High Impedance Fault Detection of Distribution Network by Phasor Measurement Units

This paper proposes a new algorithm for High Impedance Fault (HIF) detection using Phasor Measurement Unit (PMU). This type of faults is difficult to detect by over current protection relays because of low fault current. In this paper, an index based on phasors change is proposed for HIF detection. The phasors are measured by PMU to obtain the square summation of errors. Two types of data are used for error calculation. The first one is sampled data and the second one is estimated data. But this index is not enough to declare presence of a HIF. Therefore another index introduces in order to distinguish the load switching from HIF. Second index utilizes 3rd harmonic current angle because this number of harmonic has a special behaviour during HIF. The verification of the proposed method is done by different simulation cases in EMTP/MATLAB.

Improvement Design of Biochip Towards High Stable Bioparticle Detection Utilizing Dielectrophoresis Impedance Measurement

Dielectrophoresis impedance measurement(DEPIM)is a powerful tool for bioparticle detection due to its advantages of high efficiency,label-free and low costs.However,the strong electric field may decrease the viability of the bioparticle,thus leading to instability of impedance measurement.A new design of biochip is presented with high stable bioparticle detection capabilities by using both negative dielectrophoresis(nDEP)and traveling wave dielectrophoresis(twDEP).In the biochip,a spiral electrode is arranged on the top of channel,while a detector is arranged on the bottom of the channel.The influence factors on the DEP force and twDEP force are investigated by using the basic principle of DEP,based on which,the relationship between Clausius-Mossotti(CM)factor and the frequency of electric field is obtained.The two-dimensional model of the biochip is built by using Comsol Multiphysics.Electric potential distribution,force distribution and particle trajectory in the channel are then obtained by using the simulation model.Finally,both the simulations and experiments are performed to demonstrate that the new biochip can enhance the detection efficiency and reduce the negative effects of electric field on the bioparticles.

Longitudinal impedance measurements and simulations of a three-metal-strip kicker

A kicker is a critical component for beam injection and accumulation in circular particle accelerators. A ceramic slat kicker plated with a TiN conductive coating was applied in the Beijing Electron Positron Collider (BEPCII). However, the ceramic slat kicker has experienced several sudden malfunctions during the operation of the BEPCII in the past. With a reliable kicker structure, a three-metal-strip kicker can substitute the original ceramic slat kicker to maintain the operational stability of the BEPCII. A comparison of the numerical simulation was conducted for three kicker models, demonstrating the comprehensive advantage of the three-metal-strip kicker. Furthermore, impedance bench measurements were conducted on a prototype of a three-metal-strip kicker. The longitudinal beam-coupling impedance was measured using a vector network analyzer via the coaxial wire method. A satisfactory agreement was obtained between the numerical simulations and measurements. Based on the numerical simulation data, the loss factor was 0.01721 V/pC, and the effective impedance was 3.59 mΩ(σ=10 mm).The simulation of the heat deposition on each part of the kicker demonstrated that 84.4%of the parasitic loss of the beam was deposited on the metal strips, and the total heat deposition power on the kicker was between 113.3 and 131.5 W. The obtained heat deposition powers can be considered as a reference for establishing the cooling system.

In Situ Acquisition of Equivalent Circuit Parameters of Crystal Resonance during Copper Deposition and Dissolution in Acidic Solution by Electrochemical Quartz Crystal Impedance System

Electrochemical quartz crystal impedance system (EQCIS) which allows in situ dynamic quartz crystal impedance measurement in an electrochemical experiment was developed by combining an HP 4395A Network/Spectrum/Impedance analyzer with an EG&G M283 potentiostat. Equivalent circuit parameters of crystal resonance change significantly during electrodeposition and dissolution of copper in 0.1 mol/L H2SO4 aqueous solution in a cyclic potential sweep experiment, which is explained with an overall picture of mass loading, solution density and viscosity, etc..

Development of Instrumentation for the Measurement of the Performance of Acoustic Absorbers

In both fixed and rotary wing aircraft, the move toward lighter structures has resulted in an increase in structural vibration and interior noise. Porous materials have been proposed as acoustic absorbers to reduce this noise. This paper discusses the development of equipment at the NASA Glenn Research Center for characterizing the acoustic performance of porous materials: a flow resistance apparatus to measure the pressure drop across a specimen of porous material, and a standing wave tube that uses a pair of stationary microphones to measure the normal incidence acoustic impedance of a porous material specimen. Specific attention is paid to making this equipment as flexible as possible in terms of specimen sizes need for testing to accommodate the small or irregular sizes often produced during the development phase of a new material. In addition, due to the unknown performance of newly developed material, safety features are included on the flow resistance apparatus to contain test specimens that shed particles or catastrophically fail during testing. Results of measurements on aircraft fiberglass are presented to verify the correct performance of the equipment.

