Stabilized 400 to 3600 c/s magnetic frequency multiplier

This paper presents detailed design information and performance characteristics of a stabilized 400 to 3600 c/s frequency transformer of the phase multiplier type. The described three-phase-operated prototype design provides a maximum output power of 40 watts. The performance is such that, with output power values up to about 20 watts, actual variations of the 3600 c/s output voltage are ±0.1 to 0.3 percent, although the 400 c/s supply voltage may be changed within the wide range of 80 to 220 volts. As a result of the application of square-loop core material (Orthonol 2-mil tape cores), the waveform of the square-wave output voltage is similar to that of a switching transistor magnetic core multivibrator. Since the output terminals can be permanently short-circuited, the frequency multiplier protects itself and the equipment it supplies from overloads. In view of these properties, the described prototype design will be valuable for those applications in control engineering, where simplicity, ruggedness, extreme reliability, and almost unlimited life, are of prime importance.     

Design and control of single-phase dynamic voltage restorer

Dynamic voltage restorer (DVR) is a custom power device used in electrical distribution system for power quality improvement. It ensures regulated voltage supply to the sensitive loads, even in case of voltage sag and swell disturbances in the distribution network. It is a series connected device and compensates voltage sag and swell by injecting a voltage with the help of a series transformer. The injection of an appropriate voltage component in the event of a voltage disturbance requires a certain amount of real and reactive power. Conventionally, DVR consists of an energy storage device, which supplies the required power over the limited duration of the sags. Large magnitude and long duration of sags lead to heavy financial investment in energy storage unit. To overcome this limitation, a single-phase back-to-back converter-based DVR is implemented in this work, which eliminates energy storage requirement. The integration of series and shunt converter makes the DVR capable of bidirectional flow of energy. Therefore, the key advantage of this topology is its capability to compensate for long-term voltage sag and swell. Modelling of the DVR and its controller design is included in this paper. The effectiveness of control schemes, protection schemes and starting sequence of operation of DVR is verified through detailed simulation studies. A scaled down laboratory prototype of DVR is developed. The viability of these schemes is confirmed by the experimental results generated from the laboratory prototype. Various challenges faced during the prototype development and corresponding solutions are also discussed in this paper.     

一种汽油变频发电机组中的辅助直流电源设计

针对汽油变频发电机组中逆变器所需多组低压直流电源问题,设计了一种多路输出的开关辅助电源, 结构简单紧凑、输出电压纹波小、体积小、成本低;通过分析高频变压器的设计原理,设计了一台功率为１５W 的四路直流输出的开关辅助电源;实验证明了该辅助电源的可行性。     

Single phase 1-kVA amorphous core transformer: design, experimentaltests, and performance after annealing

The design and experimental implementation of a single-phase power transformer operating at 1 kVA, 110/220 V, and 60 Hz, with an amorphous alloy core are described. The prototype core material is annealed in an argon atmosphere, under a DC magnetic field applied along the ribbon length. The experimental results are presented to compare the amorphous core transformer performance with another transformer with the same rated power, but with a silicon steel core     

测试仪器缓冲技术及平台研究

测试仪器缓冲平台研究的目的是在船舶进行冲击试验过程中为测试仪器提供冲击防护、可靠稳定的电源环境以及便捷的操作空间。测试仪器缓冲平台由FD40-10型空气弹簧和聚氨脂阻尼块串联支撑的弹性平台,平台根据船电的特殊情况配置隔离变压器及UPS大功率不间断电源。通过理论分析、试验室试验以及原型样机的冲击试验,证明测试仪器缓冲平台能够确保在大量级冲击环境下测试数据的可靠获取。     

High-performance light emitting diode backlight driving system for large-screen liquid crystal display

A high-performance light emitting diode backlight driving system is proposed for large-screen liquid crystal display. The proposed system consists of a boost converter for power factor correction (PFC) and an active-clamp converter for dc-dc power conversion. With coupled inductors and simple passive components, the proposed PFC circuit minimises the switching losses by reducing the reverse-recovery current. The active-clamp converter operates under zero-voltage switching for the power switches and its output rectifier is composed of a current doubler and a synchronous rectifier for reducing conduction loss. The proposed backlight driving system is analysed and its design consideration is discussed in detail. Experimental results for a 300 W (3.3 V/90 A) prototype at a constant switching frequency of 100 kHz are presented to verify the analysis and the performance of the proposed system.     

Implementation of a low-power electronic tap-changer in transformers

The criteria for optimal configuration of transformer windings as well as power electronics switches are proposed for the design and implementation of a low-power electronics tap-changer. The aims of this optimisation include minimisation of: 1) number of switches and their voltages and currents, 2) number of taps in the transformer, 3) deviation of the amplitude of voltage compared with the reference voltage in the regulation bus and finally increasing number of voltage steps. The hardware for designing and manufacturing a prototype electronic tap-changer is described. The test results for this prototype are presented which shows the advantages of the proposed tap-changer over a mechanical tap-changer.     

