全数字同步发电机励磁控制系统。首先分析了同步发电机励磁控制系统的原理,然后给出了同步发电机励磁控制系统的硬件模块化设计,最后给出励磁控制系统的软件设计。该系统易于维护,抗干扰能力较强,运行稳定可靠,可以应用于很广泛的同步发电机励磁控制领域。     

基于PWM控制的发电机励磁系统

为提高发电机和电力系统的技术指标，将PWM整流技术应用于同步发电机励磁系统，实现了励磁电流低谐玻和励磁功率单元高功率因数转换，提高了发电机供电质量，利用MATLAB平台对系统进行仿真验证。通过与传统可控硅励磁系统对比，采用IGBT实现的PWM励磁系统性能明显提高．结果表明，本设计改善了发电机机端电压波形，功率因数超过0．99，提高了励磁功率单元利用率，减小了励磁电流超调量，同时对抑制输入电流谐波起到良好的作用。     

改进非线性励磁控制系统的电压调节精度

将PID调节输出和NEC非线性控制输出进行综合，提出一种新型同步发电机励磁控制器——PID NEC非线性励磁控制器。仿真结果表明，该励磁控制系统同时具有较高系统稳定性和电压调节精度，并且动态过程响应快，能更好地适应生产实际的需要。     

发电机励磁系统的运行分析

发电机励磁系统是同步发电机的重要组成部分,它是供给同步发电机励磁电源的一套系统。在电力系统的运行中,同步发电机的励磁控制系统起着重要的作用,它不仅控制发电机的端电压,而且还控制发电机无功功率、功率因数和电流等参数。     

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.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

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.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

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     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the