直流微电网协调控制策略研究

直流微电网以其可靠性高、便于控制、损耗低等优点成为未来家庭的主要供电结构.本研究针对目前已有直流微电网控制策略的不足,研究了基于直流母线信号(DC Bus Signaling,DBS)的控制策略,该控制策略可以最大程度地提高新能源的利用率,采用直流母线信号实现直流微电网的最优控制;通过研究直流微电网的下垂控制实现了同一个电压等级下多个微源的功率分配及电压控制;通过研究各微源变换器的输出特性,实现了储能单元及并网变换器的下垂控制与恒功率平滑切换的控制方法;最后在MATLAB/Simulink中搭建了基于平均模型的直流微电网的仿真模型,对孤岛运行时的控制策略进行了验证,仿真结果表明所设计的控制算法能够实现直流微电网的协调控制.     

微电网超级电容器混合储能系统控制策略

光伏微电网有离网与并网2种工作模式。在离网模式下由于负荷及可再生能源的功率变化使得直流母线电压产生波动,在并网模式下会因输入功率变动以及非线性负载产生的低次谐波等使并网电流脉动较大,影响电能质量。本文利用超级电容器和蓄电池组2种储能组件构成微电网混合储能方案,使微电网在离网运行时利用超级电容器的快速响应来补偿瞬态功率,从而更快地稳定直流母线电压;并网运行时在传统并网的电压电流双闭环控制策略中,增加超级电容器电流控制环,降低并网时的电流脉动。对混合储能控制方案进行了仿真和验证,结果表明,提出的混合储能控制策略可以使直流微网母线电压的波动控制在5%以内,并且使并网电流总谐波失真维持在7%左右,从而达到控制目的。     

无功动态补偿的光储微电网并网控制

针对由用户侧无功负荷变化导致的光储微电网并网点电能质量变差的问题,同时为降低系统复杂度,提出一种自然坐标系下无功动态补偿的光储微电网并网控制策略。该策略以蓄电池的荷电状态切换变流器的控制方法来维持直流母线电压的稳定。针对不同的工况条件设计了两种具有无功动态补偿功能的并网逆变器功率控制策略,实现并网点电压的稳定,同时,在自然坐标系下实现了并网逆变器有功、无功功率的独立控制,省去了坐标变换和电网相位检测。实验结果表明,所提出的控制策略可以实现光储微电网系统功率的平稳有效流动,达到无功补偿的目的,且具有较好的动态响应。     

复杂环境中直流微电网母线电压的控制策略

有效的母线电压稳定控制策略是直流微电网在复杂的环境中稳定且安全运行极其重要的保障.以小型直流微电网为研究对象,基于开关表以直流母线电压为控制信号,建立了各接口网侧变换器分段调节母线电压的直流微电网母线电压控制策略,并作了仿真研究.结果表明:基于开关表的直流微电网母线电压控制策略可以实现直流微电网母线电压的稳定工作,保证该系统可以在孤岛、并网等运行环境下稳定工作,研究结果对于保证直流微电网在复杂的环境中稳定且安全运行具有实践价值.     

基于鲸鱼算法改进下垂控制的微电网平滑切换策略

在传统下垂控制所在微电网系统负载发生突变时，可能无法维持整个微电网的稳定；在模式切换过程中存在功率振荡、母线电压偏离过大等问题.针对此类问题，提出一种基于鲸鱼算法改进下垂控制的方法.依据电压幅值及频率波动，应用鲸鱼算法调整优化相应参数；将优化结果反馈到下垂参数计算中，用于解决切换时产生的功率振荡及频率偏移问题；搭建MATLAB/Simulink模型进行仿真验证.仿真结果显示：优化后的算法能够减少功率振荡幅度及频率偏移，实现微电网的孤网与并网平滑切换.在负荷突变工况下，功率偏差最大为13.78%,改进后降至3.97%,从扰动至稳定状态所用时间缩短了37.52%,提高了系统的供电质量，证明了该改进控制策略的有效性.     

