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.     

Analysis of electromagnetic processes in a homogeneous long line

Dependences between the currents and voltages at terminals of a homogeneous long line were analyzed. They make it possible to more correctly explain the changes in current and voltage in an electric-traction network when switching the thyristor arms of a rectifier–inverter converter than do conclusions obtained during replacement of a long line with a circuit with lumped parameters. An imitation model of the homogeneous low-loss long line in the MATLAB/Simulink software environment is proposed that adequately represents the propagation of incident and reflected electromagnetic waves along the line. Transfer functions are presented that approximate the frequency dependences of the specific parameters of the equivalent rail–ground loop and the overhead catenary–ground loop calculated taking into account the increase in the resistance of the wires due to the eddy currents and the surface effect. The influence of frequency dependences of the specific electric parameters of an electric-traction network calculated by various methods on the free voltage oscillation decay on the electric locomotive pantograph obtained by modeling the electromagnetic processes in the traction substation–electric traction network–electric locomotive system is revealed.     

CO2弧焊电源主电路中RC缓冲电路设计

全桥逆变CO_2弧焊电源主电路IGBT开关动作时,在续流回路中由于负载的巨大变化及变压器的电感作用而形成电流、电压冲击,造成IGBT工作的不稳定.根据弧焊电源的工作原理设计了电弧负栽仿真模块,建立了弧焊逆变主电路仿真模型,动态地仿真了焊接过程中负载频繁突变的特点.通过仿真分析得知,在续流过程中IGBT能够理想关断轨迹的条件是续流二极管不开通.根据具体的主电路参数和电路工作的续流初始时刻以及IGBT开通时,缓冲电容放电对参数的影响,计算出合理开关轨迹下RC缓冲电路中的电阻值,根据缓冲回路电阻的功率限制和开关轨迹的要求计算缓冲电容值.试验证明了弧焊逆变主电路仿真模型的正确性、IGBT理想关断轨迹条件的合理性及RC参数设计公式的正确性.     

Dynamic processes in abnormal operating conditions of power supplies of welding electron-beam guns

The dynamic processes in power supplies of welding electron guns caused by abrupt change in the parameters of load, currents, and voltages have been considered. A mathematical model for the study of abnormal modes of power supplies that are part of the power unit of an electron-beam welding installation with regard to the mutual influence of their parameters has been proposed. Results of experimental studies of the operation of an inverter prototype have been compared with the simulation results.     

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.     

On the issue of control system adjustment of a direct current drive on the modulus optimum. Part 2

The results of simulating the most widespread variants of dc electric drives with optimum adjustments of the parameters taking into account the natural and artificial constraints of variables in MATLAB and Simulink are presented. Particular attention is given to the modes of armature current constraints, the influence of constraints on electric drive parameters, and comparative analysis of transient processes when a drive is started. It is shown that the system with a PI speed controller and a P current controller, which is adjusted to the modulus optimum has the best indices of overshooting and speed of response taking into account the artificial constraint of the armature circuit current and the natural constraint of the converter output voltage. The one-loop control system with a PI controller, also adjusted to the modulus optimum, has similar indices.     

Inverter welding set powered by three-phase mains

The electric welding set with a power of 10 kW powered by 380-V three-phase mains is described. It is shown that the total active current in a two-set inverter transformer is 1.5 times lower than in the single-set inverter of the same capacity with built-in shunted transistors. The external and amplitude performances are investigated and it is revealed that the available nonlinear segment does not prevent the use of the designed device for welding in air, CO₂, or argon environments.     

