级联型多电平逆变器的空间矢量控制

针对级联型多电平逆变器,提出了一种高性能的空间矢量控制方法。这种方法基于空间矢量理论确定与参考电压矢量误差最小的电压矢量,它能够在接近基频的开关频率下输出接近正弦波的电压。仿真结果证实了空间矢量控制所具有的一系列显著优点。     

阵列光束在湍流大气中传输的光强闪烁研究进展

相比单束光,阵列光束由于各光束之间互不相干,可以减小大气湍流引起的接收光强起伏。特别在激光照明和通信等应用场合中,非相干合成光束可以明显提高照明均匀性和减小通信误码率。简要介绍了相干合成阵列光束在湍流大气中传输的光强闪烁研究进展。针对非相干合成阵列光束在减小光强闪烁的优势,回顾了非相干合成阵列光束在激光主动照明、星地激光大气通信方面的实验研究结果;详细总结了子光束为不同类型的非相干合成阵列光束的理论研究方法和结果,包括不同波长光、基模高斯光、部分相干高斯光和艾里光。实际中子光束一般为部分相干光,它们互相之间存在相干性。提出了下一步应深入开展研究的问题为阵列光束大气的光强闪烁。     

单芯大截面电缆施工设计剖析

通过一个变电所工程投运后，电缆间产生较大的感应电流，造成不能正常供电运行，论述如何从理论和实践方面分析原因，采取措施，消除不正常现象。同时，也指出单芯大截面电缆施工设计中应注意的事项。     

The effects of wall roughness on the methane flow in nano-channels using non-equilibrium multiscale molecular dynamics simulation

This paper presents a non-equilibrium multiscale molecular dynamics simulation method to investigate the effects of periodic wall surface roughness on the structure and mass transfer of methane fluid through the silicon nano-channels. In order to accurately capture the trajectories and microstructure of methane nano-fluidics, the present modification of OPLS fully atomic model is employed. Meanwhile, we introduce the corresponding coarse-grained model to solve the problem of wall–fluid interaction for methane Poiseuille flow within silicon atomic walls using the classical Lorentz–Berthelot mixing rules. The geometries of the upper wall roughness are modeled by rectangular waves with different amplitudes and wavelengths. The three-dimensional number densities of C (H) atom and kinetic energy distribution plots give a clear observation of the impacts of surface roughness on the localization micro-information of methane fluid. Moreover, the slip length of fluid over rough surface decreases with the increase in amplitude. The diffusion coefficients appear anisotropic, and the radial distribution functions decrease with the increase in the amplitude. These properties should be taken into account in the design of energy-saving emission reduction nano-fluidic devices. All numerical results also indicate that the presented method not only can well solve the issue of wall–fluid interactions, but also could accurately predict the micro-information and dynamic properties of methane Poiseuille flow.     

SVPWM控制三电平逆变器

论述了空间电压矢量调制（SVPWM）控制二极管钳位式三电平逆变器的原理与实现方法。提出了确定参考矢量的三个规则，并推导出工作矢量作用时间、输出顺序及描述了中点电位的控制规则。通过采用Matlab仿真，结果证明SVPWM控制三电平逆变器的可行性。     

Studying the viscosity of methane fluid for different resolution levels models using Poiseuille flow in a nano-channel

In this work, the viscosity–temperature–density relationship of methane is investigated for three fully atomistic models (RISM, OPLS and MOPLS) and the corresponding coarse-grained models (CGRISM, CGOPLS and CGMOPLS) by studying the Poiseuille flow inside a silicon nano-channel using molecular dynamic simulation. In order to solve the interaction problem of nano-channel atom and methane molecule, the coarse-grained methane model and the classical Berthelot–Lorentz mixing rules are employed. The optimized coarse-grained methane models are determined using the relative entropy minimization method. The density distribution, stress force profile and velocity profile of coarse-grained models are compared with the fully atomistic models for different nano-channel widths. It is concluded that the results of coarse-grained model are in reasonable agreement with those of the corresponding fully atomistic model. Furthermore, the value of viscosity is calculated by fitting the velocity profile to the continuum solution from the Navier–Stokes equations and then compared to experimental value. The results show that the MOPLS and CGMOPLS models could well predict the viscosity of methane fluid, while the OPLS model performed worst. All simulation results indicate that the coarse-grained models can be used to predict the viscosity of methane fluid accurately.     

基于人事事件迭代的电网企业人力资源配置预测模犁研究

随着电网规模不断扩大,企业用工总量逐年减少,结构性缺员问题逐渐由量变转为质变,因此实现企业用工的精确预测和科学配置变得尤为重要.结合电网企业用工特点,利用现有人力资源大数据,提出了一种基于人事事件迭代的预测模型,实现对电网企业未来几年人力资源配置情况的系统性精确预测.     

深基坑墙顶水平变形的灰色-时序动态预测

深基坑墙顶水平变形是一个动态的相互依存的过程。在基坑开挖与施工过程中 ,根据变形观测数据用灰色系统理论与时间序列分析方法建立等维新息动态预测预报模型 ,并随着新数据的加入适时修改模型参数。该模型不要求考虑复杂的变形影响因素。工程实例研究表明 :用组合模型预测变形值 ,其误差大多数情况下小于 5 % ;在变形数据变化较大时 ,组合模型预测值明显优于单一模型预测值。在变形变化平稳时 ,用单一的灰色模型或灰色时间序列组合模型预测误差相差不大。预测步数越多 ,则预测精度越低。     

被动方桩土拱效应三维有限元分析

基于大型有限元软件包ADINA,建立模拟被动方桩的三维有限元模型,对在桩顶边界条件和桩土接触变化时桩基的不同性状进行分析:包括土拱效应机理,桩土间的成拱效应,桩身挠度与表面荷载的变化规律以及桩侧土压力、桩身轴力的变化规律。分析结果表明,黏性土地基在邻近堆载作用下,桩身挠度与表面荷载呈非线性关系,可以用三折线模型来模拟;桩顶自由时,桩前土压力介于朗肯主动土压力与被动土压力间,呈非线性分布;在同种土中,桩侧极限土压力沿桩身呈线性分布,但比Ito理论和沈珠江理论都小。     

保护东滩湿地爱护绿色家园

湿地是地球上具有高度多样性的独特生态系,它与海洋、森林并列为世界三大生态系。它具有季节或常年积水、生长和栖息喜湿植物、动物和土壤发生熟化3个基本特征。根据1971年2月在伊朗拉姆萨尔签署的《湿地