两级式三相光伏并网逆变器的控制及仿真研究

光伏并网逆变器作为光伏发电系统的核心部分,其直流侧工作电压必须高于电网峰值电压,故光伏发电系统一般采用Boost+逆变器两级式拓扑结构.以两级式三相光伏并网逆变器为研究对象,分析了其工作原理.前级Boost变换器控制实现MPPT控制;后级DC-AC变换器控制采用电压外环、电流内环双闭环控制,实现直流侧电压稳定和单位功率因数并网.最后在Matlab中搭建了两级式三相光伏并网逆变器的仿真模型,仿真结果表明了控制方法的有效性.     

基于PR控制的三相光伏发电并网逆变器研究

在光伏发电并网过程中,为了不影响电网的质量,必须保证光伏发电系统的输出电流与电网电压在频率、相位和幅值上保持高度一致。为了使光伏并网逆变器输出的并网电流满足相关的并网标准,选择合适的并网滤波器以及并网控制策略是关键。为了提高并网电流的质量,减少并网谐波电流对电网的污染,选择带LCL滤波器的三相全桥逆变电路。在并网控制策略上选择基于并网电流和电容电流的双环电流控制,将PR控制引入到双环控制系统中,从理论上分析了PR控制能实现对并网正弦参考电流的零稳态误差跟踪和抗电网电压干扰。将双环电流控制和SVPWM相结合,通过仿真实验证实了系统的稳定性。     

市电和光伏联合供电运行的控制策略研究

针对传统比例复数积分控制只能应用于三相正交坐标系而无法应用于单相坐标系的问题,提出了将广义二阶比例复数积分控制引入到单相并网逆变器的控制中.次单相并网逆变器与电网电压前馈控制和重复控制构成复合控制策略,对市电和光伏联合供电运行系统的能量控制起到较好控制效果.在复合控制策略下,市电和光伏联合供电运行系统可以优先使用光伏,光伏发电量不足时再由市电补足差额部分.这种方法既保证负载用电不断,又能充分利用清洁能源,且光伏侧不会向市电侧馈电,避免对大电网产生谐波污染.本文所建立的基于TMS320F28335DSP芯片的在MATLAB仿真中证明了实现了光伏优先、市电候补来供电的可行性.     

单相光伏并网逆变器滞环电流跟踪控制的研究

研究了3 kW.单相光伏发电并网系统的逆变器滞环电流跟踪控制的控制方法.根据滞环电流跟踪控制的原理,利用MATLAB/SMUUNK,建立光伏发电并网系统的控制模型.通过调整系统参数对并网系统进行仿真,得到并网电流和电网电压波形,使得输出功率因数近似为1,并对波形总谐波畸变率进行了分析,使其满足设计要求.最后,对单相光伏并网逆变器的滞环电流跟踪控制系统进行相关实验测试,所测得的实验数据与仿真结果基本符合.     

基于不平衡跌落的低电压穿越控制策略

目的解决大功率三相光伏并网逆变器在不平衡跌落时网侧电流所产生的畸变及不平衡,保证在电网不平衡下电压的正、负序分量提取的准确性和实时性。方法采用前馈解耦的空间矢量的双闭环控制算法抑制负序电流的控制策略搭建仿真模型。结果提出了基于正、负序d-q坐标系下的二次陷波器滤波法正确提取电网电压的方法。结论实验结果证明,该方法能有效地对正、负序进行分解以及抑制电网不平衡跌落导致的系统的不稳定运行。     

两桥臂交叉解耦不平衡控制策略研究

由于非不平衡控制策略中没有考虑线电压和相电流的相角差,造成三相电网的有功、无功电流无法完全补偿。为了解决这一问题,根据电压电流相角差,推导出单相补偿器中无功参考补偿电流与负载电流的关系,提出一种两桥臂交叉解耦不平衡控制策略,利用多变量滤波器和交叉解耦双复系数滤波器优化锁相环,精确锁定三相不平衡电网的电压频率和相位,对2个单相背靠背变换器的无功电流分别控制,进而利用两桥臂变换器补偿三相不平衡无功。实验结果验证了所提两桥臂交叉解耦不平衡控制策略,可抑制三相有功不平衡及补偿三相不平衡无功,将三相电流的不平衡度从150.0%降低至2.6%,三相电网功率因数从0.257提升至0.997,减少了三相无功补偿器的开关管个数。     

采用分布式算法的多区域电网风-光-储容量优化配置

针对新能源发电在整个电网中渗透率不断提高而造成的电能质量下降、电力系统无法可靠运行等一系列问题，基于随机规划理论，综合考虑风电、光伏等电源以及联络线、储能设备运行约束，以典型新能源出力时序特征序列下平均新能源消纳水平最大为目标，提出了一种计及电网新能源消纳承载能力的多区域风-光-储容量优化配置方法。该方法主要考虑将风电、光伏发电满足负荷需求后的无法消纳量在不超过储能设备容量的前提下进行储电，而储能设备将在新能源发电低谷期提供电能，充分发挥风、光的时空互补性和储能的调峰优势。首先构造了考虑时-空相关性的典型新能源出力时序特征序列不确定集，然后按典型序列将模型进行分解，采用分布式惩罚原始-对偶次梯度算法实现目标函数的分布式优化求解，最后基于IEEE-24、31节点系统进行算例分析，得到风-光-储容量配置结果，并建议多区域电网中储能设备应考虑建设在含有风光装机的区域。仿真结果表明：相比传统集中式优化方法和拉格朗日松弛法，所提分布式优化方法随着电网区域增多，计算效率优势会越来越明显，10个典型序列时所提分布式方法相比拉格朗日松弛法收敛速度提升了57.1%。所提方法可以为考虑新能源随机性的风-光...     

抑制光伏并网电压扰动的配电网储能配置方法

储能可以有效抑制光伏发电接入配网后系统电压的扰动.文中通过分析光伏出力波动时储能对含光伏配网电压调节的机理,建立了光伏出力波动和负荷变化影响下的储能配置需求评估模型,研究了考虑电压约束时不同影响因素作用下储能的配置需求,以及储能投入后对电压的调节效果.仿真分析了光伏接入容量、局部负荷离光伏接入点距离、光伏接入点相对附近变电站距离与储能配置容量的关系,验证了储能在配电网中对电压曲线具有削峰填谷的效应.同时,利用Matlab/Simulink仿真给出了不同情况下具体的储能投入容量及配置建议.     

光伏并网型三相逆变器电流内环及电压内环的数模设计

为了解决能源资源的紧缺现状,光伏发电并网系统得到了长足的发展和广泛的应用。在光伏发电并网系统中,并网逆变器的设计与控制有着至关重要的地位。本文介绍了一种三相三电平逆变器的设计与控制策略,着重介绍了电流内环、电压外环的设计方法,以便对今后光伏并网型三相逆变器数学建模提供一定的帮助。     

光伏发电系统动态离散等值模型研究

可再生能源在新型电力系统中的占比进一步加大，光伏机组并网容量有明显提升的趋势，而不同渗透率下的光伏发电系统动态行为对电网负荷特性产生显著影响，但光伏发电并网动态模型复杂、待辨识参数多，增大了模型实际运用难度.为此，基于光伏电站机理模型，建立光伏发电并网系统的动态离散等值模型，得到光伏发电并网系统的动态离散等值模型的模型参数；并采用IEEE 14节点系统研究不同渗透率下光伏发电并网系统的动态离散等值模型特性.仿真结果表明，光伏发电并网系统的动态离散等值模型能准确描述光伏发电系统的动态特性，且精度高、易于辨识.     

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