孤岛运行下微电网并联逆变器下垂控制策略研究

随着全球能源互联网的发展,微电网也得到了迅速的发展.微电网系统的稳定性和可靠性将直接受到逆变器运行特性的影响.结合微电网的电压、频率、有功功率和无功功率,分析了逆变器下垂控制的运行特性,实现了孤岛模式下微电网并联逆变器的下垂控制策略的优化.通过数学建模并搭建MATLAB/Simulink仿真模型,详细分析了孤岛模式下微电网负载变化时电压和频率的动态特性.仿真结果验证了微电网并联逆变器下垂控制策略优化的正确性和有效性.     

风光储微电网运行特性仿真分析

为研究含风力发电、太阳能光伏发电和储能系统三种类型微源组成的微电网的运行特性,在MATALB软件平台上,建立了基于主从控制的风光储微电网联合仿真模型.以蓄电池储能系统为主控电源,在微电网并网运行时,所有微源都采用P/Q控制;微电网离网运行时,蓄电池储能系统采用V/f控制,支撑微电网频率和电压.然后对微电网并网运行、离网运行及并离网切换过程进行仿真.仿真结果表明:微电网在并网、离网运行模式下能安全、可靠运行,在运行模式切换过程时能平滑过渡.     

分布式可再生能源并网逆变器控制策略研究

为满足分布式可再生能源并网要求,提出一种模拟同步发电机特性的并网逆变器控制策略.引入惯性与阻尼特性,建立了并网逆变器控制策略的数学模型.采用近似同步发电机励磁无功调节、有功频率下垂特性调节,实现并网逆变器在孤岛运行时维持电网电压、频率稳定,在并网运行时实时跟踪有功、无功指令,提高系统的稳定性.仿真结果证明了所提出控制策略的可行性.     

提高电能质量的风柴蓄独立微电网分层协调控制

针对高渗透率间歇性能源和频繁投切的系统负荷对独立微电网运行控制的影响,在充分考虑柴油发电机和电池储能不同控制特性的基础上,提出一种基于不同时间尺度的独立微电网分层协调控制方案,分别设计了基于蓄电池储能的一级控制器和基于柴油发电机的二级控制器来提高系统电压、频率在不同时间尺度上的稳定性.针对较短时间尺度及较小变化幅度的随机净负荷波动,通过改进蓄电池储能系统的P-f和Q-V下垂控制器来提高系统电压、频率的稳定性;而对于变化周期长和变化幅度大的净负荷波动,分别采用比例积分控制器和辅助无功补偿器来实现柴油发电机组对系统频率和电压的无差控制,从而保证系统稳定性.最后,通过对东澳岛风柴蓄独立微电网在不同运行条件下的运行控制结果分析,验证了所提方法的可行性和有效性.     

孤岛微电网分布式协调无功均分策略

针对微电网中采用逆变器下垂控制的分布式电源时难以实现无功出力合理分配,存在无功环流等安全运行隐患的问题,该文提出一种基于有限时间一致性控制的孤岛微电网分布式协调无功均分策略。该方法在无集中控制器的架构下对无功出力进行均分控制,减少系统无功环流,提高电压质量。相较于传统的一致性策略,所提出的无功均分策略的收敛速度更快,能实现收敛时间及速度的优化,且可适应微电网各种扰动。通过在PSCAD/EMTDC中建立孤岛微电网仿真模型,在多种场景下验证了分布式无功均分策略的有效性和适应性。     

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DSP的储能变流器开发

微电网储能系统里的能量转换系统是一个极其重要的组成部分,有充电与电能回网的作用,储能变流器控制系统的性能关系到微电网中储能系统的"稳、准、快"三要素。微网运行时,逆变器并网电压的相位、幅值、频率能否符合并网要求,是否可以实现无缝切换是储能变流器要求状态转换时的必要条件。该文给出了储能变流器的结构,并基于一特定实例,对储能变流器进行了设计,设计了基于DSP TMS320F28335的算法流程图,并且进行了仿真验证。     

低压微电网逆变器并离网平滑切换控制

分布式能源通过电力电子变换器与本地负载、储能设备等相结合构成微电网;并实现在并网、离网及并离网相互切换模式下的稳定运行。采用下垂控制实现微电网离网运行时逆变器输出电压和频率的稳定、并网运行时输出功率的恒定,并且不改变控制方式实现并离网的平滑切换控制。由于传统下垂控制在离网运行时,逆变器输出电压与频率存在一定的偏差;并且为了使逆变器输出阻抗呈阻性以减小控制参数对输出阻抗的影响,采用一种改进的下垂控制策略;并在逆变器双闭环控制中加入虚拟阻抗。仿真结果验证了改进下垂控制策略在离网、并网以及并离网相互切换运行时的有效性,以及相比于传统下垂控制策略的优越性。     

