Criterion of Magnetic Saturation and Simulation of Nonlinear Magnetization for a Linear Multi-core Pulse Transformer

The linear multi-core pulse transformer is an important primary driving source used in pulsed power apparatus for the production of dense plasma owing to its compact, relatively low-cost and easy-to-handle characteristics. The evaluation of the magnetic saturation of the transformer cores is essential to the transformer design, because the energy transfer efficiency of the transformer will degrade significantly after magnetic saturation. This work proposes analytical formulas of the criterion of magnetic saturation for the cores when the transformer drives practical loads. Furthermore, an electric circuit model based on a dependent source treatment for simulating the electric behavior of the cores related to their nonlinear magnetization is developed using the initial magnetization curve of the cores. The numerical simulation with the model is used to evaluate the validity of the criterion. Both the criterion and the model are found to be in agreement with the experimental data.

Finite Element CAD Experiments on the Effect of Magnetic Loss in Power Transformers with Laminated Cores

The paper describes a simulated experiment that focuses on the numeric computation of magnetic loss in the laminated core of a single-phase power transformer. The students’ laboratory work is part of the library of experiments of the Electrical Machines virtual laboratory and makes use of the two-dimensional open-access electromagnetic field analysis software Finite Element Method Magnetics. The idea of the simulated exercise is to demonstrate how the magnetic loss caused by time-varying excitations affects the magnetic permeability, μ, of the laminated core and the terminal quantities of the energizing winding. A parametric analysis employing different values for the electrical conductivity and maximum hysteresis-induced angle of the laminated material yields five different field problems with increasing magnetic loss. Electric circuits characterized by the (I-V) operating point and reflected impedance of the energizing winding provide the information required to compute the changes in real power ΔP, reactive power ΔQ and magnetically stored energy ΔWm between successive problems characterized by increasing magnetic loss. The concept of reflected impedance helps to explain the physical meaning of the changes in power dissipation and energy storage in the laminated core.

Design of a Rogowski Coil with a Magnetic Core Used for Measurements of Nanosecond Current Pulses

A Rogowski coil is developed to detect the nanosecond pulse signals of the discharge current with a wide bandwidth of 800 kHz to 106 MHz and high sensitivity of 2.22 V/A. Performance tests show that the Rogowski coil has both excellent dynamic and static characteristics. Calibrating results and the comparison between the standard current shunt and the developed Rogowski coil for the measurement of nanosecond discharge pulses demonstrate that the developed Rogowski coil can reproduce the actual waveform of the discharge current accurately.

Magnetic flux leakage analysis and compensation of high-frequency planar insulated core transformer

A novel high-frequency and high power density planar insulated core transformer(PICT) applied to high voltage DC generator is introduced. PICT's operating principle and fundamental configuration are described,and preliminary experimental results in self-designed PICT apparatus are presented. Emphatically, magnetic leakage flux(MFL) giving rise to the output voltage drop is analyzed in detail both theoretically and by finite element method(FEM). Showing good consistency with experimental result, FEM simulation is considered to be practicable in physical design of PICT. To cancel out leakage inductance and improve the voltage uniformity,compensation capacitor is adopted and experimental verification is also presented. All shows satisfactory results.

Research of a fractional-turn ratio saturable pulse transformer and its application in a microsecond-range pulse modulator

As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is constructed and analyzed in this paper.Preliminary experimental results show that if the primary energy storage capacitors are charged to 300 V,an output voltage of about 19 kV can be obtained across the capacitor connected to the secondary windings of a fractional-tum ratio saturable pulse transformer.Theoretical and experimental results reveal that this kind of pulse transformer is not only able to integrate a step-up transformer and a magnetic switch into one device,but can also lower the saturable inductance of its secondary windings,thus leading to the relatively high step-up ratio of the pulse transformer.Meanwhile,the application of the fractional-turn ratio saturable pulse transformer in a μs range pulse modulator as a voltage step-up device and main switch is also included in this paper.The demonstrated experiments display that an output voltage with an amplitude of about 29 kV,and a 1.6 μs pulse width can be obtained across a 3500 Ω resistive load,based on a pulse modulator,if the primary energy storage capacitors are charged to 300 V.This compact fractional-turn ratio saturable pulse transformer can be applied in many other fields such as surface treatment,corona plasma generation and dielectric barrier discharge.

