Three-phase rectifiers that apply optimal current injection

A class of current injection based three-phase high power factor rectifiers is proposed. Low distortion of the input currents and high power factor are obtained applying near optimal current injection. The optimal current injection is discussed, and requirements it imposes to the current injection network are derived. A class of simple current injection networks that provide near optimal current injection, consisting of a transformer, two capacitors, and a number of resistors or resistance emulators is proposed. The power processed by the resistors or resistance emulators is shown to be 8.81% of the input power. Design of the current injection network is discussed, and dependence of the input current distortion on capacitance of the applied capacitors is analyzed. Volt-ampere rating of the transformer is shown to be only 0.16% of the input power. Effects caused by the output current ripple are studied, and a method for their compensation is proposed. Analytical results are experimentally verified. Switching resistance emulation is discussed and its feasibility is experimentally demonstrated     

Low-harmonic three-phase inverters with nonpulsating terminalcurrents

A basic class of three-phase inverters with nonpulsating terminal currents, namely, the four-topology four-inductor four-capacitor class is derived and studied. The expressions of duty-ratios required for low-harmonic dc-to-three-phase-ac conversion, ranges of output voltage variation, and component stresses for given specifications of inverters are derived. The characteristics of inverters include low-harmonic power conversion, low component stresses, variable-frequency variable-amplitude output voltages of values both below and above the dc input value, and the use of minimum number of inductors to achieve nonpulsating terminal currents     

Cholesky分解的应用研究

Cholesky分解是应用广义最小二乘法的关键，主要是根据所得资料信息，得到一正定对称矩阵，这正是所有有意用广义最小二乘法解决的问题难以满足的，我们解决的方法是求一较低阶正定对称矩阵，进行Cholesky分解，从而将广义最小二乘法应用于分析研究经Durbin-Watson检验是相关的残差序列。     

多媒体技术应用于英语教学的和谐性问题

本认为，多媒体技术正越来越深刻地影响着英语教学，它能创造虚拟的情境，提高课堂教学的密度，提供个别化的学习环境，从而提高英语教学的趣味性和教学效率。本还认为，在应用多媒体技术在英语教学中时，应注意保持教学诸要素之间的和谐关系，即教师、学生、教材、方法相互之间的和谐，正确的把握多媒体使用的度，同时，要加强理论的学习，才能最大限度地发挥多媒体技术的作用。     

智能压力变送器多种应用方式的探讨

压力、差压变送器是过程变量变送器中最重要的一类,随着生产过程自动化程度的不断提高,在生产过程控制领域得到越来越广泛的应用,除了可用于压力、差压测量之外,还可用于流量、液位、比重等其他参数测量,以差压原理的流量测量技术更是在流量测量领域占有绝对的高的比例.差压变送器在各种应用领域中的安装及设置方法也多种多样,针对其在这些测量领域的测量方法及原理进行分类的阐述.     

基于基波电流观测器和旋转高频电压注入法的IPMSM无传感器控制

为了实现永磁同步电机低速段的高精度无传感器运行,系统地分析了绕组电阻和感应电动势、电流调节器、滤波器、电机暂态运行、注入高频电压的幅值与频率、多凸极效应、电流传感器精度以及A/D采样量化误差等因素对基于旋转高频电压注入法的低速无传感器控制方法转子位置估计精度的影响机理。在此基础上,提出了一种基于基波电流观测器和旋转高频电压注入法相结合的低速无传感器控制策略,消除了传统的无传感器控制方法中带通滤波器引起的转子位置估计误差,并降低了电机暂态运行引起的转子位置估计误差,有效地提高了低速无传感器控制方法的转子位置估计精度。仿真和实验结果表明,所提出的低速无传感器控制策略具有更高的转子位置估计精度和更宽的调速范围。     

On applying the extended Kalman filter to nonlinear regressionmodels

In using an extended Kalman filter to estimate the parameters of a nonlinear regression model, the order in which the measurements are processed can be important, as the filter cannot always be expected to produce a satisfactory global fit when processing the measurements in the causal order in which they occur. To obtain a better fit, the possibility is explored of using a sequential state estimator in an offline mode to process the measurements in a random order rather than in the causal order in which they occur     

