Calculation method for estimating thermal impedance for pulse current of power semiconductor devices

Contents The described method is valid for arbitrary wave forms of the constant pulse current and for all diode, transistor and thyristor family devices whose thermal circuit can be modelled electrically by the serial connection of resistor-capacitor RC-pairs and whose forward characteristic can be approximated by slope resistance and threshold voltage. Temperature dependence of the device's thermal circuit parameters and temperature dependence of the forward characteristic parameters were not taken into consideration. The method enables an estimate to be made of the influence of current amplitude on the value of thermal impedance for pulse current.

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Eine Rechnungsmethode zur Bewertung der thermischen Impedanz für Impulsstrom von Leistungshalbleiterkomponenten

Übersicht Die vorgestellte Methode ist für beliebige Impulsstromform und zwar für alle Komponenten aus den Dioden-, Transistoren- und Thyristoren-Familien geeignet, deren thermischen Kreis man durch Serienschaltung von RC-Gliedern elektrisch modellieren und die Durchlaßkennlinie durch Ersatzwiderstand und Schleusenspannung approximieren kann. Die Temperaturabhängigkeit der Parameter der Durchlaßkennlinie der Komponente wird nicht berücksichtigt. Die Methode erlaubt eine Abschätzung des Einflusses der Stromamplitude auf die thermische Impedanz für Impulsstrom.

     

基于纵联阻抗幅值的输电线路纵联保护

提出了一种基于纵联阻抗幅值的输电线路纵联保护,该纵联阻抗是由线路两端各相电压故降分量差与电流故障分量和的比值计算而来的,利用这个阻抗的幅值判断故障是否发生在区内.区外故障时,上述阻抗的幅值明显大于全线串联正序阻抗的幅值;区内故障时,该阻抗的幅值明显小于上述定值,该保护不仅易整定、具有自选相功能,性能稳定,动作灵敏、适应性强,而且能有效抵御由线路电容电流和CT饱和所带来的影响.在EMTP数字仿真和动模试验中,建立一条1000 kV、500 km和一条500 kV 50 km输电线路的模型,后者还考虑了CT饱和,使用兰州东至咸阳750 kV的动模数据,进行了各种故障下仿真,结果表明所述纵联保护都能正确标示各种故障状态.     

Investigation of transient responses of nanoscale transistors by deterministic solution of the time-dependent BTE

In this work, the transient characteristics of nanoscale field-effect transistors (FETs) have been investigated using a deterministic solver based on the time-dependent multi-subband Boltzmann transport equation (BTE). The response to a step signal superimposed on the gate or drain electrode is simulated. The transient process can be understood as a combination of electrostatic and transport relaxation. The extracted transient relaxation time for the drain current, which is unrelated to the direct-current (DC) shift, is important for transient device modeling.     

Surge impedance of independent transmission towers characterized by the direct method

Measurement of the surge impedance of a transmission tower by the direct method is studied with the help of NBC-2. The arrangement of the measuring wires in the experiment influences the result, and it is possible to correct the measured tower surge impedance to that for a standard arrangement with a vertical current injection wire and a horizontal voltage measuring wire. By reviewing various experimental results in this way, it is concluded that an independent double-circuit transmission tower has an impedance of about 150 Ω with the traveling wave speed in the tower being equal to that of light. This value can be applied to the case of a direct lightning hit on the tower top, regardless of the type of lightning, upward or downward. © 1998 Scripta Technica. Electr Eng Jpn, 122(4): 17–24, 1998     

交流阻抗谱法研究燃料电池的极化阻力

电化学阻抗谱(Electrochemical Impedance Spectroscopy,EIS)是用于研究燃料电池电性能的一种重要手段,因其包含了大量的电池极化阻力等方面的信息。通过对电化学阻抗谱的分析可以得到电池的欧姆极化电阻、电化学极化电阻和浓差极化电阻等数据。分析了固体氧化物燃料电池常见的各种形状的交流阻抗谱,给出了各自的等效电路,并通过对等效电路的拟合求得了电池的极化电阻。与文献中普遍采用的直接读图法相比,拟合法得到的电池极化电阻数据更准确、更合理。     

Investigation of phase distribution in nanoscale BaTiO3 powders prepared by hydro-thermal synthesis

Nanoscale BaTiO₃ powders were prepared by hydro-thermal synthesis; a mixture of H₂O and EtOH was used as solvent and the phase distribution of the powders was investigated in terms of the ratio (R) of DI water, H₂O/(H₂O+EtOH). The size of the powders was varied in the range of 20～100 nm depending on the solvent condition. X-ray diffraction and Raman spectroscopy were applied to investigate the variation in the relative volume fraction of the tetragonal phase; most of the powders contain both tetragonal and cubic phases. The results obtained by the two different analysis methods appear to be very close to each other, and it was found that the maximum volume fraction of the tetragonal phase was 23～26% when the synthesis was performed at R?=?0.25～0.5.     