A passive auxiliary circuit with interphase transformer applied in 12-pulse converters to provide clean power utility interface

This paper proposes a passive auxiliary circuit which can be added to an interphase transformer (PAC + IPT) configuration to reduce the total harmonic distortion (THD) existing in 12-pulse diode rectifier converter systems at AC mains. The proposed PAC + IPT compensation method is a simple structure, with low power consumption and requires no extra DC power supply. We present the theoretical analysis of the proposed topology that lessens the total harmonic distortion (THD) and evaluate the dynamic simulation results on a 12-pulse converter system and a 3-kW laboratory prototype. Both the simulation and the experimental results show that the proposed PAC + IPT compensation method can improve the power quality and provide a clean power utility interface of AC line input currents for a conventional 12-pulse diode rectifier converter.     

Power Transformers Internal Insulation Design Improvements Using Electric Field Analysis Through Finite-Element Methods

Understanding the potential and electric field distribution in the insulation system of a transformer during transients is vital to its construction. Therefore, we have developed a method for electric field analysis inside a power transformer. The method consists of the following steps. (1) A lumped parameter equivalent model is constructed by dividing transformer windings into several blocks. (2) The electric circuit parameters of this model are calculated. (3) Employing the results of the transformer transient model analysis as boundary conditions, a 2-D asymmetrical electric field finite-element analysis is performed to determine electric fields through the windings. The method has been examined employing power frequency and impulse voltages. We have also demonstrated successful application of the method to a transformer and have verified the computed results by comparison with measured results.     

Design and identification of an equivalent circuit for an LCT component: inventory and representation of losses

A new kind of passive component, the LCT [integrated inductor (L), capacitor (C), and transformer (T)] is becoming very fashionable in the switch mode power supply area. Starting from our knowledge in transformer characterization, we recently elaborated an equivalent circuit for this component. This equivalent circuit is fully deducible from impedance measurements. No dismounting of the component is needed, and no information about its internal design is required. This paper aims mainly to present the new equivalent circuit and the method leading to its identification using a commercial impedance analyzer. The LCT intended to a 300-W power supply working at 200 kHz has been built and characterized between 100 Hz and 40 MHz. Analyzing the frequency dependence of the real part of serial and parallel impedances, several kind of losses rarely taken into account have been identified. Among these losses are those related to the capacitor insulator and those due to the dielectric constant of Mn-Zn ferrite core. Equivalent circuits are supplied to represent every type of loss, and their accuracy is checked.     

High power universal piezoelectric transformer.

This study describes a multilayer piezoelectric voltage and power transformer that has one direction poling, operates in a wide-frequency range and delivers both step-up and step-down voltages by inverting the electrical connections. In this design, the input and output electrodes are on the same side of the disk and are isolated from each other by a fixed isolation gap. The electrode pattern is a ring/dot structure such that it uses radial mode for both input and output part that are built-in on the same ceramic disk. A prototype transformer was fabricated of size 15 x 2.78 mm2 having mass of 3.8 gm. In the step-down configuration at the constant output power of 6 W, the transformer characteristics across a 100 ohms load were found to be efficiency = 92%, gain = 0.21 input voltage = 110 Vrms, and temperature rise = 20 degrees C from the room temperature. In the step-up configuration at the constant output power of 5 W, the transformer characteristics across a 5 kohms load were found to be efficiency = 97%, gain = 9.5, input voltage = 16 Vrms, and temperature rise = 8 degrees C from the room temperature. A detailed equivalent circuit analysis of the transformer was done, and the results were found to be in excellent agreement with the experimental results.     

High power universal piezoelectric transformer

This study describes a multilayer piezoelectric voltage and power transformer that has one direction poling, operates in a wide-frequency range and delivers both step-up and step-down voltages by inverting the electrical connections. In this design, the input and output electrodes are on the same side of the disk and are isolated from each other by a fixed isolation gap. The electrode pattern is a ring/dot structure such that it uses radial mode for both input and output part that are built-in on the same ceramic disk. A prototype transformer was fabricated of size 15 x 2.78 mm2 having mass of 3.8 gm. In the step-down configuration at the constant output power of 6 W, the transformer characteristics across a 100 omega load were found to be efficiency = 92%, gain = 0.21 input voltage = 110 V(rms), and temperature rise = 20 degrees C from the room temperature. In the step-up configuration at the constant output power of 5 W, the transformer characteristics across a 5 komega load were found to be efficiency = 97%, gain = 9.5, input voltage = 16 V(rms), and temperature rise = 8 degrees C from the room temperature. A detailed equivalent circuit analysis of the transformer was done, and the results were found to be in excellent agreement with the experimental results.     

Predicting total harmonic distortion in asymmetric digital subscriber line transformers by simulation

As a design application, the asymmetric digital subscriber line (ADSL) broad-band line transformer offers somewhat different challenges than those in power supply design. In this paper, we use simulation to analyze total harmonic distortion (THD) as affected by the nonlinear behavior of the magnetic material in a line transformer. We use a mixed-technology model of the line transformer and circuit simulation to predict the level of THD for a variety of core types and configurations. A comparison of the simulation results with measured THD figures demonstrates the accuracy of the models.     

