基于改进k-means算法的科研仪器机时智能计算系统

传统的机时统计常使用人工,不仅效率低,而且成本相对较大,因此在传统的机时计算的基础上提出一种基于改进k均值聚类算法的科研仪器机时智能计算系统。通过对仪器机时电流数据的聚类分析,完成对仪器机时的计算和统计,同时将传统k均值聚类算法进行改进,提升其系统机时计算的准确性。结果表明,使用改进k均值聚类算法后的机时系统在仪器的机时计算中表现更为优异,计算的时间与正常运行时间相同,能够在一定程度上达到0误差标准。由此可见,使用改进聚类算法进行仪器的机时统计能够提升机时计算结果的准确性。

基于并行k-means聚类的配电网台区无功补偿模块化控制方法

配电网台区无功补偿过程中受到配电线损谐波影响,出现电流、电压不平衡而无法抑制无功电流、电压的问题。为了实现配电网台区无功补偿,结合并行k-means聚类算法提出配电网台区无功补偿模块化控制方法。构建模块化多电平换流器稳定无功补偿控制结构,结合k-means聚类算法归一化计算配电网线损率,避免无功补偿谐波增大而导致电压不平衡,有助于保持无功补偿控制稳定性。采用k-means聚类算法对多个样本分类处理,并将中心样本数据作为聚类中心。结合配电网运行状态,计算电流平衡度,筛选出最佳状态下智能电流控制开关分布状态,改变电流输入和输出的选相,控制无功补偿电流值,保持配电网内部的电流平衡。构建电压正、负序分量变换矩阵,控制目标有功、无功电压。通过引入非闭环控制结构,对实际运行过程中出现的扰动及时纠正,使电压在额定电压调节范围内稳定波动,保持配电网内部电压平衡。由实验结果可知,该方法补偿后无功电流、电压为0,配电网台区主要为有功电流、电压,说明使用该方法能够瞬时抑制无功电流,达到理想补偿效果。

Vertical structure of tidal currents in the Xuliujing Section of Changjiang River Estuary

Three long-term fixed acoustic Doppler current profilers were first used for investigating the vertical structure of tidal currents in Xuliujing Section of Changjiang River Estuary.Moreover,three different periods(spring,summer and fall)were also considered for investigating seasonal variations.The semi-diurnal tides were the most energetic,with along-channel speed of up to 80 cm/s for M_(2)constituent,which dominates at all stations with percent energy up to 65%–75%during seasons.The shape of tidal ellipses of the most energetic semi-diurnal constituent M_(2)showed obvious polarization of the flow paralleling to the riverbank,with the minor semi-axis being generally less than 20%of the major one.The maximum velocity of mean current is appeared in top layers at all the three stations,and the velocity decreased with the depth.The seasonal variations of direction are also observed,which is probably caused by complex local topography since the erosion and deposition in riverbed.Observed vertical variation of four parameters of M_(2)ellipses,agreed well with the optimally fit frictional solutions in top and middle layers.However,there was an obvious difference between frictional model and observed data in the lower water column.Discrepancies are probably on account of stratification,which strengthens in summer and fall due to the freshening influence of the Changjiang River Estuary outflow.

Observed characteristics of tidal currents and mean flow in the northern Yellow Sea

Several bottom-mounted Acoustic Doppler Current Profiler (ADCP) moorings were deployed in the northern Yellow Sea (NYS) during the four seasons of 2006–2007 and also the summertime of 2009. A synthesis analysis on the time-continuous records was performed to examine the characteristics and variations of tidal currents and mean flow over the observation period at these stations. Tidal currents accounted for ~75% of the total kinetic energy, with the absolute dominance of M2 constituent. Visible vertical variations of tidal flow were found on all sites, featured by the decrease of amplitude, increase of rotation rate as well as a decreasing trend of the phase for M2 component with depth. A notable exception was in the central NYS, where the maximum tidal currents occurred in the upper or middle layers (~20–40 m) instead of near the surface (<10 m). The observed mean flow was relatively weak, smaller than 15 cm/s. Velocity on the northern end of Yellow Sea Trough (YST) was characterized by low magnitude and an obvious layered structure vertically. In the Bohai Strait (BS) and the northern slope area, the currents weakened and the flow direction presented a major trend to deflect counterclockwise with depth in most observations. Summertime cyclonic circulation around the Yellow Sea Cold Water Mass (YSCWM), its intensification on the frontal zone and the Yellow Sea Warm Current (YSWC) for the winter season were all evident by our direct current measurements. However, the details of water exchange through the BS appeared partly diff erent from the traditionally-accepted pattern. The vertical diff erences of tidal and mean flow were larger in summer than that in winter, implying the influence of thermal structure to the local currents. Aff ected by the water stratification, mean flow usually reached its maximum near the thermocline in spring and summer, while showing a nearly uniform vertical distribution during winter.

