Multi-parameter identification of power line communication channel model based on matching pursuit

The over-complete atom dictionary is designed on the basis of typical multi-path transmission function of power line communication (PLC) channel, and matching pursuit (MP) algorithm is used for multi-parameter identification of the channel. First, the sampling data were obtained from the measured result of low-voltage PLC channel within the range from 300 kHz to 6000 kHz, which help us to develop a model for the PLC channel. Then, in order to reduce the computation complexity of MP algorithm to identify the multi-parameter of PLC, genetic algorithm (GA) is applied to effectively search for the best atom at each step of MP in the dictionary of atoms. From the multi-parameter identification result with three or four paths channel models, it demonstrates that the combined algorithm based on MP and GA can acquire more evaluation precision of PLC channel than that of GA and particle swarm optimization (PSO) algorithm respectively. Meanwhile, the more numbers of channel paths in the process of multi-parameter identification, the better will be the curve fitting result compared to the experiment. The experimental results have validated the efficiency of the combined MP–GA algorithm that proposed in this paper.     

电动斥力作用下低压断路器分断特性的研究

基于多体动力学原理,建立低压塑壳断路器操作机构的仿真模型,并通过试验验证模型的正确性.依据电场、磁场、斥力之间的关系,建立了低压断路器分断过程中电动斥力的数学模型,通过计算不同电流和触头转角下导电回路的洛仑兹力,应用二元三次插值技术分析电动斥力.并且通过ADAMS二次接口的自编程实现了电路方程、电磁场和机构运动方程的耦合求解.结果表明,由于电动斥力的作用,加快了断路器的分断,低压断路器在预期短路电流10kA下,机构的动作时间比空载时缩短了1ms.     

变频器跳闸分析及解决方法

以某35kV专线用户为例,分析了相邻线路故障引起专线用户变频器跳闸的原因,从调整继电保护方式以减少母线电压波动和调整变频器参数以增加其对低压的耐受力两方面出发,深入探讨可能采取的措施,并详细阐述了其原理.     

交流接触器开关电弧的图像采集与处理

综合利用计算机视觉技术、光电子技术、CCD(Charge Coupled Device)高速成像技术和计算机图像处理技术研制了一种集图像采集、传输、存储、处理于一体的新型电弧图像高速采集系统,利用该系统可拍摄到低压电器开关电弧从燃弧到灭弧的一系列图像。为有效地抑制噪声、提高信噪比,本文首先应用自适应中值滤波算法去除随机噪声,然后采用拉普拉斯掩模锐化算法突出图像的边缘和细节,使处理后的电弧运动图像边缘清晰可辨,从而适于对电弧直径变化进行分析计算。通过对处理后的电弧从燃弧到灭弧的一系列图像的分析理解,归纳出低压交流接触器分断电弧的燃弧过程的特点,且发现所得的电弧运动图像特征与电弧的大量仿真结果相一致。     

低压配电系统区域选择性保护的解决方案

区域选择性联锁技术作为一种新的保护方式,克服了传统配电系统保护中上下级间选择性难以配合,短路电流对系统的冲击大等缺点。介绍了区域选择性联锁技术的基本原理,重点阐述了低压配电系统中通用型低压断路器各级之间区域选择性联锁的实际解决方案,从而有效地提高配电系统的安全性和可靠性。     

An improved low-voltage ride-through performance of DFIG based wind plant using stator dynamic composite fault current limiter

In this paper, an enhanced low-voltage ride-through (LVRT) performance of a grid connected doubly fed induction generator (DFIG) has been presented with the usage of stator dynamic composite fault current limiter (SDCFCL). This protection circuit comprises of a suitable series resistor–inductor combination and parallel bidirectional semiconductor switch. The SDCFCL facilitates double benefits such as reduction of rotor induced open circuit voltage due to increased value of stator total inductance and concurrent increase of rotor impedance. Both effects will limit rotor circuit over current and over voltage situation more secured way in comparison to the conventional scheme like the dynamic rotor current limiter (RCL) during any type of fault situation. The proposed concept is validated through the simulation study of the grid integrated 2.0 MW DFIG.     

