电力系统故障时静止无功发生器的运行分析

静止无功发生器 (ASVG)在电力系统投运之后 ,为了协调装置自身安全及其对系统贡献二者之间的关系 ,必须深入研究系统在故障情况下对 ASVG的影响。用对称分量法给出了电力系统故障期间 ASVG的等效电路。对电路中的主要参数进行了分析。在理论分析的基础上 ,指出了在对称调制方式下 ,通过控制器可以调节流过装置的正序电流以及直流侧电容电压的直流分量 ,而流过装置的负序和零序电流以及直流侧电压的交流分量和装置主电路的参数及其变压器与系统的连接方式有关。     

电力系统故障瞬间静止无功发生器的可控性分析

以 2 0 Mvar静止无功发生器 (ASVG)工业装置的开发为背景 ,分析了电力系统发生故障的瞬间 ,连接于系统中ASVG所受的影响。通过对装置和系统中主要电压和电流矢量的描述 ,并借助数字仿真 ,研究了系统发生故障瞬间 ,ASVG由正常状态进入故障状态的原因。指出在系统中电压(特别是电压相位 )发生变化的情况下 ,可以通过控制以及同步信号的选取 ,使装置在一定程度上避免进入故障状态 ,提高装置在电力系统中的生存能力     

单周控制新型静止无功发生器的应用研究

针对配电网中电能质量低的问题,在无功补偿系统中运用新型静止无功发生器(ASVG)实现无功补偿;在分析单周控制(OCC)技术和单周控制新型静止无功发生器(ASVG)工作原理的基础上,利用单周控制形成的PWM波,对单相ASVG进行控制;设计单周控制的数字控制器,达到系统所需的无功补偿效果.对单相ASVG进行建模以及闭环控制的Matlab/Simulink的仿真,并进行实验验证.实验结果表明该装置在单周控制下,直流侧电容电压在工作过程中波动较小,动态响应速度较快,稳态补偿精度能够满足工程中无功补偿的需要.     

基于IGBT的静止无功发生装置研究

随着电力电子技术的发展，绝缘栅双极晶体管IGBT的容量和耐压有了较大突破。由于IGBT属于全控型器件，因此IGBT构成的新型无功电源具有可靠性高、体积小、控制灵活、调节范围大等特点，这就是新型的无功补偿器ASVG（Advanced static VAR Generator）。该装置通过控制IGBT的通断，在三相之间实现能量交换，从而产生所需无功功率。ASVG感性和客性运行状态均连续快速可调，具有广泛的发展前途。     

区域电网电压无功优化系统对电网的影响

电网无功合理控制是实现电网经济运行的重要手段之一,区域电网电压无功优化通过调度自动化SCA-DA系统采集伞网各节点遥测、遥信等实时数据进行在线分析和计算,在确保电网与设备安全运行的前提下,以各节点电压合格、省网关口功率因数合格、达到最经济运行状况为约束条件,从全网角度进行电压无功优化控制,实现无功补偿设备投入合理、无功分层就地平衡、电压合格,实现主变分接开关调节次数最少、电容器投切最合理、电压合格率最高、输电网损率最小的综合优化目标.系统最终形成有载调压变压器分接开关调节、无功补偿设备投切控制指令,从而实现对电网内各变电所的有载调压装置和无功补偿设备进行集中监视、集中管理和集中控制,实现对电网电压无功优化运行的闭环控制.     

基于IGBT并采用自校正算法的ASVG装置的研制

针对国内外研制的静止无功发生器(ASVG)的现状,介绍了一种基于IGBT智能模块并采用自校正算法的ASVG装置的研制理论和方法.在系统结构的实现上,该装置的主电路采用基于IGBT的智能模块IPM构成三相桥三电平变流器;控制器采用双CPU结构,以DSP(TMSF240)作为主控制器,其任务是采样、计算和实时控制;以80C196作为辅助控制器,专门处理外挂键盘输入、数据显示查询及与上位机通信.在装置的控制策略上,采用电流间接控制和基于自适应的自校正PID调节算法,以实现装置的动态无功补偿.实验结果表明,该装置响应快,精度高,结构简单,易于维护.     