三相LCL型并网逆变器的阻抗建模及特性分析

考虑锁相环、电流调节器(含dq轴解耦系数)、LCL型滤波器等环节,并计及运行工作点,采用谐波线性化的方法建立了三相LCL型并网逆变器正、负序阻抗模型,并基于PSCAD/EMTDC对阻抗模型进行仿真验证。详细分析了锁相环、电流调节器控制参数及滤波器参数对阻抗特性的影响,结果表明：锁相环比例和积分增益对并网逆变器阻抗特性的影响主要在工频附近,而电流调节器比例和积分增益则在次同步和超同步频域均有一定的影响;锁相环和电流调节器积分增益主要影响逆变器工频附近的幅频特性和相频特性;电流调节器比例增益对逆变器正序阻抗特性的影响较大,而锁相环比例增益的影响较小。     

高速CO2焊波控逆变电源设计

以dsPIC30F6010数字信号控制器为核心,设计了波控逆变CO2焊接电源系统。详细介绍了该逆变电源的主电路、短路/燃弧判断电路和电流波形控制程序等。为了减少CO2焊短路过渡的飞溅,增加电弧的稳定性,提高焊接速度,提出将控制过程分成短路阶段和燃弧阶段分别加以控制的方案。研制的波控逆变电源,不仅控制参数多,响应速度快,而且能精确控制燃弧能量,因而可满足高速CO2焊控制的要求。     

基于ZVZCS的逆变焊/割多功能电源的研制

在阐述弧焊/切割电源基本特性的基础上,设计了一种基于移相全桥(Phase Shift-Full Bridge,简称PS-FB)零电压零电流开关(Zero Voltage Zero Current Swithing,简称ZVZCS)的逆变式弧焊/切割多功能电源;并在分析实现软开关条件的基础上,给出了主电路元器件的选取和设计原则:然后介绍了弧焊/切割工艺对电源特性的要求,以此为基础,进行了控制系统的设计;最后研制了一台10kW逆变式弧焊/切割多功能电源,其功能切换简单,实验结果验证了工作原理与设计原则的正确性;证实了PS-FB-ZVZCS适合用于弧焊/切割电源.     

A novel energy‐retaining inverter for AC arc welding machines

A novel energy‐retaining power supply for AC arc welding machines is proposed in this paper. In this kind of power supply, current‐steering diodes connected across the output chokes keep the inductor current continuous and retain the energy during the commutation period, hence reducing the commutation time to ensure a better welding performance. In addition, the stored energy can be released in the next energy transfer cycle to raise the conversion efficiency. The circuit operations and design procedures are likewise examined thoroughly. Experimental results on a prototype inverter for driving a 100‐A AC arc welding machine are recorded to validate the effectiveness of the presented scheme. Copyright © 2010 John Wiley & Sons, Ltd.     

计及风影响的潜供电弧自熄特性计算研究

风是影响潜供电弧自熄特性的重要因素,从电弧运动的角度出发,研究了计及风影响的潜供电弧自熄特性。利用链式电弧模型,分析电弧受到的电动力、空气阻力和风载荷,获得电弧运动速度控制方程,建立考虑风载荷的潜供电弧运动模型。利用电弧自熄的长度判据,提出了计算电弧自熄特性的仿真流程。通过比较电弧受到的风载荷与电动力,分析了在不同电流下风对电弧运动所起的作用,进一步探讨了风向和风速对燃弧时间及分散性的影响。最后对潜供电弧自熄时间进行了仿真计算,并与试验结果进行了比较分析,结果表明文中建立的电弧运动模型能有效计及风对潜供电弧的运动和自熄特性的影响,燃弧时间计算值与实测时间基本相符,具有实用价值。     

单电压环构网型并网逆变器暂态稳定性分析

随着电力电子化电力系统的快速发展,构网型并网逆变器作为新型电源得到了广泛关注,其中单电压环构网型并网逆变器因具有更强的小信号稳定性而在新能源并网中具有独特优势。同时,构网型并网逆变器在大扰动下呈现与同步电机不同的暂态响应,容易产生暂态失稳。针对这一问题,以单电压环构网型并网逆变器大扰动模型为基础,采用相平面图的方法分析了大扰动下功率控制环、电压控制环对逆变器的暂态作用,给出了关键控制器参数对暂态稳定性的影响,刻画了功角的暂态响应特性。同时,揭示了有功控制环、无功控制环和单电压环在暂态期间会改变功角超调量、逆变器输出电压幅值和变化率,进而影响并网逆变器的暂态稳定性。基于上述分析,给出了减小有功和无功下垂系数,增大电压积分系数和低通滤波器截止角频率的控制参数优化方法,可增强单电压环构网型并网逆变器暂态稳定性。最后,通过Matlab/Simulink仿真验证了分析的准确性与可行性。     

