Transient processes in welding inverter for alternating current

For the widespread application of power transistors in welding invertors, a serious investigation of transient processes in the circuits of these converters is necessary in order to ensure their high reliability. The article describes an investigation in a PSIM environment for a circuit model of the welding inverter for an alternating current in the kilohertz range in various operation modes. A comparison of the modeling and experimental data for a physical model reveals their satisfactory agreement.     

New class of welding inverters

Results of theoretical and experimental investigations of a new type of a welding inverter, namely, an ac inverter welding apparatus with a frequency of 25?C50 kHz, are given. A schematic circuit of the inverter power part is described, and recommendations of enhancing the safety of operation modes are given.     

Transient effects in application of PWM inverters to inductionmotors

Standard squirrel cage induction (SCI) motors are subjected to nonsinusoidal wave-shapes when supplied from adjustable-frequency inverters. In addition to causing increased heating, these wave patterns can be destructive to the insulation. In particular, pulse-width-modulated (PWM) inverter output amplitudes and risetimes are investigated. Motor insulation capabilities are discussed. Voltage reflections are simulated for various cable lengths and risetimes and are presented graphically. Simulations confirm potential problems with long cables and short risetimes. Application precautions are also suggested     

Simulation of transient processes in the welding inverter

The skew half-bridge scheme in the commuting mode of the welding arc is simulated in a PSIM environment. An examination of the physical model proves the convergence of the applied mathematical model.     

单相光伏并网逆变器共模电流的分析与抑制

单相非隔离型光伏并网逆变器由于缺少变压器的电气隔离,工作时常会产生较大的共模电流,即漏电流。为此,在分析了共模电流产生原因的基础上,研究了几种能够有效抑制共模电流的拓扑结构,分别为带交流旁路的全桥拓扑、带直流旁路的全桥拓扑、H5拓扑以及H6拓扑。其抑制共模电流的基本原理为通过相应的开关调制模式,使系统寄生电容上的共模电压保持恒定,从而减少共模电流的产生,最后仿真结果验证了这几种拓扑结构的可行性。由于不同拓扑结构所含功率器件数量的不同以及调制模式的不同,系统的工作效率有所差异,对比发现H5、H6拓扑优于其他拓扑。     

Hydrogen energy sources with current inverters in ship AC power plants

The use of hydrogen energy sources is promising for the creation of ship electric-power systems. These sources have a number of significant advantages over conventional energy sources (diesel generators or turbine generators), such as the possibility to provide low-noise regimes of ship motion and creation of an airindependent shipboard power plant. Using hydrogen energy sources as components of electric-power systems along with conventional energy sources makes it possible to optimize the operation of diesel generators as regards minimum fuel consumption and provide a reserve of power. The article analyzes the structural variants of energy channels with hydrogen energy sources and current inverters providing parallel operation with diesel generators or turbine generators in ship ac electric-power plants. The problems of regulation and distribution of active and reactive powers between sources operating under a total load are considered. Comparative analysis of the generalized energy indicators and of the degree of distorting influence of energy channels with hydrogen energy sources on the voltage waveform of a ship electrical-power network in static operating modes is presented.     

Transient analysis of an advanced static var compensator using quad-series voltage-source PAM inverters

This paper deals with an advanced static Var compensator (ASVC) using quad-series voltage-source PAM inverters. The ASVC consists of four three-phase voltage-source inverters with a common dc capacitor and four three-phase transformers, each primary winding of which is connected in series with each other. Each inverter outputs a square-wave voltage, while the synthesized output voltage of the ASVC has a 24-step wave shape. This results not only in a great reduction of harmonic currents and dc voltage ripples but also in fewer switching and snubbing losses. In this paper, transient analysis is performed with the focus on the response of reactive power and the resonance between the dc capacitor and ac reactors. Experimental results obtained from a small-rated laboratory model of 10 kVA are also shown to verify analytical results based on the p-q transformation. The analytical results help in the design of system parameters such as the capacity of the dc capacitor and feedback gains.     

Transient stability index for online stability assessment and contingency evaluation

An online methodology is proposed for assessing the robustness of a power system from the point of view of transient stability, and a scalar expression, the transient stability index, is accordingly derived. The reliability and sensitivity of this index are tested by means of simulations for a number of power system cases. The index is shown to be appropriate for online stability assessment, contingency evaluation and preventive control.     

计及寄生电容和纹波电流的电压源型逆变器死区效应与补偿方法

电压源型逆变器中固有的死区效应降低了输出电压的品质。为了精确补偿死区效应,需要建立死区效应导致的逆变器输出电压失真的精确模型。但是,已有死区效应模型没有考虑开关管等效并联电容和电感电流纹波对于死区效应的影响,导致死区补偿结果难以优化。本文通过详细分析和推导,发现寄生电容和纹波电流会影响输出电压的精度,并给出了输出电压误差的精确数学表达式。在此基础上,本文提出一种在线、自适应的死区精确补偿方法。最后,通过仿真和实验证明了本文分析的正确性和死区补偿方法的有效性。     

Single current sensor technique in the DC link of three-phasePWM-VS inverters: a review and a novel solution

A review of the existing methods to determine the output currents in a pulsewidth modulation voltage-source (PWM-VS) inverter using a single current sensor in the DC link is presented, and a novel solution is proposed. The unique arrangement of the DC link allows full protection of the inverter from short circuits and overloads. Also, a new method of sampling the DC-link current is described that produces true values of the output currents at the centers of switching intervals. Results of investigation of an experimental setup have shown that full protection of the inverter has been accomplished and the output currents can accurately be determined within the whole operating area     