Nanosecond Pulse Generators Based on Magnetic Pulse Compression System

Magnetic pulse compression(MPC)system has been widely-used for over a few decades as a technique for producing short-duration,high-peak-power pulses reliably.A novel MPC system which does not contain external demagnetization circuits,has broadened the application of MPC systems.Improvements for novel MPC systems are presented.To meet the required voltage and compression gain and on considering of the overall system efficiency,two kinds of most popular MPC systems based on the improved MPC topology are designed,which are 2-stage MPC system and 3-stage MPC system,respectively.Based on the improved MPC topology,several kinds of compact pulse generators are built in pulsed power and supply technology laboratory of Institute of Electrical Engineering,Chinese Academy of Sciences.These generators illustrate that the improved MPC topology,together with solid state switches provides an ideal way to generate pulses of around 100 nano-seconds in width,with mid and high voltage of 10 kV to 100 kV,and a high repetition frequency of about 30 kHz.

Study of the Thin Film Pulse Transformer

A new thin film pulse transformer for using in ISND and model systems is fabricated by a mask sputtering process. This novel pulse transformer consists of four I-shaped CoZrRe nanometer crystal magnetic-film cores and a Cu thin film coil, deposited on the micro-crystal glass substrate directly. The thickness of thin film core is between 1 and 3 μm, and the area is between 4mm×6 mm and 12mm×6 mm. The coils provide a relatively high induce of 0.8 μm and can be well operated in a frequency range of 0.001~20 MHz.

CSR Pulsed Switching Power Supplies

In 2001, CSR power supply system made a great progress. Three prototypes were designed for CSR quadruple and correct magnet. Three different companies provided the three prototypes, but the same circuit-chopper were employed. The simplified diagram is showed in Fig.1. All pulsed switching power supply prototypes were tested successfully before the end of 2001.

Effects of Pulsed Current and Pulsed Magnetic Field Complex Pretreatment on Martensite Transformation of Cr5Steel during Continuous Cooling

Carbide precipitation and martensite transformation in Cr5 steel have been observed in situ by high-temper- ature confocal laser-scanning microscopy. In this way, the influences of pulsed current and pulsed magnetic field complex pretreatment on carbide precipitation and martensite transformation during continuous cooling have been studied. The results show that the electropulsing complex pretreatment promotes the precipitation of M7 C3-type car- bides at high temperature, increases the start and finish temperatures of martensite transformation, and extends the phase transformation time. Martensite prefers to nucleate in the austenite with less precipitation of carbides due to the chemically homogeneous distribution of solute atoms.

基于混合铁心的新型电流互感器研究

传统电流互感器铁心饱和会导致其二次电流波形发生畸变,进而可能影响电能计量的精度或引起继电保护设备错误动作,威胁电网的安全稳定运行。针对此类问题,提出了基于混合铁心的新型电流互感器(CCCT)。CCCT主要由混合铁心、二次绕组、二次电阻、磁场传感器与信号处理电路组成,其中混合铁心包含完整的内铁心与带气隙的外铁心,磁场传感器放置在外铁心的气隙中,其输出信号用于补偿发生畸变的二次电流。为验证该结构的有效性,进行了有限元仿真,制作了CCCT样机并进行了正弦交流电流、正弦半波电流、短路电流和直流电流的测量实验。有限元仿真与实验结果表明,CCCT在额定电流下的复合误差小于0.2%,稳态对称短路电流下的复合误差为2.04%,暂态短路电流下的峰值瞬时误差为4.25%,直流条件下输出与输入的拟合优度为0.999 9,既基本保留了传统电流互感器的测量精度,也具有良好的暂态响应特性与抗直流特性,可同时满足相关标准对测量、保护用电流互感器的精度要求,具备在实际工程中应用的潜力。

高频纳秒脉冲调制器的分立磁耦合驱动器设计

随着高压纳秒固态脉冲发生器在生物、工业和环境等领域的应用日益广泛和深入,脉冲波形、电压幅值、脉冲持续时间、脉冲重复频率等参数已成为特定脉冲功率应用所需的基本可控变量。为了进一步减小电源的体积、降低成本,提出一款以正极性Marx为主电路、多个脉冲变压器为核心驱动器、具有纳秒级前沿高重复频率的高压纳秒脉冲调制器。提出的驱动器结构紧凑,无需提供多路隔离供电的驱动电源,可以在高重复频率下实现两个金属氧化物半导体场效应晶体管(MOSFETs)的栅极电压快速同步上升和下降,获得百纳秒以内、幅值可控的栅极驱动电压。不仅最大脉宽不受磁芯饱和的限制,而且负偏置电压使开关管可控关断,同时在一定程度上避免了电流流过MOSFET米勒电容而引起的寄生导通,提高了电路工作的可靠性。此外,研究了不同匝数和磁芯材料对驱动波形的影响。搭建了一台14级脉冲调制器样机,测试结果表明,基于该驱动器下的调制器输出电压和脉宽都连续可调,具有改变脉冲轮廓的能力,最大输出电压可达5.5 kV,脉宽调节范围为100 ns~50 ms,最小上升时间约18 ns,重复频率为100 kHz。