EXISTENCE OF AREA MINIMIZING TANGENT CONES OF INTEGRAL CURRENTS WITH PRESCRIBED MEAN CURVATURE

Given an integral M-currrent To in Rm+k and a tensor H of type(m.l)on Rn+k with values orthogonal to each of its arguments we proved in a previous peper[3]the sxistence of anintegral m-current T =γ(M,θ.ζ)with boundary T0 and mean curvature vector H by minimizing an appropriate functional on suitable subclasses of the set of all integral currents.In thes paperwe discuss the existence and structure of oriented tangent cones C of T at points x∈spt(T) spt(T),especially we show that C is locally mass minimizing.

Fault Identification of Power Grid Based on Wide-Area Differential Current and K-Means Clustering

A new method of fault domain identification is proposed based on K-means clustering analysis theories using the wide-area information of power grid. In the method, the node Intelligent Electronic Device (IED) associated domain is defined, and the relationship of positive sequence current fault component for the association domain boundaries is sought, then the conception of positive sequence fault component differential current for node IED association domains is introduced. The information of the positive sequence fault component differential current gathered by node IEDs is selected as the object of K-means clustering. The node IEDs of fault associated domains can be classified into one category, and the node IEDs of non-fault associated domains are classified into another category. With the fault area minimum principle, the group of node IEDs about fault associated domains can be obtained. The overlap of fault associated domains for different nodes is the fault area. A large number of simulations show that the algorithm proposed can identify fault domains with high accuracy and no influence by the operating mode of the system and topological changes.

Generalized Mean-Flow Theory of Wave-Current-BottomInteractions

The interaction between waves, currents and bottoms in estuarine and coastal regions is ubiquitious, in particular the dynamic mechanism of waves on large-scale slowly varying currents. The wave action concept may be extended and applicated to the study of the mechanism. Considering the effects of moving bottoms and starting from the Navier-Stokes equation of motion of a vinous fluid including the Coriolis force, a generalized mean-flow medel theory for the nearshore region, that is, a set of mean-flow equations and their generalized wave action equation involving the three new kinds of actions termed respectively as the current wave action, the bottom wave action and the dissipative wave action which can be applied to arbitrary depth over moving bottoms and ambient currents with a typical vertical structure, is developed by vertical integration and time-averaglng over a wave peried, thus extending the classical concept, wave action, from the ideal averaged flow conservative system to the real averaged flow dissipative dynamical system, and having a large range of application.

基于谐振变换器的串联储能单元均压控制策略

储能系统中通常通过串联多个储能单体得到更高的电压,但由于每个储能单体电压的不一致性会降低储能单元的利用率。针对以上问题,提出一种基于谐振变换器的串联储能单元均压控制策略。该均衡电路通过开关阵列与谐振变换器相互配合,实现任意单体之间和任意多单体之间的能量传递,且这两种能量传递模式均实现了零电流开关,减少了电路损耗。为获得最优均衡速度和均衡效率,采用K-Means聚类复合控制策略,优先对分组单元进行均衡,然后再进行单体间的均衡。最后,在Matlab/Simulink平台上对6个串联储能单体进行均衡仿真实验,实验结果表明,在静置均衡实验下,电压在24 min左右达到均衡,且均衡精度达到5 mV,均衡效率达到98.98%。与传统均压方法相比,该方法具有更快的均衡速度和更高的均衡效率。

适用于新型配电网的改进型电流保护

随着新型配电网的发展,分布式电源(distributed generation, DG)广泛接入配电网,由于DG运行状态多样随机,传统基于最大、最小运行方式整定的电流保护难以同时满足保护“四性”。为此,本文首先搭建具有低电压穿越能力的多类型高比例DG接入的新型配电网模型,分析多类型DG接入后配网短路计算方法,研究DG接入对电流保护“四性”的影响;提出的改进方案将配网运行状态聚类为多个运行状态集,集内分别整定,当配网运行状态满足定值切换判据时更新定值,形成适用于新型配电网的“离线整定、在线更新”的改进电流保护,最后利用PSCAD/EMTDC仿真验证所提方法的有效性。

The fundamental characteristics of current in the Bering Strait and the Chukchi Sea from July to September 2003

