Distribution Line Carrier Sensitivity Analysis Using Bus Impedance Matrix

In a previous paper[1] we described the use of a bus impedance matrix approach for determining the signal strength of distribution line carrier signals. The technique used bus impedance matrices to calculate transimpedances which are the ratios of the voltage at any point on the line to the current injected at any point on the line. In the current paper we apply sensitivity analysis to this bus impedance approach and show how simply new transimpedances can be obtained from the original values when changes in the distribution line are made.     

小电流接地配电网馈线单相接地故障零序阻抗特性分析

文章以暂态零序特征为着眼点,从频域角度对小电流接地系统发生单相接地故障后的特性进行详细探讨。文章从线路入端零序阻抗这一随频率变化的特征量入手,深入挖掘了配电网系统中各馈线零序阻抗的阻抗特性,详细探讨了零序阻抗的幅值、相角随频率的变化规律,并针对不同的中性点接地方式以及线路是否健全加以分析,为更好得利用零序暂态信号,提高故障检测正确率夯实了基础。最后通过PSCAD搭建仿真模型验证了该特性。     

基于多点频谱法的电池一致性分类研究

为了有效地对电池一致性进行分析,借助了电化学阻抗谱手段,利用阻抗谱对电极系统综合分析的能力可以准确反映电池内部成分的变化。为了使其更接近于实际生产使用,针对用时长,分选难度大等缺点进行改进;研究中选取特定频谱测量电池阻抗,用测量结果来模拟阻抗谱曲线,以此对电池进行分选。从实际数据可知改进后该方法能够快速简洁地对电池进行分选并能够产生良好效果。     

提高并网逆变器在弱电网下稳定性的虚拟阻抗附加相角补偿控制

在LCL型并网逆变器中,为了减少传感器的使用,并网电流反馈的闭环控制得到了广泛的应用。然而一方面LCL型并网逆变器自身存在谐振现象,从而限制了电流控制器的设计;另一方面,由于弱电网中电网阻抗的存在,使该控制性能下降,对系统稳定产生不利影响。针对上述问题进行改进：一是采用特定的并网电流反馈有源阻尼控制器来虚拟电网侧的串联阻抗,即基于有源阻尼的虚拟阻抗法来抑制谐波尖峰;二是采用相位超前补偿的方法,增大逆变器输出阻抗的相角,极大地减少不稳定区域。保证了当电网阻抗变化时,该系统仍具有较强的稳定性。最后在MATLAB/Simulink上进行仿真,验证了所提方法的有效性和可行性。     

基于DBSCAN聚类和数据筛选的系统谐波阻抗估算

系统谐波阻抗是谐波发射水平估计和责任划分的关键参数,传统的估计方法通常适用于系统阻抗恒定和背景谐波电压波动较小的条件.然而运行方式改变、投切阻抗等因素会导致系统阻抗变化,谐振、谐波波动性等现象会导致背景谐波电压有较大范围波动.因此,提出一种基于DBSCAN聚类和数据筛选的系统谐波阻抗估算方法,当系统阻抗变化时,DBSC...     

Neck electrical impedance for measurement of swallowing

Recently, videofluorography has been used for evaluation of swallowing function in the rehabilitation field. But it is not easy to evaluate swallowing disorders simply. In addition, there are problems of exposure for daily use. We have proposed a measurement method of swallowing using bioelectrical impedance (impedance pharyngography, IPG) which has advantages of easy handling and noninvasive measurement. Appropriate electrode position have been determined. The waveforms of IPG can be obtained with some extent reproducibility. The change of neck electrical impedance in the pharyngeal phase is mainly caused by the changes of equivalent cross sectional area near the epiglottis. The possibilities of applications for clinical diagnosis have been shown. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 35–44, 2000     

Decoupled control of grid connected inverter with dynamic online grid impedance measurements for micro grid applications

This paper presents a decoupled control of grid connected inverter using dynamic online grid impedance measurements for a micro grid application. The proposed controller is implemented in synchronous reference frame (SRF) and controlled using linear PI controllers. The mutual coupling introduced between the d and q control loops due to the transformation into SRF is accurately decoupled using the dynamically measured grid impedance using a feed-forward control. The decoupling allows independent control of active and reactive powers against step changes in the active/reactive power references. The online measurement of the actual impedance and its use further for decoupling is proposed in this paper for making the decoupling accurate inspite of the network configuration being altered like in micro grids. Here the grid resistance and inductance are measured during the operation using a non-characteristic frequency current continuously injected into the grid, and subsequently calculating the impedance using discrete Fourier transforms. The continuous injection of non-characteristic current at 75 Hz avoids the injection of sub-harmonics into the grid during measurements. The control loop is updated periodically with the estimated grid impedance, thus enabling the independent control of active and reactive powers delivered by the inverter. The proposed decoupled controller with grid impedance measurement is tested through simulation studies and hardware experiments. The experiments are conducted with the proposed controller on a scaled down laboratory model of micro-grid with a 1 kVA solar inverter, and the performances are presented for step changes in the power references and the results are presented.     

