The operating characteristics of small grid-controlled hot-cathode arcs or thyratrons

The grid current required to fire a thyratron has been shown to depend theoretically upon the shape of the grid current characteristic before firing as well as upon the grid circuit constants.The three-element FG-17 and the four-element FG-95 and FG-98 thyratrons have been investigated.Anomalies where excessively large grid currents were required to start the arc, occurring below certain values of temperature and plate potential, have been found and are described in some detail.Although the argon-filled FG-98 was found to be free from temperature effects over the operating range, positive shield grid potentials introduced anomalies at low plate potentials.Even though the plate and shield potentials and the temperature were kept within the recommended optimum range, it was found that for minimum grid currents at firing the negative grid impedance of these tubes necessitated a grid resistance of 100 to 1000 megohms.     

新型动态电压恢复器在双馈风力发电机中的应用

在不对称电网故障下,采用基于同相位补偿法改进控制策略的新型动态电压恢复器（DVR）,提高双馈风力发电机（DFIG）的低电压穿越能力。通过两个改进的正负序检测器分别对网侧和机侧电压分量进行分解,消除不平衡故障下的负序分量的影响;利用四个PI控制器分别调节每一相序,注入串联电压,保证双馈风力发电机电压可以达到正常值;通过旋转这个串联电压,注入无功功率到电网中,保证系统的稳定运行,仿真结果证明了所提控制策略的有效性。     

分段层式干式变压器绕组线圈暂态过程的分析

建立了分段层式干式变压器绕组线圈冲击波过程的计算模型,计算出各单元的节点电压,并且比较了在雷电波作用下的计算波形与用Matlab仿真的真实电路波形,从而验证计算模型的正确性。     

Injuries produced by contact with electric circuits

This paper discusses the results of a series of experimental investigations that have been conducted at The Johns Hopkins University on the effects of electric shock. Rats and dogs were used as the experimental animals. They were completely anesthetized before the experiments. Studies of the effects produced by electric current upon the nervous system and upon the heart are reported. Three types of circuits were used in the work, namely, direct current, alternating current, and the discharge of an impulse generator.In the first series of experiments, the effect of voltage was studied and it was found that low voltage alternating current circuits are much more deadly than direct current circuits of the same voltage. At voltages of 1,000 and higher the reverse is the case. In this work, the importance of the size of the animal as related to the injury was definitely established, larger animals being able to withstand a greater current than those small in size.The resistance offered by a body in an electrical circuit was determined. The resistance is made up of two parts—the contact resistance, and the ohmic resistance of the body proper. The resistances offered at the contacts are of the nature of a voltage drop and are largely independent of the current flowing. The importance of contact resistances in industrial accidents is emphasized.In a second series of experiments the effect of the current path through the     

基于电流型多电平变流器的单相光伏并网系统

采用单相电流型多电平变流器作为光伏并网发电系统的电路接口,可以降低开关器件的开关频率和电流应力,同时可以使电网侧电流获得更好的谐波特性。为获取更好的谐波性能,电流型多电平逆变器部分采用POD-PWM调制,并通过直流侧电流反馈实现分流电感电流的均衡控制。最后,通过锁相环控制,使多电平逆变器输出的电流跟踪电网电压,实现并网。基于PSIM仿真环境,设计了单相五电平电流型光伏并网逆变系统,对上述方案的正确性和可行性进行了验证。     

Phase locking dynamics in 2D Josephson junction arrays with external load

Phase locking in a basic two-dimensional hybrid Josephson junction array consisting of two rows and four columns shunted by an external load is investigated, exploiting an approximation combining the ideas of harmonic balance with that of the slowly varying phase procedure. Using small ring inductances, the junction voltages within the same row oscillate nearly in-phase unless the external magnetic flux in the loops is near a multiple of a quarter of the flux quantum. Without external load we have found a stable antiphase regime where both rows carry out uniform interferometer oscillations. A stable in-phase regime, favored in an optimized radiation source, can be reached by means of an external inductive shunt for small external fields only.     

Effect of methods of demagnetization on the energy required to magnetize steel

In this investigation the first series of tests consisted of obtaining zero flux in two varieties of steel from various maximum flux values and by three different methods. B-H curves were obtained after demagnetization by the three methods and from the maximum value of these B-H curves hysteresis loops were taken.One method of demagnetizing was that suggested by the U. S. Bureau of Standards, which consists of current reversals through a magnetizing winding, in which current values are gradually reduced to zero. The second method consisted of applying a negative current of such an amount that the resultant value of flux would be such that when the current was released the flux value would go to zero. The third method was substantially the same as the second except the zero flux was approached from the direction of opposite polarity.The resultant B-H curves proved to be different from each other and to depend upon not only their origin but the previous history of the material as regards methods of demagnetization.The areas between the curves were evaluated.It was found that in cases of two of the three typical B-H curves the B-log H curves gave straight lines for part of the range involved.A second series of tests consisted of taking a set of hysteresis loops and repeating the determinations, using a greater number of steps to find if by taking a greater number of steps there might be a greater indicated energy loss. The results of this group of tests were not sufficiently definite to warrant conclusions.     