A novel four-quadrant power supply for low-energy correction magnets

This paper describes an efficient power supply to feed low-energy correction magnets in particle accelerator applications, where a controlled current with trapezoidal profile and four-quadrant operation is needed. The selected design is based on an AC–DC matrix converter topology, which uses the Space Vector Modulation (SVM) technique to obtain a near unity power factor at the AC input and output DC current regulation. This topology allows performing high-frequency isolation, while four-quadrant operation is maintained, and reducing volume and weight as compared with the classical thyristor (SCR)-based technology. Control tasks are implemented on an all-digital control card: output current regulation is accomplished in a digital signal processor device and SVM is implemented in a Field-Programmable Gate-Array. Simulations and experimental results of a 1.2 kW prototype validate the design.     

敏感用户高品质交-直流级联供电方案研究

工业过程中大量使用的变频器(variable frequency drive,VFD)在采用传统交流供电时易受到电压暂降影响,传统治理方式存在检测延时、控制复杂等问题。为此,该文从敏感负荷变频器在电网扰动工况下的供电需求量化出发,围绕供电拓扑设计、DC/DC变换器的控制策略及储能单元容量配置等方面,构建一种实用化工业用交-直流级联供电方案。该文利用电压暂降过程中直流供电回路与敏感负荷间的压差自感应控制,实现交-直流供电回路无扰动切换,提高电压暂降治理响应的快速性;采用两相交错并联DC/DC变换器接入集中式储能,减少储能系统纹波系数,并给出两相均流控制方法。最后,通过Matlab/Simulink中的建模仿真与样机的实验测试,验证所提方案能够在交流系统发生不同严重程度电压暂降过程中为各类敏感负荷提供稳定的连续供电,为解决工业敏感用户高品质供电问题提供可实用的新思路。     

牵引变压器模糊故障诊断技术

牵引变压器是牵引供电系统的重要组成部分之一，对其DGA成分和含量进行在线监测并进行故障判断，能有效地提高电气化铁路运行可靠性。目前对变压器的故障性质判断大多是根据IEC三比值法进行的。而实践中，一些DGA结果与已存在的IEC编码不符，或造成缺码现象。论文采用模糊三比值诊断法进行故障性质判断能有效地解决这一问题。     

Inductive coupler for contactless power transmission

To provide power to a moving vehicle without using contacts, a transformer is presented, consisting of a fixed primary winding inductively coupled to a moving secondary winding. The primary winding along the whole trajectory of motion is configured such that its magnetic stray field and its self inductance are limited. This winding transfers power to the moving coupler containing the yoke and the secondary winding. The secondary winding is a resonant circuit, with a rectifier and the motor of the vehicle as load. To describe the energy transmission system, a numerical model is developed that combines an electrical circuit with a 2D nonlinear finite element model. This model is used for an optimisation of the design. For the optimised configuration, an experimental setup is built to validate the model by measurements. A sensitivity analysis is carried out concerning the primary current, the supply frequency, the position of the secondary winding relative to the primary winding and the number of vehicles coupled with the primary winding.     

牵引变压器绝缘在线监测技术研究

牵引变压器是牵引供电系统的重要组成部分之一,监测牵引变压器运行状态,及时地发现牵引变压器内部故障,对于确保高速铁路安全运行具有重要的意义。DGA技术是检测变压器潜伏性绝缘故障的有效措施之一。文章基于DSP技术,设计了一套牵引变压器DGA在线监测系统,经过实验室多次模拟试验,系统数据理想可靠。     

Analysis and implementation of soft switching converter with series-connected transformers

The system analysis and design consideration of a zero voltage switching (ZVS) converter with series-connected transformers are presested. Based on the operational behaviour, each transformer in the adopted converter can be operated as an inductor or a transformer. Therefore no output filter inductor is needed in the adopted converter. To reduce the voltage stress of the switching device in the conventional forward converter, an active snubber based on a clamp switch and a clamp capacitor is used to recycle the energy stored in the transformer leakage. During the transition interval, the resonance based on the junction capacitance of switches and transformer leakage inductance can achieve ZVS operation of switches. The centre-tapped rectifier is used at the secondary side to achieve full-wave rectification. The operating principles, steady-state analysis and design equations of the proposed converter are provided. Finally, experimental results for a 100 W (5 V/20 A) prototype circuit are provided to verify the converter performance.     

基于解析小波变换的变压器绕组模态参数识别

电力变压器绕组的模态参数与绕组结构振动特性、动力特性优化设计及振动故障诊断密切相关,考虑到传统的模态识别方法在获取变压器绕组这类非线性系统参数时的局限性,在对某10 kV实体变压器绕组进行轴向激振实验的基础上,引入复小波变换法对测试得到的振动信号进行分析,同时使用Crazy Climber算法提取小波脊线,得到变压器绕组的前三阶固有频率及其对应的阻尼比。计算结果与目前通用的频域识别方法Poly Max法识别结果的良好吻合说明计算结果的正确性。此外,计算结果表明基于小波变换的模态参数识别方法具有较强的抗干扰性能力,适合于分析变压器绕组这类复杂结果的模态参数。