Aero-engine fault diagnosis applying new fast support vector algorithm

A new fast learning algorithm was presented to solve the large-scale support vector machine ( SVM ) training problem of aero-engine fault diagnosis.The relative boundary vectors ( RBVs ) instead of all the original training samples were used for the training of the binary SVM fault classifiers.This pruning strategy decreased the number of final training sample significantly and can keep classification accuracy almost invariable.Accordingly , the training time was shortened to 1 / 20compared with basic SVM classifier.Meanwhile , owing to the reduction of support vector number , the classification time was also reduced.When sample aliasing existed , the aliasing sample points which were not of the same class were eliminated before the relative boundary vectors were computed.Besides , the samples near the relative boundary vectors were selected for SVM training in order to prevent the loss of some key sample points resulted from aliasing.This can improve classification accuracy effectively.A simulation example to classify 5classes of combination fault of aero-engine gas path components was finished and the total fault classification accuracy reached 96.1%.Simulation results show that this fast learning algorithm is effective , reliable and easy to be implemented for engineering application.     

ATE系统在飞机定检中的应用研究

介绍了ATE系统的工作原理及其在飞机定期检测中的应用;针对工作中遇到的问题提出了解决方法和一些设想.     

超临界喷射受环境和喷射参数影响的数值研究

基于PR(Peng-Robinson)状态方程,采用二维轴对称的两相流控制方程和相关文献中的混合规则,建立了超临界燃油喷射的数值模型并采用预处理方法进行求解.以正癸烷为替代燃料研究了超临界燃油喷射到静止超临界氮气环境中时射流长度和射流扩张角的变化规律.结果表明:超临界射流长度和射流扩张角随环境压力的升高而减小,随环境温度和喷射温度的升高而增加,且超临界射流长度受环境和喷射参数影响的敏感性稍高于射流扩张角.分析认为影响超临界喷射的两个主要因素是喷射密度比和喷射动量,且后者占主导地位.     

The storm-time ring current

In this paper I am reviewing recent advances and open disputes in the study of the terrestrial ring current, with emphasis on its storm-time dynamics. The ring current is carried by energetic charged particles flowing toroidally around the Earth, and creating a ring of westward electric current, centered at the equatorial plane and extending from geocentric distances of about 2 R _E to roughly 9 R _E. This current has a permanent existence due to the natural properties of charged particles in the geospace environment, yet its intensity is variable. It becomes more intense during global electromagnetic disturbances in the near-Earth space, which are known as space (or magnetic or geomagnetic) storms. Changes in this current are responsible for global decreases in the Earth's surface magnetic field, which is the defining feature of geomagnetic storms. The ring current is a critical element in understanding the onset and development of space weather disturbances in geospace. Ring current physics has long been driven by several paradigms, similarly to other disciplines of space physics: the solar origin paradigm, the substorm-driver paradigm, the large-scale symmetry paradigm, the charge-exchange decay paradigm. The paper addresses these paradigms through older and recent important investigations.     

边界扫描测试技术在集成电路测试中的应用

边界扫描技术是一种新型的VLSI电路测试及可测性设计方法,它提供了对电路板上元件的功能、互连及相互间影响进行测试的一种新方案。介绍了边界扫描技术的原理、结构,讨论了该技术在集成电路测试中的应用。     

