升压斩波控制开关磁阻风力发电机系统

为准确地控制发电机的电磁转矩、满足风力发电机组最大功率点跟踪运行要求,提出一种横向磁通开关磁阻发电机转矩控制策略。采用相功率变换器构建励磁与升压斩波电路,可在整个变速运行范围内有效地控制绕组电流的幅值和波形。该变换器通过直流母线与三相逆变器相连,即可构成完整的变速恒频风力发电功率变换装置。样机实验结果表明:采用该方法的风电系统能够将绕组电流限制在±0.5 A域值范围内。从而在转矩/功率控制精度、运行平稳性和直流母线电压纹波等性能上比传统系统更为优越。     

定桨距风力发电机非并网系统内模控制

以定桨距风力发电机为例,对非并网风力发电机的稳定问题进行了分析研究,提出采用内模控制方法消除定桨距风力发电系统本身存在的正反馈效应,设计出稳定的控制系统.在系统中采用检测风速的控制方法,由风速检测值得到转速参考值,根据转速参考值与反馈值之间的误差信号得到发电机转矩参考值,转矩控制系统通过调节其输出端电流控制实际的电磁转矩,使其随参考值变化以实现变速运行.基于实时仿真系统RT-LAB进行了半实物实时仿真实验.实验结果表明:通过内模控制,定桨距风力发电机非并网系统可以在设计风速范围内稳定运行,达到了并网变桨距变速风力机的发电效果.     

开关磁阻电动机电流控制方式的研究

开关磁阻电动机（ＳＲＭ）的输出转矩与绕组电流波形有密切的关系，进行开关磁阻电机驱动系统（ＳＲＤ）的电机本体设计及功率变换器、控制器的设计，必须对绕组通电电流进行深入的研究。同时要使整个系统获得预定的转矩－转速特性，必须对电流进行合理的控制，本文在对开关磁阻电机驱动系统的运行特性进行分析的基础上，深入地研究了电机绕组电流控制方法，这无疑对ＳＲＤ系统的设计与控制有较大的意义。     

无直流电感升压型永磁直驱风力发电系统

针对永磁直驱同步风力发电系统中存在的发电机电流波形差、输出电压低和变换器成本高等问题,提出一种将发电机和变换器一体化设计的新方案。通过引入以永磁发电机电枢电感为升压电感的功率因数校正(PFC)技术,采用平均电流控制法,实现了发电机电流波形与功率因数以及直流母线升压等控制。介绍了新方案的拓扑结构和控制方法,给出了系统工作的参数条件,并搭建了基于dSPACE的快速控制原型实验平台。仿真和实验结果均表明,该方案可稳定提升变换器中的直流母线电压,改善发电机的电流波形及运行功率因数,减小变换器的体积、重量和成本。     

无直流电感升压型永磁直驱风力发电系统

针对永磁直驱同步风力发电系统中存在的发电机电流波形差、输出电压低和变换器成本高等问题,提出一种将发电机和变换器一体化设计的新方案。通过引入以永磁发电机电枢电感为升压电感的功率因数校正(PFC)技术,采用平均电流控制法,实现了发电机电流波形与功率因数以及直流母线升压等控制。介绍了新方案的拓扑结构和控制方法,给出了系统工作的参数条件,并搭建了基于dSPACE的快速控制原型实验平台。仿真和实验结果均表明,该方案可稳定提升变换器中的直流母线电压,改善发电机的电流波形及运行功率因数,减小变换器的体积、重量和成本。     

变速恒频双馈潮流发电机励磁控制技术

基于双馈电机的潮流发电系统是通过调节转子绕组中励磁电流的频率、幅值、相位和相序来实现变速恒频(VSCF)控制的.在分析双馈电机的工作原理和数学模型的基础上,设计了基于定子磁场定向控制的变速恒频双馈潮流发电机的励磁控制系统.在Matlab/Simulink环境中进行了仿真研究,结果表明,采用定子磁场定向控制可实现双馈潮流发电系统定子端口有功功率和无功功率的解耦控制.     

直驱式永磁同步风力发电机不对称故障下的改进控制

在分析直驱式永磁同步风力发电机(permanent magnet synchronous generator,PMSG)全功率变换器功率特性基础上,推导了直流侧电压、并网电抗器功率及网侧输出功率之间的关系,提出了不对称故障下系统的改进控制策略,以实现该型机组的低电压穿越.该控制策略基于电网侧变换器、电机侧变换器功率平衡协调控制思想,将电网跌落信息反馈给电机侧变换器,实现两个变换器的协调控制;同时,在直流侧电压维持在安全范围内的前提下,采用弱控制,以一定的直流侧电压波动为代价,达到消除网侧有功功率2倍频波动的目的.仿真研究结果表明,基于功率平衡协调控制的改进控制策略可较好的实现直驱式永磁同步风力发电机的不对称故障穿越.     

小型风电系统最大功率跟踪的研究

通过对由新型无刷直流发电机构成的小型风力发电系统的分析，提出了一种最大限度获取风能的控制方法，该方法通过控制新型无刷直流发电机的电磁转矩一转速特性间接地控制了风力机的机械转矩一转速特性，使风力机在额定风速以下以最佳尖速比运行，自动跟踪其最大功率点．详细阐述了运用此控制策略的功率调节器的设计方法，并实际制作了100W的功率调节装置．系统实验结果表明，新型控制方法在最大功率跟踪上取得了很好的效果，对提高小型风电系统年发电量有参考和应用价值．     

矩阵变换器供电的交流励磁发电机控制系统的研究

结合交流励磁变速发电机和矩阵变换器的特点,提出了交流励磁变速发电机独立调节定子输出有功、无功功率的控制方案,建立了由SPWM控制电压型矩阵变换器供电的交流励磁变速发电系统的仿真模型,并对系统的功率调节特性以及矩阵变换器作为交流励磁器的供电特性进行了仿真.仿真结果体现了系统良好的特性,证实了矩阵变换器作为交流励磁器的可行性.     

电传动推土机牵引性能匹配的变压控制方法

电传动推土机动力总成包括发动机、发电机、超级电容以及轮边驱动电机,其载荷变化范围大且具有突变性的动力学特征,使发电机与电动机难以实现全局功率匹配.针对电传动推土机动态牵引性能匹配这一关键问题,提出基于双DC-DC(直流-直流)变换器的直流母线电压变压控制方法.即在直流母线与发电机之间加入DC-DC变换器,控制发电机的额定电压工作点,实现发动机在额定工况点工作的高效目标;在直流母线与电动机之间加入DC-DC变换器,根据实时载荷所表达的系统状态变矢量调节变压系数,控制发电机与电动机相对于载荷变化的动力学匹配关系,使发电机与电动机在全载荷意义上实现功率匹配,保证其牵引性能的发挥.通过某型号推土机开发过程性能匹配及其系统数字化模型仿真试验,验证了基于双DC-DC变换器的直流母线电压变压控制方法的有效性.     

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.     

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     

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     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

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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