大功率高效率无源谐振软开关Boost DC-DC变换器

提出了一种新型的无源谐振软开关Boost DC—DC变换器拓扑,并重点分析了该拓扑结构的7个工作模态和工作波形。通过在常规的Boost电路中增加少量L,C,D器件,使主功率开关管和功率二极管工作在谐振软开关状态,提高了效率和可靠性。用软件Pspice对该电路拓扑进行了仿真,并通过实验得到了基于该电路拓扑研制的90kW DC—DC变换器的主功率器件开关波形。该变换器已经成功地应用在中国第1辆燃料电池城市客车中,各项技术指标均满足使用要求。     

一种TNPC三电平逆变器的零电流软开关技术

为了改善变流器的谐波含量和效率,多电平拓扑被广泛应用于光伏和储能领域.同时,采用软开关技术能够降低开关损耗.针对T型中点钳位式(TNPC)三相三电平结构,提出了一种新型的零电流软开关变流器拓扑.该软开关拓扑每相仅需要额外使用两个辅助谐振开关器件和一条LC谐振支路,拓扑控制简单,不需要改变传统的PWM调制方法,辅管的开通时间只由LC谐振参数决定.就能保证主桥臂和辅助桥臂的开关器件实现零电流转换(ZCT),提高了系统的效率.通过换流过程方程和状态平面图,对所提出软开关技术的工作原理和控制方法进行了详细的分析和推导.通过半桥样机实验验证了所提出软开关拓扑的可行性.     

移相H桥变换器的一种新型软开关拓扑

针对目前软开关变换器拓扑结构复杂、损耗较大的问题,提出移相H桥变换器的一种新型软开关拓扑,基于原有的逆变变压器和整流、滤波元件,增设一种无源辅助箝位电路,拓扑结构简单易行,无需有源器件和附加控制,通过其换流重叠及续流、箝位作用,实现超前桥臂的零电压通断和滞后桥臂的零电流通断,有效地降低变换器损耗和提高系统效率。对新型软开关拓扑进行原理定性阐述,结合各时段波形进行理论分析,得出有关软开关条件。实验结果证实了本拓扑方案及理论分析方法的有效性。     

软开关技术在SRD系统中的应用研究

介绍了软开关技术的基本原理、基本的软开关电路拓扑,提出一种开关磁阻电机功率变换器的软开关方案,该方案在直流电源与相绕组控制电路间插入一种准谐振直流环节电路,并给每个相开关并联电容器后实现了开关磁阻电机功率电路中所有器件的软开关操作.对主电路工作模式进行了分析,并通过仿真验证了所提电路的软开关性能.     

基于移相调功的三电平超音频感应加热电源

多电平逆变器用于高电压大功率场合,可有效解决单只功率开关器件电压及电流定额受限的难题.基于这一优点,设计了适用于负载串联谐振的三电平感应加热逆变电源,给出了三电平逆变电源的拓扑结构,并采用PS-PWM(移相-脉宽调制)输出功率控制策略,在有效控制和调节输出功率的同时,改善了输出电压与电流波形的质量.采用PS-PWM控制方法,在器件额定电压确定时可提高1倍逆变器容量,且输出电压和电流的谐波也明显减少.利用PSPICE对25 kHz、540Vdc的超音频感应加热逆变电源的实际工况进行了仿真,理论分析与仿真结果验证了文中提出的三电平逆变器拓扑结构及功率控制策略的正确与合理性.     

一种软开关式谐波补偿器的仿真研究

选择一种带交流谐振环节软开关谐波补偿器的主电路拓扑,采用正斜率锯齿载波在该拓扑下将所有开关器件的开通动作集中在锯齿载波的垂直沿处,便于软开关动作的实现.对系统进行了仿真研究,仿真结果表明采用该控制方法能实现谐波补偿器全部功率开关器件的软开关动作.     

软开关式谐波补偿器主电路的仿真研究

分析了一种带交流谐振环节软开关谐波补偿器的主电路拓扑。采用正斜率锯齿载波在该拓扑下将所有开关器件的开通动作集中在锯齿载波的垂直沿处,便于软开关动作的实现。对系统主电路Simulink环境下进行仿真研究,仿真结果表明,采用该控制方法能实现谐波补偿器全部功率开关器件的软开关动作。     

矿用移动式逆变电源的仿真研究与分析

通过分析井下电机车照明装置的工作要求和实际使用条件,提出了一种新型移动式逆变电源装置, 对逆变电源的主电路工作原理进行了分析。为了缩短对大功率电子装置的研制周期和减少研制费用,利用MATLAB中的Simulink建立了以IGBT 为开关器件的三相逆变电源仿真模型,并对采用PWM脉宽调制技术的逆变系统进行仿真。根据对输出电压仿真波形的比较和分析,对电路中各元件参数进行选取,仿真模型分别考虑了主电路和控制器模型,较为精确地反映了实际情况,为工程设计提供参考,解决传统工作中地面供电对有用信号干扰大、井下电源不稳定、电流不恒定等问题。     

基于神经元PID控制的四开关三相Buck-Boost逆变器研究

单级四开关三相Buck-Boost逆变器是一种能够在较大直流输入电压范围内工作的新型拓扑结构,除了升压/降压能力外,该拓扑还具有实现DC-AC转换的功能.此外,与传统的四开关三相逆变器相比,该新型拓扑结构获得的输出电压正弦性良好,且不需要任何输出滤波器.新型拓扑结构使用较少的开关器件、电感和电容,从而降低了成本和尺寸....     

改进型基本梯级多电平逆变器

根据基本梯级逆变器提出了一种改进的多电平逆变器电路拓扑,讨论了对其进行谐波消除和幅值控制的方法.该拓扑结构用n个独立电源,2n 4个开关器件可产生2n 1个电平电压;并保留了多电平逆变器开关频率低、效率高等优点,所用器件较少,克服了基本梯级逆变器存在的感性负载时输出电压产生畸变、各独立电源输出功率不均衡等缺点.该逆变器拓扑适合于可再生能源发电的场合.改进前后的拓扑结构在不同负载下的仿真结果表明,该拓扑结构具有可行性.     

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.     

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