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.     

新颖的双馈式风力发电机低电压穿越控制策略

针对现有文献中双馈风力发电机组低电压穿越控制策略存在的缺陷,提出一种新颖的低电压穿越控制策略.在电网故障期间,利用双滞环电流控制器快速的瞬态响应速度和对系统参数变化的不敏感性来抑制转子电路的过电流;在dc-link上采用crowbar技术,吸收转子侧多余能量,防止直流母线电压过高.在Mtalab/Simu1ink平台中构建了所提出的低电压穿越控制策略的动态仿真模型,研究了三种典型电网故障下的低电压穿越性能,验证了所提出的低电压穿越策略的可行性.仿真结果表明所提出的低电压穿越策略抑制了转子绕组的过电流和dc-link的电容过电压,改善了双馈式风力发电机的低电压穿越性能.     

永磁直驱风电机组变流器低电压穿越控制策略

针对永磁直驱风力发电机组低电压穿越问题,对传统的变流器控制策略进行改进.机侧变流器控制在传统策略的基础上加装功率控制器,在电压跌落期间,通过功率控制器减小发电机有功电流输出,从而限制发电机输出有功功率,减轻变流器直流侧压力.网侧变流器控制在传统控制策略的基础上增加了对电网无功补偿的控制,在电压跌落期间,根据国家标准对电网注入动态无功电流.仿真结果表明,在不借助传统控制策略在低电压穿越过程使用硬件辅助电路的情况下,能够直接通过改进型变流器控制策略,实现风力发电机组低电压穿越.     

基于Crowbar的DFIG低电压穿越控制方法研究

针对双馈风力发电机(DFIG)在电网故障期间面临的脱网问题,研究基于Crowbar电路的低电压穿越控制方法。首先,在分析电网电压跌落过程中DFIG暂态特性的基础上,对Crowbar电路进行阻值整定,得到最优的Crowbar阻值范围;其次,根据电网电压跌落状况下DFIG的暂态响应特性,提出了相应的Crowbar电路投切控制方法;最后,在MATLAB/Simulink上对双馈风电系统低电压穿越问题进行仿真研究。仿真结果证明了采取Crowbar电路的必要性与所提出的控制策略的可行性。     

超导储能提高直驱风电系统低电压穿越能力的控制策略

针对电网故障、扰动引起的电网电压跌落给并网运行的永磁直驱风力发电系统带来的问题,应用超导储能系统提高永磁直驱风力发电系统的低电压穿越能力.研究永磁直驱风力发电系统以及超导储能系统的数学模型,设计相应的控制策略.利用Matlab/Simulink工具箱搭建系统仿真模型,给出不同电网电压跌落状况下,添加超导储能系统前后的仿真实验结果,并对实验结果进行对比分析.结果显示,当电网电压跌落时,超导储能系统能迅速平衡直流母线的功率变化,使直流母线电压保持稳定,直驱风电系统低电压穿越能力得到一定的提高.     

不对称电网故障下双馈风电机组低电压穿越方案比较研究

相比于对称电网故障,不对称电网故障在实际电力系统运行中发生的概率更大,其对双馈风电机组(DFIG)的“有害”影响也更大。首先分析了不对称电网故障下双馈风电机组的瞬态特性,继而结合仿真,研究了双馈风电机组各种低电压穿越(LVRT)技术方案在严重不对称电网故障下的运行特性。在此基础之上,对不同的低电压穿越方案进行了深入分析研究,阐述了其运行特点,并进一步探讨了各种低电压穿越方案的经济性,为工程实现各种低电压穿越方案奠定基础。     

基于可调整电阻Crowbar电路的双馈风电机组低电压穿越方法

针对传统固定阻值Crowbar保护电路很难共同抑制转子电流和直流母线电压的升高这一缺陷提出了一种基于可调整Crowbar电阻阻值的双馈风力发电机组低电压穿越方案,建立了可调整阻值的控制策略以及Crowbar阻值的标定方法;采用PSCAD/EMTDC平台,搭建DFIG及电网故障的动态仿真模型,仿真分析了电网对称短路故障期间所提方案的低电压穿越特性;结果表明:可调整电阻Crowbar方案低电压穿越的效果较好,可实现抑制转子电流的升高以及稳定直流母线电压的目的。     

永磁同步风力发电机组的不对称故障穿越控制策略

永磁同步风力发电机组在不对称电网故障下运行,将导致并网电流不对称、畸变,直流母线电压上升并含有2倍工频纹波等问题.为了提高永磁同步风力发电机组在不对称电网故障下的穿越能力,提出一种PMSG机组的控制策略:在网侧换流器的控制中采用电网负序电压前馈的方法来消除并网电流负序分量;在机侧换流器的控制中提出了一种新的发电机电磁功率跟踪控制思想,使发电机的输出功率跟踪网侧换流器的输出功率,消除了不对称故障情况下直流母线电压的2倍工频纹波和限制直流侧电压上升,避免直流母线电压波动超出电容电压的额定值.1 MW机组的仿真结果表明,所提出的控制策略可实现不对称故障穿越,验证了所提出控制策略的有效性.     