RESEARCH ON INPUT IMPEDANCE OF DIPOLE ANTENNA IN GTEM CELL

The formula of input impedance of dipole antenna in Gigahertz Transverse ElectroM agnetic(GTEM) cell based on the dyadic Green's function is first obtained in this paper. The validation of the formula is verified by the results of theoretical derivation and simulation with well agreements. In comparison with the formula of input impedance in free space, the relationship between the change of input impedance with the length of antenna and the position of antenna in GTEM cell is obtained. In addition, some meaningful conclusions are presented, which not only can be referred by the further research of ElectroM agnetic Interference(EMI) measurements in GTEM cell, but also provide the theoretical basis for testing compensation and error analysis.

Nucleation and Growth of Thallium on Thin Film Mercury Electrode: Voltammetric, Scanning Electron Microscopy, Chronoamperometric and Electrochemical Impedance Studies

Thallium is a heavy metal highly toxic to the biosphere. It can be determined by anodic stripping voltammetry after deposition on mercury film. The aim of this work is to study the conditions and mechanisms of deposition of Hg on glassy carbon electrode and Tl on Hg film by cyclic voltammetry, scanning electron microscopy, chronoamperometry and impedance techniques. The results showed a germination and growth of a 3D Hg phase on glassy carbon electrode. Similarly, the electrodeposition of Tl on Hg follows a 3D three-dimensional nucleation with diffusion controlled growth. The impedance measurements reveal an easier charge transfer on the Tl film.

Online Measurements of High-band Grid Impedance Using Variable Frequency Carrier Based PWM Schemes

Grid-connected power electronic devices, such asvoltage-source inverters (VSIs), are increasingly installed in thegrid for the utilization of renewable energy sources. Under highpenetration, the weak grid contains plentiful harmonics and complexgrid impedance values, which have deep impacts on systemstability as well as its control performance. Online impedancemeasurement is needed for impedance based adaptive controland analysis. This paper proposes a variable carrier frequencyPWM (VCFPWM) based online grid impedance measurementtechnology. This method broadens the available working rangein the high frequency band without increasing the low bandperturbations. Through good analysis and design of the carrierfrequency, the VCFPWM method injects sufficient harmonicenergy at specified high frequency points and guarantees lowTHDs at the same time. The detailed design considerations ofthe carrier frequency are clarified and the characteristics of theVCFPWM based excitations are analyzed in this paper. Finally,the simulation and experimental results based on a three-phasegrid-connected VSI are presented to verify the effectiveness ofthe proposed method.

Research on Time-Domain Transfer Impedance Measurement Technology for High Frequency Current Transformers in Partial Discharge Det ection of Cables

We focus on the high frequency current method which is widely applied in the partial discharge(PD)detection of cables.Aiming at guaranteeing the accuracy of this method,we study an innovative time-domain technology for effectively measuring the transfer impedance of the high frequency current transformers(HFCTs).The proposed technology called pulse injection method obtains the system response under the excitation of the wide-band instantaneous pulse signal.Firstly,by studying the working principle of HFCTs,we summarize that the bandwidth of the selected signal acquisition device should be at least 100 MHz to ensure measurement accuracy.Secondly,Gauss pulse and square wave pulse are generated to determine the effects of different sources.The measurement results indicate that Gauss pulse is more suitable for pulse injection method,and the rise time should be under 10 ns to improve the starting frequency of oscillation distortion.Finally,the transfer impedance curves of five types of HFCTs are acquired by both pulse injection and traditional point-frequency methods.The measurement results show a remarkable consistency between two methods.However,pulse injection method requires the simpler operation and lias a higher resolution,obviously improving the measurement efficiency and bet ter displaying the details of the transfer impedance curves.

基于阻抗在线测量的锂离子电池过放电诱发内短路识别研究

锂离子电池的过放电行为可诱发内短路进而可能导致热失控。由于单体电池一致性差异和过放电导致的内短路初期电、热特征不明显,使得电压和温度等常规物理参数难以可靠实现故障预警,而阻抗可以反映电池内部信息,对故障状态具有较好的指示能力。该文通过分析锂离子电池过放电诱发内短路引起阻抗变化的机理,基于设计的阻抗在线测量装置,确定用于监测电池内短路故障的特征阻抗频率为70 Hz,获取过放电诱发内短路过程中特征频率下动态阻抗及阻抗变化率,提出一种基于动态阻抗特征的内短路在线识别方法并验证了方法的可靠性。实验结果表明,锂离子电池放电过程中动态阻抗半正弦变化特征可提前约144 s实现过放电预警,动态阻抗针状变化特征可提前约152 s实现内短路故障预警,动态阻抗明显回升特征可作为内短路发生的标志。此外,阻抗变化率特征有助于实现锂离子电池故障识别及预警,该方法在锂离子电池故障在线快速诊断中具有重要的应用潜力。