光伏并网发电系统中公共连接点的电压调节

光伏并网发电系统通常应用于薄弱电网末端,输出功率的随机性会造成并网点处电压波动。利用光伏自身无功调节可抑制电压波动。为分析抑制效果,推导出光伏并网发电系统输入电网的有功、无功功率调节范围。当光伏无功调节效果不满足国标要求时,使用超导储能动态电压恢复器(DVR)维持公共连接点(PCC)电压的稳定。采用了PCC电压外环,电容电流内环的双环控制策略,结合空间矢量脉宽调制(SVPWM)对变换器进行控制。仿真结果表明超导储能动态电压恢复器可快速稳定公共连接点电压。     

新型静止无功发生器ASVG及其不对称专家PID控制

论述了ASVG的工作机理和在系统电压对称时的动态数学模型 ,并针对系统电压不对称时ASVG的运行与控制问题 ,分析了系统电压不对称时的被控对象模型 ,提出了恒电压不对称专家PID控制方法 ,给出了系统有1 5 %的负序电压时的仿真结果 .结果表明 :该控制方法可以有效地减少系统电压不对称对装置的影响 ,且装置起动过程超调和输出电压波动小 ,控制灵活 ,具有鲁棒性     

电网调度AVC技术运行维护研究

针对变电站利用人工或电压无功控制装置(VQC)调压存在的弊端，提出采用电压无功自动控制系统(AVC)进行调压的方法，并介绍了AVC系统的技术方案以及在银川智能电网的应用情况.AVC系统利用调度自动化系统的‘四遥”功能，从全网角度进行电压无功优化闭环控制，实现无功补偿设备合理投入和主变分接开关适量调解，有效提高电网电压质量.     

兼顾功率协调控制的两级式光伏逆变器低电压穿越控制策略

为提高基于Boost电路的两级式光伏逆变器的低电压穿越(LVRT)能力,设计了以基于Boost的直流母线电压控制环为核心的兼顾有功、无功电流协调控制的LVRT策略.首先分析了两级式光伏逆变器的常规Boost电压控制模式和输出电流控制策略;在电网电压跌落时,通过引入基于故障前光伏阵列最大功率点电压前馈的母线电压控制外环改变Boost电压控制模式来快速调节光伏阵列的输出功率,以稳定直流母线电压和防止逆变器过流;同时,根据电压跌落深度,按比例减小有功电流id,在保证逆变器不过流的前提下输出无功电流iq,为电网提供无功支撑,以帮助电网故障恢复.最后,利用PSCAD/EMTDC仿真软件搭建100 k W两级式光伏逆变器模型进行控制策略验证,结果表明该策略不仅在电压发生深度跌落时仍能快速、有效地抑制直流母线电压升高,使光伏逆变器安全地实现低电压穿越,而且提高了其在电网故障期间的无功支撑能力.     

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.     

橡胶颗粒沥青混合料低温抗裂性试验研究

以AC-13级配为基础,将橡胶颗粒代替部分集料掺入混合料中,以低温弯曲试验为评价方法对不同橡胶颗粒掺量下沥青混合料的低温抗裂性进行研究,并引入应变能密度值对混合料的低温抗裂性进行综合评价.试验结果表明:橡胶颗粒沥青混合料试件的破坏微应变均超过2 300,满足冬寒区的技术指标;无论是否掺加橡胶颗粒,随着温度的下降,沥青混合料破坏时的最大弯拉强度增大,弯拉应变降低,劲度模量增大;弯曲应变能密度在胶粒掺量为1%左右时具有较大的弯曲应变能密度值,此时橡胶颗粒沥青混合料具有较好的低温抗裂性.     

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-