The characteristics of current in the Bering Strait and the Chukchi Sea areanalyzed based on the two current data on the mooring stations during the Second National ArcticResearch Expedition of China in 2003. The tidal currents of the principal diurnal and semidiurnalellipses rotate clockwise in the upper layer, except for N_2, S_2, and Q_1 at Sta. ST. In the BeringStrait (Sta. ST), the major semi-axis of tidal current constituent M_2 is 2.9 cm/s in the upperlayer, which is much smaller than that of semi-monthly oscillation (11.8 cm/s); and the mean currentflows northwestward at the amplitude of about 20 cm/s and varies a little with depth. During thecruise, the current has significant semi-monthly oscillation at the two mooring stations. Thespectra analyses of the air pressure gradient and the wind stress show that there are thesemi-monthly oscillations in these two data series. The near-inertial current, approximately 4 cm/s,presents almost the same magnitude of the principal tidal currents in the Bering Strait.

基于K-means聚类法的牵引供电隔离开关故障状态监测

接触网隔离开关的运行可靠性对于保障牵引供电系统稳定运行有着重要意义。针对隔离开关的机械状态特性,对电机电流与其输出扭矩之间的关系进行了推导。通过电机电流采集系统监测得到隔离开关电机电流信号,使用wolf算法计算得电机电流信号的最大李雅普诺夫指数值为正,证实了该电流信号具有混沌特性。根据相空间重构理论重构电流信号,对重构信号进行K-means聚类分析,获取簇中心并通过簇中心的位置变化判断隔离开关的故障情况。据此将隔离开关的故障情况进行分类,为隔离开关运行的故障监测以及状态评估提供依据。

基于多维波形差异度聚类分析的配电网故障区段定位方法

谐振接地系统运行环境繁杂,单相接地故障发生状态多变,基于单一特征量的传统配电网故障区段定位方法存在各自的定位判别盲区,方法可靠性和适用性难以保障。针对上述问题提出了一种无需整定的基于多维波形差异度聚类分析的配电网故障区段定位方法。依据故障点上下游各检测点零序电流暂态及稳态分量的波形差异性特征,通过离散Fréchet距离算法量化相邻检测点间的暂态及稳态波形差异度,并采用模糊C均值算法(fuzzyC-means,FCM)综合多特征信息以区分正常区段与故障区段,有效消除了单一特征定位盲区,实现故障区段自适应准确定位。PSCAD/EMTDC仿真结果以及10kV真型实验结果表明所提方法不仅保证了在不同故障工况下的定位可靠性和适用性,还具有耐高阻能力强、抗噪性高等优点。

基于频域分析的DAB变换器优化控制策略

为提高双有源桥(DAB)变换器的工作效率,简化DAB变换器的分析过程,此处在频域分析下采用矢量分析方法,提出了一种最小均方根电流的控制策略。相比于时域分析下通过详细的模式分析过程以及复杂的数学优化工具得出的优化控制策略,频域分析方法无需求解开关周期中各时段的状态方程,通过矢量图直观地推导出以电流有效值为优化目标的控制策略。在约束范围内,该策略可以有效降低电流有效值,提高传输效率。最后,通过搭建实验平台,验证了所提优化控制策略的有效性。

电商企业业财一体化建设现状及改进措施探析

新的市场经济条件下,电商企业对现代信息技术手段的灵活运用,以及业财一体化建设工作的推进程度,对实现财务管理转型升级具有重要现实意义。文章以此为切入点,对电商企业业财一体化建设的重要性进行阐述,依据实际对其现存问题进行分析探讨,并结合自身思考提出改进的建议措施,旨在帮助电商企业找到提升业财一体化建设路径,为长远发展充能蓄力。

基于在线特征库的非侵入式负荷特征提取方法

负荷特征是指负荷设备运行过程中具备某种统计规律的特殊标识,而包含负荷特征的数据库则是实现非侵入式负荷监测与分解的基本依据。对于纯阻性负荷设备,研究人员利用其运行状态切换过程中功率产生跃变的特点,可以准确提取相应状态下的负荷特征。然而,对非纯阻性设备,其负荷特征提取存在以下2个问题。问题1)运行状态切换过程中功率变化不显著,无法精准定位状态投切时刻点;问题2)负荷设备存在功率缓变化的运行状态,导致对应状态下的负荷特征不唯一,无法手动提取。为了解决非纯阻性设备负荷特征提取中存在的上述问题,提出一种基于在线特征库的非侵入式负荷特征提取方法,该方法分为2个阶段。第一阶段:基于负荷设备运行过程中的稳态周期电流数组建立在线特征库,通过改进Pearson相似系数构建滑窗函数,得到负荷设备运行时的周期电流数组与在线特征库的相似性,并同步判断在线特征库冗余性,实现负荷设备状态数据分割;第二阶段:计算在线特征库的特征矩阵,对特征矩阵进行K-means聚类分析,融合相似在线特征库,形成负荷设备的状态特征库,从而实现负荷设备特征电流数组的提取。在私人数据集和PLAID数据集上的测试结果证明,所提负荷特征提取方法在不同的用电场景下均有较好的鲁棒性。所提方法可大幅减少负荷特征提取阶段的人工参与,有利于缓解因负荷设备种类过多导致的负荷特征提取烦琐的问题,为后续建立负荷特征数据库提供了便利。