Using the system function to analyze the performance of transducer's impedance measurement method

Prom investigation of the advantages and disadvantages of conventional tri-voltage method,a method for the measurement of the transmitting transducer＇s impedance was presented to solve the difficult problem of examining the consistency of the transmitting phased array on the single-mode excitation sea spot.In the method based on the system function, the circuit structure of tri-voltage method was used but new parameters were measured.The principle of the method was given first.Then when resistors with different nominal values were used in the circuit,the measured results for the impedance of transducers were reported.The results were compared with the higher precision impedance analyzer.Finally,the error analysis was performed according to the impedance formula and the equivalent circuit parameters were fitted.Under the condition of guaranteeing the sampling precision,by performance analyzing, the resistor value in series was chosen relatively smaller than the impedance of transducer,the measurement of impedance could achieve the same precision as the higher precision impedance analyzer.Finally,the least squares curve-fitting of measured curves indicated that the transducer equivalent electrical parameters could be extracted accurately and used to design the matching network.

多尺度注意力融合与视觉Transformer方法优化的电阻抗层析成像深度学习方法

电阻抗层析成像(EIT)具有显著的可视化和非侵入性等特点,在工业和生物医学工程领域展现了其广阔的应用潜力。由于其逆问题存在高度非线性和病态性特点,导致了数值成像方法在空间分辨率上的局限性,尤其是在多相介质分布情况下,现有EIT技术在成像过程中出现边界失真和电导率误差,从而影响最终的成像精度。本文提出了一种基于卷积注意力机制的U型深度成像方法——MAT-UNet,将卷积块注意力模块(CBAM)与U-Net结构相结合,在特征提取与融合过程中嵌入卷积块注意力模块,以增强模型的注意力定向和特征表征能力,同时跳跃连接引入了压缩-激励(SE)注意力机制与视觉Transformer(ViT)来优化全局特征的学习,使用多头交叉注意力模块(MHCA)实现编码器与解码器的多尺度信息融合。MAT-UNet通过大量的仿真数据训练获得最优模型参数,并在多样化复杂形状和肺部仿真模型进行了实验验证。定量评估指标表明,该方法在重建图像中的均方根误差(RMSE)结果为2.3156,结构相似性指数(SSIM)结果为0.9437,可视化结果与真实分布和边界具有很好的一致性。实验结果表明,本文提出的MAT-UNet模型展现出良好的鲁棒性和泛化能力,相较于传统的单一卷积结构,集成Transformer结构提供了更精准的EIT图像重建效果,在无损测量与检测应用中存在很大的潜力和价值。

基于多正弦信号注入的大功率并网逆变器电网阻抗在线测量技术研究

文中研究基于多正弦扰动信号注入的大功率并网逆变器电网阻抗测量技术。选取多正弦信号作为电压扰动,参考空间光场理论中的Gerchberg-Saxton相位恢复算法对扰动信号进行优化设计;剪辑函数作为其中的关键要素,能够决定扰动信号时域波峰的剪辑速度和剪辑能力;为提升上述性能,提出采用反正切函数代替传统算法中的对数剪辑函数,仿真结果表明,相位恢复算法的剪辑性能得到大幅提升;随后,通过逆变器将扰动信号注入电网,采用Gauss-Newton非线性最小二乘法对采集到的扰动信号特征谐波频率点的信息进行曲线拟合,获取当前电网阻抗信息;最后,于搭建的1.5 MW并网逆变器RT-Lab平台进行多弱电网场景下的阻抗测量实验,实验结果验证了此方案的有效性和准确性。

基于阻抗测量信息的电气化铁路“多车共网”系统稳定性分析

阻抗测量技术能够准确地获取“牵引供电网-列车”(简称“车-网”)系统的宽频阻抗特性,但在阻抗测量信息的利用方面目前多是针对单车系统的稳定性分析,缺少对“多车共网”系统宽频稳定性问题的分析。因此,该文提出一种基于牵引供电网与列车阻抗测量信息的“多车共网”系统稳定性分析方法。首先,利用阻抗测量的方式获取牵引供电网节点阻抗矩阵与列车阻抗信息;然后,建立“多车共网”系统模型,采用基于阻抗回差矩阵行列式的稳定性分析方法,分别从低频到高频分析了电气化铁路中低频振荡、谐波谐振和谐波不稳定三类典型振荡问题,并给出相关的振荡信息,实现多类稳定性问题的统一分析;最后,利用Matlab/Simulink仿真验证了所提稳定性分析方法的有效性。