含SVG的双馈风场风速变化条件下高频谐振问题分析

大规模风电并网导致宽频谐振问题日渐凸显,业内多认为电缆电容效应、控制器参数变化等是导致谐振的主要因素,而关于静止无功发生器(static var generator, SVG)、风功率变化与高频谐振内在因果关系研究尚未展开。针对低风速风场系统高频谐振问题,首先基于谐波线性化理论,考虑功率外环作用,建立SVG和双馈风机(doubly-fed induction generator, DFIG)的序阻抗模型。其次将风速变化纳入风机变流器建模,并建立空载电缆投入时风速变化与SVG阻抗的联系。然后利用阻抗交互揭示风机变流器阻抗变化对SVG阻抗特性的影响机理,指出区域内空载电缆投入后,低风速不仅降低系统在高频的鲁棒性,而且扩大了SVG高频负阻尼范围,导致系统高频谐振风险增加。最后,基于STARSIM-HIL搭建含SVG的双馈风场电磁仿真模型,并进行软硬件在环实验。实验结果证明了理论分析的正确性。     

关于工频变化量阻抗继电器的校验方法探讨

目前工频变化量阻抗继电器广泛应用于中、高压线路保护,工频变化量阻抗保护在许多厂家的保护装置都有使用,但在实际校验工作中,其阻抗动作特性和整定值动作边界校验离散性很大;通过分析工频变化量阻抗继电器的动作方程推导出工频变化量阻抗继电器的校验公式,通过多年来实际现场校验的经验和方法,对目前文献介绍的两种工频变化量阻抗继电器的现场校验方法进行了对比分析,提出了现场建议使用的校验方法。     

基于虚拟阻抗参数优化的并联逆变器控制研究

无互联线的并联逆变器以其冗余度高、灵活性好等优点备受关注。但是由于无信息的交流,逆变器本身参数、线路阻抗、参考电压等因素的差异可能引起逆变器间的环流流动。基于虚拟阻抗的并联逆变器控制方式可降低系统对上述差异的敏感度,减小逆变器间的环流。但是传统虚拟阻抗的参数通过经验和逆变器等效阻抗的波特图选取,参数往往非最优化,均流效果的动态性能也不理想。通过分析逆变器等效阻抗的零极点位置变化对系统稳态及暂态性能的影响,提出了一种优化虚拟阻抗系数的方法,有效地改善了逆变器的动态及稳态性能,提高了多逆变器并联运行的稳定性。建立两个逆变器并联的拓扑结构,通过仿真结果的分析验证了所提方法的可行性和正确性。     

Effectiveness of non-penetrating electroporation applicators to function as impedance spectroscopy electrodes

Electroporation is commonly performed to deliver drugs and genes to cells comprising tissues. A possible way to control and confirm delivery is through the use of impedance spectroscopy. Ideally, this tool should not interfere with delivery and should incorporate the use of electrodes, applicators, used for delivery. This work examines impedance spectra obtained with non-penetrating surface applicators commonly used for skin electroporation. After collecting and processing over 9,000 spectra from three animal models it was determined that the electrode systems tested would have no significant effect on the obtained spectra. Therefore, electroporation applicators currently in use could be used concurrently for the collection of impedance spectra.     

屏蔽对称数字通信电缆转移阻抗的测试研究

本文讨论了基于"三同轴法"屏蔽对称数字通信电缆转移阻抗的测试原理,并介绍了使用矢量网络分析仪作为信号源及接收器实现转移阻抗的测试;着重讨论了影响屏蔽数字电缆转移阻抗测试结果的因素。     

A generalized computer technique for the development of the three-phase impedance matrix for unbalanced power systems

This paper presents the development of the three-phase bus impedance and bus admittance matrices for unbalanced power systems. The imbalance conditioned by large single-phase loads, untransposed feeders, bundled conductors, etc., is reflected in the polyphase impedance or admittance matrix. The method utilizes the phase frame representation of network elements. Consequently, line removals or additions, impedance changes, conductor and phase openings can be simulated easily by modifying the bus impedance matrix. Thus, the proposed method makes it possible to analyze any type of single- or three-phase loads and unequal mutual coupling between the phases for large-scale power systems.     