基于K-means和SOM混合算法的高压断路器操作机构状态评估

为诊断高压断路器操作机构故障,文中基于分合闸线圈电流曲线,提出了采用K-means与SOM神经网络相结合的混合算法,对断路器操作机构进行状态评估。对某批次252 k V高压断路器操作机构进行分合闸线圈电流数据采集;建立了K-means与SOM神经网络相结合的混合算法模型;对测试的断路器操作机构进行状态分析。结果表明,混合算法能够将操作机构不同状态进行聚类,可将相同故障分在同一类别。并将混合算法模型与SOM神经网络模型和K-means模型作比较,结果表明,混合算法模型在计算速度和聚类准确率上都优于其他两种模型。

基于双主动全桥双向DC/DC变换器的混合单移相调制方案

对双主动全桥DAB(dual active bridge)双向DC/DC变换器的调制方案进行了研究,DAB变换器的主要优势在于具有对称结构、双向潮流能力、宽软开关区域和灵活的控制能力等特点。控制这种拓扑结构最简单的方法是通过控制变换器原副边全桥之间的移相角来控制功率传输的方向和大小。然而在轻载条件下,当变换器的输入或输出电压变化较大时,会产生大量的无功功率,同时部分开关管的零电压开关ZVS(zero voltage switching)操作会丢失而直接导致转换效率变低。因此,为了提高DAB变换器的效率,提出了一种混合单移相调制PSM(phase shift modulation)方案,在保持控制简单的基础上,通过减小电感电流有效值,扩大软开关的范围,提高了变换器的效率。首先,通过让拓展移相EPS(extended phase shift)、双移相DPS(dual phase shift)以及三移相TPS(triple phase shift)调制方案中的可控变量相等,从而形成了4种不同的PSM方案。接着,对这些调制方案进行了稳态特征的比较分析,包括传输功率容量、电感电流水平以及软开关性能等。在此基础上,提出了一种混合PSM方案。最后,通过搭建实验平台验证了所提出调制方案的有效性和正确性。

中华优秀传统文化融入大学生思想政治教育路径探索

中国传统文化源远流长,优秀传统文化更是当代经济社会发展的宝贵财富。新时代发展中,传统文化的重要性日益凸显,重视优秀传统文化的传承,是不断促进民族进步、提升民族凝聚力的根脉所在。将中华优秀传统文化融入大学生思想政治教育中,有利于帮助大学生树立正确的价值观念;有利于继承弘扬传统文化精神;有利于为社会培养思想政治水平高的优秀人才,能有效提升广大学生优秀传统文化涵养,拓宽大学生德育思维。该文通过调研走访、翻阅资料得知当前部分高校传统文化与思想政治教育融合形态,旨在为二者的教育融合提出些许参考建议,以期强化传统文化的现实教育意义,进一步弘扬优秀传统文化精神,促进传统文化与大学生思想政治教育的有机结合。

卫星重力场模型在海洋环流分析中的应用

本文选用GOCE、GRACE和DGM 3种地球重力场模型,以及卫星测高获取的平均海面高模型,计算了4个模型下的地转流并进行对比,结果表明:用GOCE重力场模型比用GRACE重力场模型计算的地转流中长波精度有一定提高,能展现出尺度更小、细节更丰富的地转流;利用移去恢复法可使全球稳态海面动力地形(MDT)的高频信息得到有效恢复,可显著提升地转流的细节特征。

弗兰克-赫兹实验理论曲线推导

弗兰克-赫兹实验中的板极电流的理论预测模型亟待建立,现有相关理论工作侧重于对实验结果的分析和阐释,而少数理论计算模拟的工作或未展现理论曲线全貌,或运算耗时较长.本文基于两条引理和三条假设,将解析与编程结合,在1秒内给出理论曲线全貌,并分析其与实验值偏差的原因,据此引入电子运动轨迹和通过率修正,给出修正曲线全局预测,其与实验结果的符合度较高.这不但检验了玻尔理论的正确性,也表明理论成果可用于一定范围内板极电流的预测.