大容量电机起动电压质量控制方式研究

大容量交流异步电动机(9300kW)直接起动时能产生很大的冲击电流,导致线路电压明显下降。尤其是处于长线路末端的大容量电机,因线路压降大,电机起动时对线路电压的影响更为明显,从而其他用户负载的正常运作,产生的高次谐波甚至会危及电网安全。为控制线路电压质量,一般运用软启动装置实现大电机的起动。以大容量电机(9300kW)实例计算作电机起动时的电压控制方式简要分析研究。     

A vacuum tube amplifier for small direct voltages

A simple means for combining a small direct voltage with an alternating carrier is described. This consists of connecting the direct voltage in series with an alternating voltage of the same order of magnitude. The two are then passed through a copper oxide rectifier which suppresses one part of the cycle. The degree of suppression depends upon the magnitude of the direct voltage. The resulting fluctuating voltage can be amplified to any desired degree in a conventional amplifier.The theory for the simple case of pure resistance is worked out, with an example. The solution of the more general case with inductances is indicated.The practical circuit which has been used for the amplification of thermo-couple currents, and as a galvanometer power multiplier, is shown.     

Zero dynamics and funnel control for linear electrical circuits

We consider electrical circuits containing linear resistances, capacitances and inductances. The circuits can be described by differential-algebraic input–output systems, where the input consists of voltages of voltage sources and currents of current sources and the output consists of currents of voltage sources and voltages of current sources. We generalize a characterization of asymptotic stability of the circuit and give sufficient topological criteria for its invariant zeros being located in the open left half-plane. We show that asymptotic stability of the zero dynamics can be characterized by means of the interconnectivity of the circuit and that it implies that the circuit is high-gain stabilizable with any positive high-gain factor. Thereafter we consider the output regulation problem for electrical circuits by funnel control. We show that for circuits with asymptotically stable zero dynamics, the funnel controller achieves tracking of a class of reference signals within a pre-specified funnel; this means in particular that the transient behavior of the output error can be prescribed and the funnel controller does neither incorporate any internal model for the reference signals nor any identification mechanism, it is simple in its design. The results are illustrated by a simulation of a discretized transmission line.     

VCO sweep-rate limit for a phase-lock loop

Phase-lock loops (PLLs) serve important roles in phase-lock receivers, coherent transponders, and similar applications. For many of these uses, the bandwidth of the loop must be kept small to limit the detrimental influence of noise, and this requirement makes the natural PLL pull-in phenomenon too slow and/or unreliable. For each such case, the phase-lock acquisition process can be aided by the application of an external sweep voltage to the loop voltage controlled oscillators (VCOs). The goal is to have the applied sweep voltage rapidly decrease the closed-loop frequency error to a point where phase lock occurs quickly. For a second-order loop containing a perfect integrator loop filter, there is a maximum VCO sweep-rate magnitude, denoted here as R_m rad/s², for which phase lock is guaranteed. If the applied VCO sweep rate is less than R_m, the loop cannot sweep past a stable phase-lock point, and it will phase lock. On the other hand, for an applied sweep-rate magnitude that is greater than R_m, the PLL may sweep past a lock point and fail to phase lock. In the existing PLL literature, only a trial-and-error approach has been described for estimating R_m, given values of loop damping factor ζ and natural frequency ω_n. Furthermore, no plots exist of computed versus ζ and versus ζ (B_L denotes loop-noise bandwidth). These deficiencies are dealt with in this paper. A new iterative numerical technique is given that converges to the maximum sweep-rate magnitude R_m. It is used to generate data for plots of and versus ζ, the likes of which have never appeared before in the PLL literature.     

Programmable and on-demand drug release using electrical stimulation

Recent advancement in microfabrication has enabled the implementation of implantable drug delivery devices with precise drug administration and fast release rates at specific locations. This article presents a membrane-based drug delivery device, which can be electrically stimulated to release drugs on demand with a fast release rate. Hydrogels with ionic model drugs are sealed in a cylindrical reservoir with a separation membrane. Electrokinetic forces are then utilized to drive ionic drug molecules from the hydrogels into surrounding bulk solutions. The drug release profiles of a model drug show that release rates from the device can be electrically controlled by adjusting the stimulated voltage. When a square voltage wave is applied, the device can be quickly switched between on and off to achieve pulsatile release. The drug dose released is then determined by the duration and amplitude of the applied voltages. In addition, successive on/off cycles can be programmed in the voltage waveforms to generate consistent and repeatable drug release pulses for on-demand drug delivery.     

