基于多层功率计算的城市轨道交通系统谐波发射水平评估

针对城市轨道交通系统负荷的波动性,提出一种基于多层功率计算的城轨谐波发射水平评估方法。首先,由牵引计算得单列车的功率分布,利用中心极限定理,得单列车功率概率密度函数;然后,结合牵引变带列车个数,通过采用Halton序列的拟蒙特卡洛法分层计算牵引变、主变牵引功率的概率密度函数;最后,综合考虑配电系统谐波,计算城轨系统注入公共连接点的各次谐波电流95%概率值。该方法由中心极限定理求取单列车概率密度,原理简单;利用拟蒙特卡洛方法分层分析城轨系统功率,计算准确;只需列车、变电所的基础电气参数,适用于谐波评估,便于工程实现。利用所提方法计算某地铁线路谐波发射水平,验证了方法的有效性。     

城轨钢轨电位与杂散电流动态分布

城市轨道交通普遍存在钢轨电位与杂散电流异常升高现象,已严重影响城轨供电安全.为阐明城轨钢轨电位与杂散电流动态分布规律,基于城轨供电系统结构建立供电系统动态潮流计算模型,分析多列车、多变电所并列运行下系统潮流动态变化,根据系统节点潮流参数建立钢轨电位与杂散电流的动态分布计算方法,基于列车牵引计算及系统实际参数仿真分析了多列车动态运行下系统钢轨电位、杂散电流分布规律.研究结果表明:列车运行功率重合度对钢轨电位与杂散电流有较大影响,当列车再生功率与牵引功率耦合较大时,回流安全参数会显著升高.为实际系统中钢轨电位及杂散电流控制提供支撑.     

城轨柔性直流牵引供电系统光伏发电并入方式研究

针对城市轨道交通光伏发电功率并网问题,开展城轨柔性直流牵引供电系统光伏发电接入方式研究.基于柔性直流牵引供电系统结构,分析了光伏发电功率不同接入方式及其特点,建立了光伏接入柔性直流牵引供电系统情况下系统动态运行仿真模型,进行了多列车动态运行时光伏发电功率接入的仿真分析,阐明了光伏接入柔性直流牵引供电系统后潮流参数的变化规律及节能效果.研究结果表明,光伏发电并入城轨柔性直流牵引供电系统的功率会优先被附近列车吸收,有效降低了双向变流机组从交流电网吸收的能量,提高了系统运行的经济性.     

极限环解析解确定平衡点吸引域的研究

提出利用系统状态变量两两之间所有极限环的交集,确定高维系统在亚临界霍普夫分岔点附近平衡点吸引域的方法。首先利用改进中心流形降维的方法,对高维微分方程组在亚临界霍普夫分岔点进行降维,得到可进行极限环计算的形式;利用I.Bendxison定理推导极限环存在必要条件的解析表达式,为摄动增量法提供计算初值;然后利用摄动增量和谐波平衡法求取低维系统状态变量在分岔点附近不稳定极限环的近似解析解,用原变量替换近似解析解中的变量得到原系统变量的极限环;最后,将某一变量与其它所有变量形成的不稳定极限环投影到二维平面上取其交集,交集的边界即为该变量的稳定边界。该方法能够精确有效的分析算例中参数大幅变化下亚临界霍普夫点附近平衡点吸引域。     

基于单纯形法的城轨列车惰行点搜索

对电气化铁路的节能技术,解决的方案通常为优化牵引运行策略、再生制动和能量存储系统.为提高单列车区间运行牵引能源利用效率,有效的做法是合理设定区间运行时间,适当减少牵引能源消耗.惰行控制是平衡运行时间和能源消耗的一种通用方法.然而,在应用系统实际情况的约束下,确定合适的惰行点并不容易.针对城市轨道列车区间运行,介绍了基于单纯形法的搜寻合适惰行点的方法,考虑在特定运行时间下,借助于单列车仿真系统的帮助,研究这种启发式搜索法在确定惰行点方面的可行性和性能表现.     

城轨牵引永磁同步电机驱动系统效率优化控制

针对城轨牵引内置式永磁同步电机直接转矩控制(IPMSM-DTC)系统存在谐波电压电流,引起电机铁芯损耗和铜损,降低系统运行效率的问题,提出基于开关频率优化的效率优化控制策略,选择自适应滞环宽度,采用零矢量象限间交错分布的优化方法,利用功率器件开关频率,优化PWM脉冲序列中零矢量;开发基于STM32F103嵌入式微控制器的效率优化控制系统.实验结果表明:该方法可以抑制逆变器输出电压电流谐波,减小开关次数,降低开关电流,从而减少电机铁芯损耗和铜损,提高系统效率,并改善系统的动态性能.     

北京地铁亦庄线列车节能驾驶研究

降低列车牵引能耗是减少城市轨道交通系统耗能的重要途径之一,单列车的牵引能耗由列车在站间的驾驶策略决定,因此,本文以北京市地铁亦庄线为例,介绍了地铁列车的节能驾驶研究.首先调研并收集了亦庄线线路、运营、车辆、供电、能耗等数据,掌握了亦庄线整体节能背景.然后结合地铁运营的特点,给出了北京地铁亦庄线能耗评估的3个指标.并以蚁群算法为核心,开发了列车驾驶的仿真系统,该仿真系统以收集到的亦庄线实际运行数据为输入,离线优化列车自动运行(Automatic Train Operation,ATO)的推荐速度曲线和控制策略.最终将优化后的ATO控制策略在亦庄线进行夜间实验,结果显示,优化后的列车ATO控制策略可以减少单车运行能耗5.67%.     

城轨列车车载储能系统功率需求的动态模糊优化控制方法研究

针对城轨列车复合储能系统中超级电容与锂电池联合供电的功率分配问题,提出了一种考虑系统功率需求的多元化输入的模糊能量控制方法 .为了更好地解决车载储能系统非线性和能量的控制问题,以城轨列车的需求功率、车载储能系统的锂电池和超级电容SOC、锂电池功率分配系数为输出,建立多输入单输出的车载储能模糊控制器,对车载复合储能系统进行建模和仿真.通过利用Simulink进行仿真,结果表明：该模糊控制器能够较好地分配能量,满足列车运行中的功率需求,减少大电流对锂电池的冲击,提高锂电池的循环利用次数,有利于提高列车运行的稳定性和舒适性.     

城轨交通超级电容储能系统变增益控制方法研究

在城轨交通中使用超级电容储存列车再生制动能量可实现良好的节能和稳压效果.本文分析了牵引供电系统、列车、双向DC/DC变换器和超级电容的特性,由此建立了超级电容储能系统模型,并根据所建立的模型探讨了牵引网电压和占空比对系统动态性能的影响.分析表明,牵引网电压和储能系统占空比分别影响了储能系统的内环和外环动态性能.提出了储能系统内环和外环变增益控制策略,消除了上述两变量对系统动态性能的影响.仿真和实验结果验证了所提出的控制策略的有效性.     

基于相关向量机的光伏系统谐波发射水平评估方法

城市配电网的高电缆化率,光伏系统接入时易引发谐波谐振问题;光伏系统并网运行时会向电网注入谐波,造成谐波污染。提出了一种基于相关向量机回归的光伏系统谐波发射水平计算方法,首先建立光伏电站诺顿等效电路;将公共连接点测量数据作为输入向量,利用相关向量机回归模型得到系统谐波阻抗,进而计算光伏系统谐波发射水平。克服了支持向量机方法,其核函数必须满足Mercer条件、参数难以确定等问题。仿真分析和实测数据计算验证了所提方法的有效性。     

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