SSTS和UPQC在微电网控制中的应用

针对微电网并网过程中存在的电能质量问题,提出了基于统一电能质量调节器(UnifiedPowerQuality Conditioner,UPQC)的微电网并网系统.通过优化选择UPQC的安装位置来改善电网电压波动对微电网并网的影响,改善电网的电能质量,同时通过设定UPQC的控制策略实现微电网的智能孤岛和无缝重连.研究结果表明:所提出的微电网UPQC系统可以工作在并网运行、孤岛运行和重连运行3种运行模式,通过固态转换开关(Solid-state transfer switch,SSTS)的合理切换可以实现3种运行模式的平滑过渡,而且在切换过程中不仅避免了直接切换导致的冲击暂态,也有效地改善了电能质量.在微电网并网模式和孤岛模式之间切换的过程中可不中断微电网的连接,实现了微电网的无缝切换,简化了并网逆变器的控制.     

基于源-荷-储的直流微电网系统协调控制

针对孤岛下独立运行的直流微电网,为了更好的维持系统功率的供需平衡,快速平抑母线电压的波动。利用超级电容和蓄电池的互补特性设计混合储能系统,在下垂控制的基础上,通过增加二次补偿装置抑制负荷功率波动,从而实现直流微电网的精准控制,将系统划分成多个模式运行,通过利用所提的控制策略对各个模块进行联动控制,实现系统平滑的在多个运行模式下切换。完成直流微电网的源-荷-储协调优化控制。最后对其在MATLAB/Simulink上进行仿真实验,验证控制策略的有效性和可行性。     

低压直流微电网母线电压控制策略

直流母线电压恒定是直流微电网运行控制的目标之一,考虑直流微电网并网和离网两种运行模式,提出基于交流电网和储能电池的直流母线电压控制策略.合理设计AC-DC变换器和DC-DC变换器的电压外环和电流内环控制参数,提高控制系统的动态性能,维持直流母线电压恒定,实现系统功率平衡流动.搭建直流微电网的Simulink模型,验证母线电压控制策略的有效性.结果表明当直流微电网系统内的负载波动时,母线电压控制策略可快速保障直流母线电压恒定,验证了提出的母线电压控制策略的有效性.     

微电网主从控制建模仿真

考虑到微电网内分布式电源和负荷所具有的分散性,根据分布式电源的类型以及与储能装置的不同组合方式,采用不同的控制策略分别进行了相应控制器的设计.基于下垂特性的Droop控制可实现负荷功率变化时不同分布式电源间变化功率的共享,而电压/频率(V/f)控制和Droop控制均可在微电网孤岛运行时为微电网系统提供频率支撑;PQ控制可根据实际运行情况实现分布式电源有功和无功功率的指定控制.根据不同电源特性针对性地采用不同控制技术组合,并对微电网孤岛运行模式和并网运行模式之间切换的运行特性进行分析,获得了微电网中相应分布式电源的功率、电压、电流及系统频率的变化规律,证明了PQ-V/f以及PQ-Droop综合控制策略的正确性和有效性.     

基于虚拟同步机控制技术的交直流互联电力系统电压稳定控制策略

电压暂降是电力系统正常运行过程中一种不可避免和难以预测的电能质量问题.交直流微电网和交直流配电的发展,使交直流互联方式下交流电网电压稳定问题更加复杂.针对电压暂降治理,提出了一种采用虚拟同步发电机技术的交直流互联方法.根据本文提出的方法,光伏发电和电池储能等直流分布式系统,能自主地参与到对交流电网电压的调节中,从而维持交流母线电压的稳定性.设计并搭建了额定功率为120kVA的仿真平台,对上述控制策略进行了仿真分析和研究,仿真结果验证了所提出控制策略能确保交流母线电压在电网电压暂降早期不会出现较高幅值的跌落,并在电网电压暂降故障排除后较快地恢复其额定幅值.     

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.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

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.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

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.     

海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

《Chinese Science Bulletin》SUBJECT INDEX TO VOLUME 59(2014)

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Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to