Dynamic Control of a Current-Source Inverter/ Double-Wound Synchronous Machine System for AC Power Supply

A novel dc-to-ac conversion system consisting of a load commutated current-source inverter, a double-wound synchronous machine, a position sensor, and a control circuit is being used increasingly as an ac power source in dc electric railway coaches. A detailed transient analysis of this dc-to-ac conversion system is presented and a new dynamic control strategy is proposed. It is shown that the proposed control not only stabilizes the output frequency and voltage of the system over a wide range of variations in the dc input voltage and/or the output load, but also secures safe commutation of thyristors in the inverter during transients.     

直流逆变式氩弧焊机的电源设计

概述了直流逆变式氩弧焊机的电源设计,介绍了其中频变压器的设计计算.     

数字控制的移相软开关脉冲MAG焊电源研制

提出了一种适合脉冲MAG焊工艺的零电压软开关电路拓扑,并对其工作机理进行了系统研究。为提高软开关弧焊电源控制的灵活性,开发了基于DSP的数字化控制系统,由软件对脉冲调制(PWM)波形进行移相控制,实现开关管的零电压开通和关断。利用DSP内部集成的PWM发生模块,通过选择合适的工作方式实现了PWM信号的直接数字化控制,从而实现了脉冲MAG焊高频逆变和低频脉冲波形调制。试验结果表明,所设计的软开关脉冲MAG焊逆变电源具有全范围的软开关能力,焊接性能好,稳定可靠。     

A method for improving the energy efficiency of an alternating current electric locomotive in the regenerative braking mode

A method for improving the power factor of an ac locomotive with the commutator motor operating in the regenerative braking mode is proposed. The method improves the control system algorithm of the power converter. The new switching method of inverter thyristors regulates the curve of the instantaneous power during the main switching. It allows reducing the period in which the energy flow passes to the locomotive, leading an increase in the average value of the instantaneous power. A “traction substation–electric traction network–locomotive in the regenerative braking mode” mathematical model is presented to verify efficiency of the method. The model consists of several interacting electric power substations, a section of electric traction grid, a locomotive power transformer, a four-zone inverter, a control system of reversible converter, and a dc circuit. The model is realized in the OrCAD software.     

A control system for dc arc furnaces for power quality improvements

The dc arc furnaces are highly disturbing loads for transmission and distribution networks. The present paper proposes and implements an ac–dc converter control system for power quality improvements taking into account both flicker levels and harmonics at the point of common coupling. Different set of parameters for the proportional–integral controller are investigated for optimizing the dc arc furnace power quality impact on the ac network. In this study both deterministic and random models of the arc furnace are considered together with different structures of the ac–dc converter unit. The proposed control system is tested on a real case application.     

Shaping of the load characteristic of a welding inverter

A computer model is used to assess the influence of the transmission coefficient and time constant of the control system on the load characteristic of a high-frequency AC welding inverter.     

An Economical Auxiliary Commutated Thyristor Three-Phase Inverter Suitable for Pulse Frequency Modulation

A new economical auxiliary impulse commutated thyristor inverter is described that is capable of providing a wide range of output ac voltage and output frequency which is useful in variable speed ac drive applications. Output voltage control is provided by a pulse frequency modulation technique, and input dc voltage to the inverter is constant and can be provided by a diode rectifier bridge. The parameters for the various circuit elements, such as commutating inductances and capacitances, di/dt limiting series thyristor inductances, and dv/dt limiting RC snubber circuits are all calculated from a dynamic simulation of a single-phase version of the inverter circuit using a software named ATOSEC I developed at the Universitédu Québec for a CDC 6400/IBM-370 computer. Experimental results obtained on a practical single-phase inverter are compared with those predicted from computer simulation and performance characteristics obtained in the case of a practical three-phase pulse frequency modulated inverter providing variable output voltage and variable output frequency are reported.