并联逆变器馈电PMSM调速系统谐波和环流控制

针对大功率场合下并联逆变器馈电永磁同步电机( PMSM)调速系统中存在的环流问题和电机电流谐波性能差的问题,提出一种并联逆变器馈电永磁同步电机控制策略来协调控制不同并联逆变器模块实现电机总电流波形优化,并有效地抑制并联逆变器模块间环流。分析并联逆变器馈电PMSM调速系统的电路结构及并联逆变器环流的等效电路模型,提出针对并联逆变器PMSM调速系统的移相空间矢量脉宽调制( SVPWM)技术和随机SVPWM技术,并通过在SVPWM中动态分配零矢量作用时间来抑制各逆变器模块间的环流。仿真和实验结果均验证了所提出的控制策略的有效性,采用移相SVPWM和随机SVPWM策略可改善电机电流的谐波性能,采用环流抑制环节后可以有效地消除电路中的环流。     

Transient stability hierarchical control in multimachine powersystems

The authors present the optimal transient stability control problem in a hierarchical structure for multimachine power systems. The two-level structure retains the local closed-loop controls, thereby easing its implementation on existing systems. The formulation accounts for nonlinearities and interconnections, and the optimization of the system transient performance is obtained with less computational effort. Since the computations are distributed among the many local feedback subsystems, the storage and solution times are considerably less than those required by a single overall centralized controller. This advantage becomes much stronger as the system size increases. For illustration purposes, this technique was applied successfully to a four-machine system     

短路电流对高压断路器及其开断电流选择的影响

论述了高压断路器在开断短路电流时,短路电流对高压断路器的影响,归纳总结了短路开断计算时间及非周期分量百分数的估算方法．并提出如何根据短路电流合理选择高压断路器的额定开断电流。     

Transient stability enhancement and voltage regulation of powersystems

Improvement of the transient stability and voltage regulation of a single-machine-infinite-bus power system under the effects of a symmetrical three-phase short-circuit fault is detailed. The dynamical model of the system is described. A design strategy for nonlinear controllers is considered, and the design of a nonlinear variable-structure excitation controller is described. Simulation results obtained using the nonlinear excitation controller are given, and a new nonlinear coordinated controller is proposed. Simulation results obtained by using the nonlinear coordinated controller are presented     

空间太阳电池焊接影响因素研究

空间太阳电池阵的互连是通过将太阳电池电极与其紧贴的银箔互连片焊接来完成,该焊接采用平行间隙电阻焊技术,主要从焊接参数、焊接模式、电极状态、互连片状态等方面对影响空间太阳电池焊接的因素进行研究,并提出对应措施,以提高焊接的稳定性和可靠性.     

Transient stability output margin estimation based on the energy function method

In this paper, a new method of estimating the critical generation margin (CGM) in power systems is proposed based on transient stability diagnostics. The proposed method can directly compute the stability limit output for a given fault based on the transient energy function method (TEF). Since CGM can be directly obtained by the limit output using estimated P‐θ curves and is easy to understand, it is more useful than the conventional critical clearing time (CCT) of the energy function method. The proposed method can also estimate CGM as a negative value, which means instability in the present load profile, and so a negative CGM can be directly used as a restriction on generator output. The accuracy and fast solution ability of the proposed method are verified by applying it to a simple 3‐machine model and IEEJ EAST10‐machine standard model. Furthermore, the usefulness of the method for severity ranking of transient stability for various fault cases is discussed by using CGM. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 10–19, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.21035     

Transient current distribution in a sphere by feeding a current on the surface from a loop of arbitrary shape

Contents  The complete electromagnetic field of an arbitrary transient current distribution in a sphere can be represented by a superposition of a transverse electric and a transverse magnetic field. In this paper, the transient current distribution in a permeable and conducting hollow sphere is calculated for an exciting current of arbitrary time dependence which is fed into the sphere via the surface from an open loop of arbitrary shape. The original configuration is separated into two characteristic configurations whose current distributions are derived from a transverse electric and a transverse magnetic second order potential. The transverse magnetic field is determined by the position of the feeding points on the surface of the sphere. The transverse electric field is influenced only by the contour of the exciting loop in the nonconducting space. If the exciting loop is closed outside the hollow sphere, the transverse magnetic field vanishes and the solution for the transverse electric field can be used to describe the shielding of the transient electromagnetic field by a spherical screen. The general transient solution is proved for the special case of a sinusoidal time dependence and compared with the direct solution of the differential equation for the complex amplitudes of field quantities. An energy balance is introduced which describes the energy flow during the transient process. Received: 18 October 2000     

Improved current control technique of VSI PWM inverters withconstant modulation frequency and extended voltage range

A hysteresis control method for three-phase, current-controlled, VSI PWM (pulse width modulation) inverters characterized by constant switching frequency is presented. The method is based on substantial improvement of the principle of minimization of interference among modulations of the various phases, which does not require any knowledge of load parameters or EMF, provided the load is symmetric. Interference minimization allows PLL (phase-locked loop) control of switching frequency. The inherent benefits of the proposed technique are full exploitation of inverter voltage capabilities and a definite reduction ion commutation losses. The method minimizes commutation losses and current ripple while allowing maximum output AC voltage to be obtained from the inverter. The method exhibits all the favorable characteristics of hysteresis controls: fast response, good accuracy, and robustness. Experimental tests confirmed theoretical forecasts, showing excellent performance of the control     

当前电焊机行业经济运行分析报告

2008年电焊机行业在经济不稳定的大环境下稳步发展,行业综合实力进一步增强,新产品产值增长迅速,技术创新成效显著,产品结构调整取得突破性进展。企业应通过自主创新掌握先进的设计技术和制造技术,提高自身的核心竞争力,还应根据自己的特点,向小而专、小而特、小而强的方向发展。