Recovery characteristics of a YBCO high-temperature superconducting current-limiting element for use in low-voltage distribution systems

Recovery characteristics of a YBa₂Cu₃O_7-y high-temperature superconductor after its quenching are investigated experimentally in this paper. The zigzag-shape superconducting elements 310 mm in effective length and 1.5 mm × 1 mm in cross section are examined. AC current injection tests are carried out. It is clarified that the high-temperature superconducting element has a quick transition characteristic between the super- and normal-conducting states. The test elements recover to zero impedance state from high impedance state just after removing the over-current when the magnitude of accumulated heats due to the over-current during the quenching period is less than 1 J. Furthermore, it is found from experiments that the critical current level might be reduced by some self-magnetization due to a high current during the quenching period.     

基于工控组态软件的低压配电监控系统设计

针对济宁全民健身广场低压配电管理自动化的要求,利用电力工控组态软件,设计一套具有人机交互界面的智能电力监控系统。在智能电力仪表、RS485总线和基于Windows操作系统的PC机构建的平台上,采用专业的EpSynall电力系统自动化组态软件进行二次开发,完成监控系统的设计。低压配电监控系统全程监测各电参量,在有跳闸或其他故障时报警,工作人员及时发现并排除故障进而确保供电正常,实现对低压配电的自动化管理。     

Transmission electron microscopy at 20 kV for imaging and spectroscopy

The electron optical performance of a transmission electron microscope (TEM) is characterized for direct spatial imaging and spectroscopy using electrons with energies as low as 20 keV. The highly stable instrument is equipped with an electrostatic monochromator and a C_S-corrector. At 20 kV it shows high image contrast even for single-layer graphene with a lattice transfer of 213 pm (tilted illumination). For 4 nm thick Si, the 200 reflections (271.5 pm) were directly transferred (axial illumination). We show at 20 kV that radiation-sensitive fullerenes (C₆₀) within a carbon nanotube container withstand an about two orders of magnitude higher electron dose than at 80 kV. In spectroscopy mode, the monochromated low-energy electron beam enables the acquisition of EELS spectra up to very high energy losses with exceptionally low background noise. Using Si and Ge, we show that 20 kV TEM allows the determination of dielectric properties and narrow band gaps, which were not accessible by TEM so far. These very first results demonstrate that low kV TEM is an exciting new tool for determination of structural and electronic properties of different types of nano-materials.     

A new family of CMOS inverter-based OTAs for biomedical and healthcare applications

This paper presents a new family of innovative operational transconductance amplifier (OTA) topologies based on CMOS inverter structures, with improved gain and energy-efficiency. This new family of OTA designs is suitable for biomedical and healthcare circuits and systems, due to the high energy-efficiency, improved gain and low level of noise contribution, when compared to the state-of-the-art in this field. In this paper, two fully-differential implementations are presented, a first one with a double CMOS branch biased by two pairs of voltage-combiners structures in both NMOS and PMOS configurations, and a second one with folded voltage-combiners specifically targeting low voltage applications, e.g., supplies below 1 V. The usage of voltage-combiners to bias the OTAs improves the gain and the gain-bandwidth product, therefore improving the energy-efficiency figure-of-merit. High values of figure-of-merit are achieved in both implementations, i.e., more than 1600 MHz × pF/mA and 2000 MHz × pF/mA, gain values above 53 dB and 50 dB under supply sources of 2 V and 0.7 V respectively. The folded voltage-combiners biased OTA is able to operate correctly under a voltage supply down to 0.7 V with proper DC biasing. The results are finally compared with state-of-the-art in this field and the potential of the circuits is fulfilled using a state-of-the-art layout-aware integrated-circuit optimization framework, AIDA, particularly relevant in order to overcome the device stacking problematic for lower voltages.