基于电池储能和可控负荷的孤岛型海岛微电网频率协调控制策略

针对以风电和波浪能发电为主电源的孤岛型海岛微电网,提出一种基于电池储能和可控负荷的孤岛型海岛微电网频率协调控制策略。储能元件采用改进的下垂控制实现类似于电力系统一次调频的有差调频,根据其荷电状态及最大充放电功率,动态调整下垂控制运行点以及下垂控制系数,既能将微网频率偏差控制在合理范围内,又能防止电池储能系统过充过放;利用海水淡化负荷的可控性,将频率偏差引入其转速控制环,实现类似于电力系统二次调频的无差调频。在Matlab/Simulink下搭建了孤岛型海岛微电网的仿真模型,并对不同运行场景进行了仿真验证。结果表明,基于电池储能和可控负荷的孤岛型海岛微电网频率协调控制策略可以有效地分配系统功率差额,维持海岛微电网的频率稳定。     

基于MPC的多源孤岛微电网协调控制

含有多种分布式电源(DG)的微电网在孤岛运行时,DG出力的随机性以及负荷的波动性对系统的安全稳定运行带来了巨大挑战。针对含有柴油发电机、光伏发电单元和储能单元的孤岛微电网,提出了各分布式电源的协调控制策略,光伏发电单元采用最大功率跟踪控制以最大限度利用太阳能,储能单元与柴油发电机协调控制以提高系统运行的稳定性。采用模型预测控制策略(MPC)实现并网逆变器的内环电流控制,避免了繁琐的PI参数整定以及PWM调制器的使用,提高了控制器的动静态性能。仿真结果验证了所提控制策略的有效性与可行性。     

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.     

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.     

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.     

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.     

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.     

橡胶颗粒沥青混合料低温抗裂性试验研究

以AC-13级配为基础,将橡胶颗粒代替部分集料掺入混合料中,以低温弯曲试验为评价方法对不同橡胶颗粒掺量下沥青混合料的低温抗裂性进行研究,并引入应变能密度值对混合料的低温抗裂性进行综合评价.试验结果表明:橡胶颗粒沥青混合料试件的破坏微应变均超过2 300,满足冬寒区的技术指标;无论是否掺加橡胶颗粒,随着温度的下降,沥青混合料破坏时的最大弯拉强度增大,弯拉应变降低,劲度模量增大;弯曲应变能密度在胶粒掺量为1%左右时具有较大的弯曲应变能密度值,此时橡胶颗粒沥青混合料具有较好的低温抗裂性.     

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。     

Quantitative trait loci （QTLs） for quality traits related to protein and starch in wheat

Quality traits in wheat （Triticum aestirum L.） were studied by quantitative trait locus （QTL） analysis in a recombinant inbred line （RIL） population, a set of 131 lines derived from Chuan 35050 × Shannong 483 cross （ChSh）. Grains from RILs were assayed for 21 quality traits related to protein and starch. A total of 35 putative QTLs for 19 traits with a single QTL explaining 7.99-40.52% of phenotypic variations were detected on 10 chromosomes, 1D, 2A, 2D, 3B, 3D, 5A, 6A, 6B, 6D, and 7B. The additive effects of 30 QTLs were positive, contributed by Chuan 35050, the remaining 5 QTLs were negative with the additive effect contributed by Shannong 483. For protein traits, 15 QTLs were obtained and most of them were located on chromosomes 1 D, 3B and 6D, while 20 QTLs for starch traits were detected and most of them were located on chromosomes 3D, 6B and 7B. Only 7 QTLs for protein and starch traits were co-located in three regions on chromosomes 1D, 2A and 2D. These protein and starch trait QTLs showed a distinct distribution pattern in certain regions and chromosomes. Twenty-two QTLs were clustered in 6 regions of 5 chromosomes. Two QTL clusters for protein traits were located on chromosomes 1D and 3B, respectively, three clusters for starch traits on chromosomes 3D, 6B and 7B, and one cluster including protein and starch traits on chromosome 1D.     

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.     

The Analects and the Moment in Peking——The influence of a Confucian education system on the personality formation,the way of thinking and the fate of the main characters

0.Preface China has long been boasting of its colorful and immense culture which comprises of Taoism,Confucianism and Buddhism.The interwoven influence among the religions on Chinese way of thinking,on the nation＇s behavior in their social life throughout the long history is beyond list.