利用合成宽带信号获取PEMFC阻抗谱方法

燃料电池的"健康状况"可以通过研究其阻抗来确定,通常使用的是阻抗谱(IS)法,它使用的是正弦信号扫描方式。阻抗谱是依据电池的电化学状态,基于频域内测量电池的复阻抗。阻抗谱法的主要优势是其结果与理论值的准确性。提出了一个创新的方法去测量阻抗谱。介绍了使用一种交替的正弦信号(频域合成宽带信号)可大幅减少测量时间的方法。在测试过程中,在频域建立了一种理论上的合成宽带信号,信号被转换成时域信号,将被用作对燃料电池的激励,捕获电池输出电压响应,这个响应的频率与激励信号的范围是一样的,从而实现阻抗的测量。该系统已建立并且对质子交换膜燃料电池阻抗测试达到了很好的效果。     

Modelling of photonic bandgap devices by the leaky mode propagation method

Main modelling approaches used for investigating the Photonic bandgap (PBG) devices are reviewed. In particular, the model based on Leaky Mode Propagation (LMP) method is described. A complete analysis of the propagation characteristics, including the determination of modal propagation constants, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, total forward and backward power flow in the structure, guided and radiated power, and total losses, can be carried out by a computer program based on the LMP approach. The numerical results have been validated by comparisons with those obtained by using other more complex and expensive models. The new model shows some significant advantages in terms of very low computational time, absence of any a priori theoretical assumptions and approximations, capability of simulating the actual physical behaviour of the device and fast determination of the bandgap position.Copyright © 2003 John Wiley & Sons, Ltd.     

基于正序阻抗幅值比的风电场送出线路纵联保护

针对风电场送出线路纵联保护在数据延时传输及异常采样数据下保护性能不佳的问题,提出了基于正序阻抗幅值比的纵联保护。通过分析风电系统送出线路发生区内外故障时正序阻抗幅值特征,得出区内外故障下双端正序阻抗幅值差异比特征不同。引入综合层次聚类(balanced iterative reducing and clustering using hierarchies, BIRCH)方法剔除正序阻抗幅值序列中异常采样数据,形成不含异常采样数据的故障时间序列聚类特征,并结合双端正序阻抗幅值差异比特征,构造不受数据延时传输影响的纵联保护判据。仿真结果表明,所提出的纵联保护不受系统运行工况、故障类型、数据延时传输及异常采样数据的影响。在过渡电阻达到150  时,所提出的纵联保护仍能正确判别故障方向,具有较强的抗噪性能,适用于含风电接入的弱馈型电力系统。     

甲醛在Au/Ti电极上电氧化的交法流阻抗研究

采用电化学阻抗谱(EIS)研究了甲醛在Au/Ti电极上的电氧化过程,通过对Nyquist图的理论分析,求得一系列甲醛电氧化的动力学参数.运用R1[C1(R2W1)]形式的等效电路对甲醛电氧化的阻抗图谱进行了模拟,较好地解释了甲醛电氧化实验中的动力规律.同时考察了极化电位和甲醛浓度对电化学交流阻抗谱的影响,发现在极化电位-0.5 V时甲醛氧化最易进行,随着甲醛浓度的增加电荷转移电阻Rα不断减小.     

Investigation of shielding method of ELF magnetic field generated from conductors

We have studied experimentally the shielding method of ELF magnetic field applied to the source of line conductors. For the single‐phase line current, it appears to be difficult to achieve effective shielding. On the other hand, for the balanced three‐phase conductors, including triangle and twisted configuration, a certain reduction of generated magnetic field was achieved by adjusting the configuration of conductors or by surrounding the conductors with cylindrical shielding materials made of ferromagnetic materials or nonferromagnetic metals. Normalized characteristics between phase current, distance between source current and observation point, distance between phase conductors, and the pitch of twisted cable were derived. In addition, the effect of unbalanced current was also investigated. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 12–19, 2000     

Simplified impedance broadband matching by the image parameter method: The RC case

The image parameter theory is now considered as outdated for filter design owing to the existence of very efficient optimization procedures for the effective behaviour of filters. Nevertheless, it allows one to exhibit very simple relations between the bandwidth and the values of the components. Hence it is ideally suited for the problem of impedance broiband matching where the bandwidth and some components are specified data. It is shown that it allows to make a straightforward distinction between well- and ill-conditioned problems. In the first case the problem is reduced to a one-dimensional optimization and an image parameter design provides very easily an equalizer optimal for all practical purposes. In the second case the values of the image parameter design provides excellent initial values for an optimization process. The method is applied here to the simplest problem, the RC load. In a separate paper it will be shown that it is easily extended to more complicated loads and the double-matching problem.     

A delta‐method technique in the wavelet domain to determine statistical quantities of the response of electromagnetic devices with uncertain parameters

In this paper a method to determine the mean value and the variance of the response of a system with uncertain parameters is proposed. With the term ‘response of a system’ we indicate either the value of a single parameter that represents a figure of merit of a device (e.g. the efficiency of a transmission system or the band width of a communication channel) or a characteristic function of the system (e.g. the impulse or the frequency response). In the latter case we estimate the mean value and the variance at every sample of the response. The estimate is performed by using the delta method, a technique for approximating expected values of functions of random variables when the direct evaluation is not feasible. Two examples of the application of the proposed procedure are reported and the results are compared with simulations performed by a Monte Carlo analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

基于测试信号法的HVDC谐波阻抗扫描方法研究

谐波阻抗扫描是高压直流输电(HVDC)中谐波谐振分析、交流或直流滤波器设计等工作的重要手段.采用电路叠加定理说明了适用于HVDC谐波阻抗扫描的测试信号法.基于测试信号法基本原理及其在HVDC应用研究中的进展,提出测试信号法应用于HVDC谐波阻抗扫描的谐波源幅值选择方法和用于减小谐波源初相位影响的改进扫描方法.最后,以C...     

Proposed statistical performance measures for microprocessor-basedtransmission-line protective relays. I. Explanation of the statistics

The paper presents practical calculations and novel techniques for collecting performance data from protective relays. The methods are focused on, but not limited to, microprocessor-based transmission line relaying systems. Standard definitions are presented for availability, dependability, security, hardware MTBF, relaying MTBF, repair time, and other measures of interest for specific relay types. The paper explains the novel concept of exposures, the key to a standardized security measure. With these standard measures, relay users will be able to compile the first consistent industry-wide data base for relay performance assessment