Suppression of DC-link voltage unbalance in three-level neutral-point clamped converters

Two different control approaches for suppressing DC-link voltage unbalance in Three-Level Neutral-Point Clamped Converters (NPCs) are presented in this paper. They both guarantee DC-link voltage equalization over any NPC operating conditions, i.e. when the NPC feeds or is supplied by the main AC grid at different active and/or reactive power rates. The proposed control approaches consist of either a hysteresis or a proportional regulator, each of which synthesizes the most suitable control action based on the actual DC-link voltage unbalance. Particularly, two different PWM techniques have been developed in order to achieve DC-link voltage equalization successfully, preserving NPC voltage and current waveforms at the same time. The performances achievable by means of both the proposed control approaches have been compared to each other through an extensive simulation study in order to highlight their most important advantages and drawbacks, as well as their effectiveness over any operating conditions. Particularly, both control approaches are validated in the Matlab-Simulink environment referring to DC-link voltage equalization of an NPC that represents the point of common coupling between a DC microgrid and the main AC grid.     

基于定量与定性相结合的电网低碳评价方法研究

低碳发展成为应对全球气候变暖、实现经济可持续发展的主要途径。作为碳排放主要领域之一的电力行业来说,对电网低碳水平进行综合评价既可使电网企业对当前自身的低碳发展水平拥有直观判断,也为国家在电力行业制定相关低碳政策提供方向。本文在已有研究的基础上,将各种智能电网技术的应用程度和影响电网碳排放的相关要素作为评价依据,构建了一套综合性较强的电网低碳指标体系。同时,针对当前对于电网的低碳评价注重定量分析而缺乏定性分析的问题,提出了基于改进的超效率数据包络分析模型和模糊综合评价法,实现对电网低碳水平的定量与定性分析。利用部分地区电网作为研究对象,进行算例分析,验证了方法的实用性和有效性。     

Topological interpretation of the inverse connection matrix A.sb

This paper discusses a new algebraic model of electrical networks by which a deeper understanding is achieved of the interrelation existing between a system of independent cut sets and the corresponding system of independent “contours”, in the sense of orthogonal network theory (1).The new model allows, by a redefinition of f-cut sets, to give an interpretation in terms of linear graph theory to the inverse connection matrix A^.s_b, i.e. to the transformation matrix between voltages in the orthogonal and the primitive reference frames, for a general choice of independent contours.Furthermore, a directly algebraic derivation of the voltage transformation is presented, recalling the properties of dual vector spaces and without invoking the principle of invariance of the instantaneous power.     

带隔离变压器的Cuk型有源功率因数校正的研究与设计

随着电力电子技术的发展,各种电力电子设备应用于电网,给电网带来谐波问题,各种谐波滤波器也应运而生,但这只是一种先污染后治理的被动办法,APFC是一种主动的办法,它用于开关电源前级整流器,输入电流为正弦波,不对电网产生污染。全文围绕一种新颖的基于隔离型Cuk变换器的有源功率因数校正电路的设计,从Cuk变换器的基本单元入手,分析了Cuk变换器的工作原理,在此基础上,确定了基于隔离型Cuk变换器APFC电路的基本拓扑。     

基于TL494PWM控制的电动车开关电源设计

电动自行车一般由铅酸蓄电池供电,有24V、36V和48V三种规格,但电动车的照明灯、音响、防盗报警器、里程速度显示,电机控制器一般只需12V的直流电压,文章介绍一种基于芯片TL494PWM技术的降压式DC-DC开关电源,通过闭环控制使输出电压稳定,系统具有的过流保护及使系统稳定工作的相位补偿设计都有较好的效果。     

浅谈农网升级改造电力工程监理工作

农村电网改造升级工程是一项惠民工程,随着社会的发展,农村生产力和生活水平的提高,生产、生活用电负荷的不断增加,必须要有能提供其荷载的电力设施。文章对目前农村电网改造升级工程情况进行了简单介绍,分析了现在农村电网改造升级工程中存在的问题,对农村电网改造升级工程监理工作提出了几点建议。     

配电线路微机保护软件系统设计

文中介绍了配电线路微机保护装置软件系统的总体结构及各功能模块的算法流程图。该系统能够完成线路的单相接地短路保护以及相间短路的电流速断保护和反时限过电流保护；并能够实现单相接地时线路故障点和故障类型的自动判断，便于线路的检修维护。该系统的应用将会大大提高广大城乡电网和工业企业配电网的保护水平．     

2005年3月10～12日嘉兴市寒潮大雪成因浅析

分析2005年3月10～12日嘉兴市寒潮、大雪天气过程发现:强寒潮是由乌拉尔阻高东移南垮引起强冷空气南下和前期明显回温共同造成的。500 hPa南支槽前的西南暖湿气流为大雪天气提供了源源不断的水汽;物理量诊断显示,高层辐散、低层辐合和弱的不稳定能量,为大雪的产生提供了动力抬升条件;高空西南暖湿气流突然加强,近地面层有大片逆温层存在,是预报大雪的关键,为今后预报大雪起到了一定参考的作用。