基于超级电容的永磁同步风力发电机不对称故障穿越方法

风电系统与电网之间的相互影响越来越大,需要并网风电机组具有故障穿越能力来保证电网安全运行。为了提高永磁同步风力发电机组(PMSG)在不对称电网故障下的穿越能力,提出了一种基于超级电容储能的PMSG风电机组的故障穿越方法。该方法采用双向直流变换器将超级电容器组连接在交直交变流器的直流母线上,通过对超级电容的吞吐功率进行控制,限制了故障情况下交直交变流器直流侧电压上升,并降低了不对称故障引起的直流母线电压2倍工频纹波。同时在网侧换流器的控制中采用电网负序电压前馈的方法,消除并网电流负序分量。结合低电压穿越标准,对超级电容的容量选取进行了讨论,并建立了超级电容器及其功率变换电路的数学模型,设计了超级电容储能系统的控制器。采用Matlab软件,对1 MW机组的仿真结果表明,所提出的不对称故障穿越方法,可同时减小并网电流负序分量和直流母线电压的2倍工频纹波,提高了机组不对称故障穿越能力,验证了文中提出的故障穿越策略的有效性。     

电网不对称故障下直驱永磁风电机组并网逆变器的双电流闭环控制策略研究

在分析不对称电网电压条件下直驱永磁风力发电机组并网逆变器数学模型的基础上,提出了正负序双电流闲环控制策略,完成风力发电机组在电网发生不对称故障下的不脱网运行.在PSCAD/EMTDC环境下建立基于IGBT背靠背变频器的1.5 MW永磁直驱风力发电系统仿真模型,仿真结果证明该控制策略的可行性.     

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.     

A computer generator for randomly layered structures

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

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。     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

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     

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

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An on-line scaling method for improving scalability of a database cluster

The explosive growth of the Internet and database applications has driven database to be more scalable and available, and able to support on-line scaling without interrupting service. To support more client's queries without downtime and degrading the response time, more nodes have to be scaled up while the database is running. This paper presents the overview of scalable and available database that satisfies the above characteristics. And we propose a novel on-line scaling method. Our method improves the existing on-line scaling method for fast response time and higher throughputs. Our proposed method reduces unnecessary network use, i.e. , we decrease the number of data copy by reusing the backup data. Also, our on-line scaling operation can be processed parallel by selecting adequate nodes as new node. Our performance study shows that our method results in significant reduction in data copy time.     

An improved R-tree based on childnode''s probability

R-Tree is a good structure for spatial searching. But in this indexing structure,either the sequence of nodes in the same level or sequence of traveling these nodes when queries are made is random. Since the possibility that the object appears in different MBR which have the same parents node is different, if we make the subnode who has the most possibility be traveled first, the time cost will be decreased in most of the cases. In some case, the possibility of a point belong to a rectangle will shows direct proportion with the size of the rectangle. But this conclusion is based on an assumption that the objects are symmetrically distributing in the area and this assumption is not always coming into existence. Now we found a more direct parameter to scale the possibility and made a little change on the structure of R-tree, to increase the possibility of founding the satisfying answer in the front sub trees. We names this structure probability based arranged R-tree (PBAR-tree).     

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.     

Integrating GIS Web services based on mediating architecture

The geographic information service is enabled by the advancements in general Web service technology and the focused efforts of the OGC in defining XML-based Web GIS service. Based on these models, this paper addresses the issue of services chaining,the process of combining or pipelining results from several interoperable GIS Web Services to create a customized solution. This paper presents a mediated chaining architecture in which a specific service takes responsibility for performing the process that describes a service chain. We designed the Spatial Information Process Language (SIPL) for dynamic modeling and describing the service chain, also a prototype of the Spatial Information Process Execution Engine (SIPEE) is implemented for executing processes written in SIPL. Discussion of measures to improve the functionality and performance of such system will be included.