电容式电压互感器附加相位差对绝缘在线监测的影响

绝缘在线监测系统一般从电压互感器二次侧取参考电压信号,当采用电容式电压互感器(CVT)二次侧电压作为测量基准时,其附加相位差对监测结果的准确度有不可忽略的影响。     

反铁畸变中钛酸锶(SrTiO3)晶体学原胞的选取

通过对钛酸锶（SrTiO3)在相变前后结构对称性的分析，提出了与之相应的两种晶体学原胞的选取方法。无论选取D4和D2d哪一种原胞，其对称元素个数均为8，即对称元素个数保持不变，只是所选原胞体积相差一倍。因此，在选取原胞时必须遵从以下两个原则：1）所选晶体学原胞的体积在相变前后要保持不变；2）所选取的晶体学原胞，应最能反映相变前后晶体结构对称性的变化，且其对称元素个数不因所选原胞体积的不同而变化。     

电压电流双闭环瞬时值控制级联逆变器研究

本文第一部分对单相级联型逆变器的几种PWM调制技术较详细的理论和仿真对比分析，找出它们的内在联系，并从中找出单相级联型逆变器的最佳调制方案。第二部分针对该种调制方案应用电压电流双闭环瞬时值反馈技术制作了一台原理样机，瞬时值控制技术的采用可以加快系统的动态响应和提高非线性负载适应能力。在电流控制环中，用电容电流反馈取代传统的电感电流反馈可以显著提高系统的外特性硬度。仿真和试验验证了电压电流双闭环瞬时值控制级联逆变器具有优良的稳态和动态性能。     

A current‐mode 1kHz/10kHz low‐voltage integrated analogue PLL for lock‐in portable applications

We present a low‐supply voltage (2V) low‐power consumption (500W) analogue phase‐locked loop (PLL), working at two low frequencies (1 and 10kHz), to be used in an integrated lock‐in amplifier. An externally settable control bit allows the switching operation between the two different frequencies. The circuit has been designed in a standard 0.6–m CMOS technology and differs from the standard analogue PLL architectures for the current mode implementation of both the loop filter and of the oscillator. Three different locked waveforms (sinusoidal, triangular, squared) can be obtained at the PLL output. Simulation results, obtained through the use of PSPICE and using accurate transistor models, will be proposed. The pull‐in ranges are about ±250Hz around 1 and ±1.3kHz around 10kHz, with pull‐in times of about 10 and 4ms, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

基于s注入法的小电流系统消谐与选线一体化方案研究

单相接地故障和铁磁谐振故障是小电流系统经常发生的故障。首先介绍了s注入法选线和测距的基本原理 ,然后提出了利用频率检测法和s注入法相结合辨别单相接地故障与铁磁谐振故障的方法 ,有效解决了接地信号发生时将铁磁谐振故障误认为接地故障进行处理的问题 ,由此提出了利用s注入法实现消谐和选线一体化的可行性方案     

MgCu_2型Laves相晶格常数的规律性

根据Miedema的合金元胞模型，用人工神经网络－原子参数方法总结MgCu2型Laves相晶格常数的规律性，从而提出一种计算Laves相晶格常数的方法。     

快速跳频电台频率合成器的研究

跳频通信具有很强的抗干扰能力,是未来战场通信的主要通信手段。跳频速率的快慢很大程度上决定了跳频电台抗干扰能力。实现快速跳频通信的关键之一是要求频率转换时间极短的频率合成器,常规的频率合成技术已难以满足要求。论文介绍一种数字式直接频率合成器加锁相环(DDS PLL)的频率合成器,具有换频时间短、覆盖波段宽、分辨率高等优点,可以满足战场通信用的快速跳频电台的要求。     

已知非最小相位系统的跟踪问题研究

本文探讨了已知离散时间非最小相位系统的跟踪问题，证明了一大类针对非最小相位系统的线性控制器（其具体形式将在文中给出）不能实现对任意有界设定序列的渐近跟踪，这表明对未知离散非最小相位系统，不可能设计Ｃｌａｒｋｅ－Ｇａｗｔｈｒｏｐ型自动校正控制或自有因地制宜制品在去渐近跟踪任意有界设定序列。     

基于电压波形分析的十二相整流装置故障诊断

通过对十二相整流装置正常工作和故障运行时，整流元件电压波形的分析，提出了用以判断整流元件工作状态的特征函数，根据由该函数求出的特征值，可以对十二相整流装置的故障（包括复合故障）进行在线诊断，确定故障性质，并能准确定位到具体元件。     

Measurement of flow in small vessels by magnetic resonance phase mapping techniques: anin vitro andin vivo study

The measurement of blood flow in small arteries is a potential extension of magnetic resonance (MR) angiography. We have compared flow measurements based on MR phase mapping with those obtained by Doppler ultrasound and electromagnetic flowmetry in both phantom and animal models. Correlation between modalities was high forin vitro studies (R ²=0.93–0.98).In vivo, electrocardiogram-gated MR and Doppler ultrasound flow measurements compared to electromagnetic flowmetry showed fair correlation coefficients (R ²=0.73 and 0.66, respectively). However, limits of agreement indicated that in small vessels flow measured by the three modalities could differ by up to ±90 mL/min. For both models, arteries in the range of 3–6.5 mm in diameter produced complementary errors in area and velocity measurements in MR studies. Ungated MR studies showed a reduced agreement (R ²=0.88in vitro, 0.54in vivo), which may in part be due to poor sampling of the velocity pattern. The results show that the high correlation obtainedin vitro cannot be extrapolated to thein vivo situation, where additional physiological and anatomical variables are encountered.