纯电动汽车充电机输出阻抗特性

纯电动汽车充电机与汽车动力电池构成级联式供电系统.充电机的输出阻抗是随频率变化的函数,动力电池也在不同频率下表现出不同的阻抗特性.为了在充电过程中充电机与动力电池组成的系统能够稳定工作,必须保证充电机输出阻抗与电池输入阻抗的比值满足奈奎斯特稳定性判据.以纯电动汽车充电机的输出阻抗为研究对象,建立充电机动态线性小信号模型,通过仿真分析输出阻抗特性随直流工作点,输出滤波器等效串联电阻,控制环路特性的变化规律,并用实验证明了理论分析的正确性,为充电机输出输出阻抗的设计提供了依据.     

基于探针阵列的RF天线阻抗测量方法的研究

为研究等离子体放电期间大功率RF天线阻抗变化和满足阻抗匹配器的动态调节的需要,提出了基于探针阵列的RF天线阻抗的测量方法,利用传输线理论,分析了采用探针阵列对大功率RF天线的阻抗进行实时测量的原理,建立了数学模型,构建了天线阻抗的测量系统.该系统集数据采样、数据处理、参数计算等功能于一体,实现了大功率RF天线阻抗的自动测量,给出了系统的实时测量结果.实验结果表明该方法结构简单、可靠、测量精度高、速度快,具有良好的实用价值.     

基于PSO的低压电力线载波通信阻抗自适应匹配

低压电力线载波通信的阻抗匹配电路通常为一个固定的无源电路。设计了基于粒子群算法（particle swarm optimization,PSO）的自适应阻抗匹配系统,并建立了目标函数,通过调节π型无源网络中的电容值来匹配负载阻抗的变化。对负载阻抗为容性、阻性和感性时的电力线载波通信网络仿真,选择载波频率点为150 kHz、260 kHz和480 kHz。结果表明,目标函数均在迭代20次后逐渐取得最优值,证明基于π型无源网络的粒子群算法能够较好的自适应匹配负载阻抗的变化。     

含光伏电站的电网自适应接地距离保护研究

光伏电站并网使110 kV系统拓扑结构发生变化,同时光伏电站等效阻抗随运行方式的不同而改变,线路原有的距离保护受到影响。根据光伏电站的运行特性,推导了距离保护测量阻抗与光伏电站等效阻抗的关系,并对保护测量阻抗受到影响的机理进行了分析。根据不同运行方式下计算得到的光伏电站等效阻抗,提出了基于修正测量阻抗的自适应接地距离保护方案,使保护能够适应光伏电站运行方式的多样性,并且无需改变保护的整定值。在PSCAD/EMTDC中搭建了某地区光伏电站接入110 kV电网的实际拓扑结构并进行仿真分析,分析结果验证了所提方法的有效性和优越性。     

应用在高压直流输电系统中的混合型有源滤波器稳定性分析及控制方法

分析了混合型有源滤波器HAPF(hybrid active power filter)在高压直流系统应用时的稳定性问题,其中HAPF采用H桥级联变换器与LC滤波器组合的方案,对高压直流系统的特征谐波电流进行滤波。为了分析在电网阻抗变化时HAPF出现的谐波谐振现象,对HAPF进行了阻抗建模,基于阻抗模型的分析结果,采用了具有延时补偿功能的谐振调节器对阻抗特性进行修正,并从提高稳定性角度提出了相应的控制参数设计方法。阻抗模型分析结果表明,控制系统延时产生的负阻尼是引发稳定性问题的主要原因,采用改进后的控制方法可以将延时产生的负阻尼修正为正阻尼,能够有效避免谐波谐振。在PSCAD中进行仿真建模,并通过阻抗扫描验证了有源滤波器的阻抗特性。仿真案例证实了控制方法的有效性。     

变压器阻抗兼作滤波装置电抗

自耦调压变压器的补偿绕组是一个大阻抗,在补偿绕组安装滤波装置必须考虑补偿绕组阻抗的影响,并以有效利用来提高滤波效果和降低造价。     

继电保护整定计算中故障计算模型的选择与比较分析

计及运行方式变化的故障计算的快速实现是提高继电保护整定计算工作效率的关键。根据整定计算中故障计算的特点,基于节点阻抗矩阵,提出了计及运行方式变化的大批量故障快速计算的实现方法,通过涉及节点集的合理选取和阻抗矩阵的分级存贮,实现阻抗矩阵的最小修改,从而达到故障计算的快速及实用性要求。并从时间复杂度的角度分析和比较了基于节点导纳矩阵和节点阻抗矩阵的故障计算在整定计算中应用的差异。