一种适用于三维混合网格的GMRES加速收敛新方法

为提高流场计算收敛效率,发展了一套适用于三维混合网格Naiver-Stokes方程求解的并行广义最小残差（GMRES）隐式时间推进方法。该方法由科学计算可移植扩展工具包（PETSc）中的Krylov子空间求解器实现,线性方程系统中的系数矩阵直接以显式给出以提高算法的稳定性。为进一步提高GMRES方法的收敛速度,对非结构网格的序号进行了重排序,使得系数矩阵的非零元素尽量向主对角线靠近。利用所发展的GMRES方法,完成了对ONERA-M6机翼、AIAA阻力预测会议通用研究模型（CRM）等算例的计算,计算结果与试验结果吻合良好。通过与其他隐式推进方法进行比较,对算法的收敛特性进行了研究。结果表明,所发展的GMRES方法计算更加稳定,残差下降速度相对LU-SGS（Lower-Upper Symmetric Gauss-Seidel）方法更快,尤其是气动力系数向着收敛解逼近的速度更加明显,提高了计算效率。     

Improved creep aging response in Al-Cu alloy by applying pre-aging before pre-straining

The improvement of post-form properties without compromising creep formability has been a critical issue in creep age forming of aluminum alloy component. A pretreatment process incorporating artificial pre-aging at 165 °C for 6 h/12 h/24 h followed by pre-strain(3%–9%)has been developed. This method not only evidently improves the strength but also accelerates the creep deformation during creep aging of an Al-Cu alloy. A strength increase of 50 MPa with a slight decrease of ductility relative t...     

四极透镜电流对CT法测束流发射度的影响

利用CT法测量束流发射度是近年来出现的高能强流速束流发射度高精度测量诊断技术。主要就四极透镜电流变化带来的角度分布不同对束流发射度重建精度的影响进行了研究,选取了系列不同的重建角度分布进行模拟计算。研究结果表明,不同的角度分布对重建精度有很大影响,当角度均匀取值时,重建精度最佳。     

Nanoflares and current sheet dissipation

Energy must be continually supplied to the solar corona to maintain both its average temperature and its high energy manifestations. The energy is supplied by photospheric motions and the magnetic field acts both to transmit this energy to the corona and as the furnace in which the energy is stored. The means by which the energy is dissipated and transformed into the actual forms we observe is the activation of current sheets. We conjecture here the properties of such current sheets as derived by both energetical arguments and numerical evidence of the self-organization of a system of currents in a highly turbulent medium. The consequences of the appearance of spatial and temporal intermittency on the different aspects of solar acitvity are also discussed.     

STARSEM current and future activity

The launch services industry is facing a tremendous evolution caused by the changes brought to the design of the satellites. The launch industry must cope with the ‘smaller, faster, better’ era. This context was the main reason for the creation of the European-Russian joint venture STARSEM, promoting exclusive marketing of SOYUZ launch services.     

关节轴承的三向加载技术研究

主要研究关节轴承三个方向加载的耐久性试验技术,制订了试验方法,自主研制了一套专用试验装置.在相同试验条件下,通过两家公司具有相同技术要求的关节轴承耐久性试验验证了试验方法和试验装置;测量了试验件的轴向和侧向间隙,获得了试验件的磨损特性.     

自激励式电磁铆接放电电流分析

电磁铆接是一种将电磁能转化为机械能的铆接工艺。传统感应式低电压电磁铆接存在能量利用率低、难以解决高强度大直径铆钉和难成形材料铆钉的铆接等问题。基于自激励式电磁铆接技术,建立放电电流分析模型,通过数值分析与工艺试验探讨自激励式电磁铆接进行大直径铆钉成形的可行性。研究结果表明建立的电磁铆接放电电流分析模型可实现传统感应式和自激励式电磁铆接放电电流分析,分析结果与试验吻合较好;放电能量相同时,自激励式电磁铆接的涡流斥力峰值要远大于感应式的涡流斥力,能有效提高能量利用率,是实现大直径铆钉成形的有效方式;在放电电压为320V时,自激励式电磁铆接可实现直径为10mm的45号钢铆钉的成形,其变形以绝热剪切的方式进行。     

Self-organization in a current sheet model

Self-organization is a possible solution to the seemingly contradicting observation of the repeatable and coherent substorm phenomena with underlying complex behavior in the plasma sheet. Self-organization, through spatio-temporal chaos, emerges naturally in a plasma physics model with sporadic dissipation. This revised version was published online in August 2006 with corrections to the Cover Date.