基于多电平滞环电流控制的牵引供电系统可控宽频带阻抗测量技术

精确获取牵引供电系统的宽频带阻抗特性,是分析车-网耦合系统的宽频带振荡问题的关键途径,对保障电气化铁路的安全稳定运行具有重要意义。目前的阻抗测量技术大多难以兼顾大功率与频带可控的测量要求,因此,该文提出一种基于多电平滞环电流控制的牵引供电系统可控宽频带阻抗测量技术,测量频带为10 Hz~5 kHz,可通过一次谐波扰动注入快速获取目标频带的系统阻抗,相比于传统的滞环电流控制方法,具有更低的开关频率,并且能有效避免死区效应,改善输出电流的波形,更适用于宽频信号的跟踪控制。最后,通过仿真和硬件在环实验验证了该测量技术的有效性。

面向新鲜乳品质量检测的RFID传感器设计

针对新鲜乳品质量便捷测量的需求,提出一种基于电容传感器阻抗分析以及射频识别能量与数据传输的柔性射频识别传感器标签。设计并优化了叉指电容传感器前端,通过阻抗分析感知乳品质量变化。通过天线仿真优化提高无线供电效率,利用近场通信数据交换格式归一化数据实现无线传输与显示。通过研究传感器前端和高频天线线圈屏蔽作用并对其优化改进,提升了传感器的抗干扰能力。利用pH值作为参考值确定乳品变质时间节点,并对所提出方法进行了实验验证,结果显示传感器标签在1.5cm内能够稳定工作,测量最大相对误差为3.28%,新鲜度判断结果能够有效反应乳品实际变质情况。

浮选槽液位高度和泡沫层厚度测量系统设计

在金矿浮选过程中,矿浆液位高度和泡沫层厚度是一个关键的技术参数,对金矿的出金率有很大影响。针对浮选槽中泡沫层厚度难以测量的问题,设计了一种基于阻抗测量的金矿浮选槽液位高度及泡沫层厚度测量系统。该系统使用32个电极测量31组阻抗数据,根据浮选槽矿浆与泡沫导电性能不同的特点,通过阻抗分析仪判断各电极所处位置并计算得出液位高度和泡沫层厚度。经实验验证,该系统可直接测量出液位高度和泡沫层厚度且效果理想,为金矿浮选中液位的实时控制提供了基础。

锂离子电池阻抗在线测量装置设计

锂离子电池的交流阻抗能够反映电池内部信息,是电池状态在线监测的有力工具。阻抗在线测量装置的设计是实现基于阻抗的电池状态在线估计及故障预警技术的关键。本文基于嵌入式微控制器设计了锂离子电池交流阻抗在线测量装置,采用全相位快速傅里叶变换算法将时域数据转换到频域,并对转换结果进行插值运算,实现了0.01 Hz~10 kHz频率范围内交流阻抗的在线测量,有效解决了当前阻抗在线测量装置基于传统快速傅里叶变换算法所产生的频谱泄露、栅栏效应以及相位计算不准确的问题。通过对不同容量、不同正极材料的电池进行静态和动态阻抗测量,验证了装置的可靠性与快速性,并且放电末期动态阻抗急剧变化特征对电池的状态具有一定的指示能力。本文设计可方便集成于电池管理系统中,在锂离子电池状态在线估计及故障预警等方面具有一定的应用价值。

频率波动下基于并网逆变器的电网阻抗在线测量方法

电网频率波动和测量频率对电网工频阻抗的准确测量有着较大的影响。为此,对影响电网阻抗测量准确度的主要原因进行了理论分析,提出了一种基于互补电流信号注入的在线阻抗测量方法。该方法通过在基波电流相位相同处注入相邻的两段互补扰动电流,运用基波消去的方法降低了基波泄漏影响,相对地提高了测量信噪比;在减小电网频率波动对测量影响的同时,使测量频率可以更加接近工频。通过对比仿真和实验,证明该方法在实际电网工频阻抗测量中具有更高的准确度。

基于复频率信号注入的直流接地极线路故障测距方法

在直流输电系统接地极线路配备阻抗监视系统的背景下,可利用高频测量阻抗特性实现故障距离的精确计算。然而,分析发现直流系统接地极线路在不同故障条件下可能产生相同的高频测量阻抗,这意味着测量阻抗与故障距离间不是一一映射关系,由单一测量阻抗难以得到准确的故障距离。文中分析了高频测量阻抗的重合特性随注入信号变化的特征,提出了基于复频率信号注入的故障测距方法,并给出了复频率的选定策略。该方法改进了基于高频测量阻抗幅相特性的接地极线路故障测距方法,实现了故障位置的准确计算。最后,通过仿真算例充分验证了所提测距方法的可行性和精确性。