基于单芯移相变压器的差动保护配置研究

移相变压器能够有效调控潮流,为保障电力系统安全可靠运行,为移相变压器配置性能优良的保护不可或缺。以某示范工程的35 kV单芯对称型移相变压器为研究对象,提出相应的本体保护方案。首先,基于基尔霍夫电流定律和电磁感应定律分析其运行特性。然后,结合其拓扑结构,设计了保护用电流互感器的安装位置,构建了电平衡差动保护和磁平衡差动保护方案。此方案可覆盖单芯移相变压器内部各绕组和绕组引线相间故障以及各绕组匝间故障。最后,基于Matlab/Simulink平台搭建单芯移相变压器模型,通过设置本体内部典型故障,验证了提出的两种差动保护配置方案的有效性。

谐波下干式变压器铁心磁场-温度场仿真分析

为了更加准确地研究干式变压器铁心磁场和温度场分布,分析不同激励对干式变压器铁心磁场损耗和热点温升的影响,首先使用Maxwell计算了干式变压器瞬态磁场分布,得到空载条件下铁心磁场损耗。在此基础上提出了一种三维干式变压器磁场-温度场耦合计算方法,将磁场损耗耦合至Fluent作为温度场计算的热源,采用流固耦合的方法计算干式变压器温度场分布,获得铁心热点温度和位置。最后,基于上述方法对谐波下变压器铁心的磁场和温度场进行计算,分析了谐波次数和谐波含有率对干式变压器铁心损耗和温升的影响。所研究内容为谐波下变压器铁心温升监测提供了参考。

脉冲激励下铁基纳米晶磁芯的Jiles-Atherton模型参数辨识及应用

通过理论分析对经典J-A方程进行了修正,增强了其在脉冲条件下的适应性,利用脉冲磁化特性实验平台,测量了铁基纳米晶磁芯在不同磁化速率下的磁滞回线,采用遗传算法进行脉冲激励下的J-A参数辨识,将算法模拟的磁滞回线与实验测试的磁滞回线数据集进行拟合,验证了修正后的J-A方程的有效性,最后将遗传算法寻优得到的J-A参数应用于脉冲变压器场路耦合模型的磁芯J-A参数定义中,分析脉冲变压器初级电压为1.5 kV时的仿真与实验误差,得到脉冲变压器输出波形的脉冲前沿误差为3.33%,幅值误差为2.91%,相比于J-A参数的常规非线性求解方法精度更高,能更好地应用于脉冲功率系统中含磁性元件的建模仿真。

固态LTD的脉宽叠加技术仿真

针对脉冲电磁场生物医学应用中所需求的高电压大电流宽范围脉冲问题,文中采用脉冲叠加的方案设计了一种长脉宽固态直线型变压器驱动源(Linear Transformer Driver, LTD)。该LTD脉冲发生器为了突破脉冲变压器伏秒积限制下的脉宽范围,采用并联叠加的方式增加输出脉宽。设计了脉冲变压器的复位电路,提高了LTD输出脉冲占空比,能够实现最少支路LTD的多次脉冲叠加。通过Pspice搭建仿真电路模型进行仿真实验,结果表明在单匝脉冲变压器伏秒积为146 V·ms的情况下,实现单级电压为300 V,脉宽为1.6μs的脉冲输出,为其原伏秒积的3倍,且所提方案能够通过增加叠加脉冲个数来实现更宽范围的脉冲延长。

多级谐振充电的Marx脉冲源研究

Marx发生器是一种经典的脉冲功率发生装置。为了更好地满足高电压、双极性高效率等实际使用需求,文中提出了多级谐振充电的Marx脉冲源,即利用串联谐振充电源与串心磁环变压器对Marx脉冲发生器分组充电。搭建两类对称结构多级谐振充电的Marx脉冲发生器并验证其性能,包括可变极性的单极性发生器和双极性脉冲发生器。电路由一组正极性的3路8级Marx和一组负极性的3路8级Marx组成,共48级。实验结果表明,可变极性的单极性Marx发生器可产生正极性或负极性电压幅值为30 kV的脉冲,双极性发生器可向空载和50 kΩ的阻性负载输出±10 kV的电压脉冲。通过FPGA(Field Program Gate Array)的信号控制可以将重复频率控制在1 Hz~1 kHz范围内调节,脉宽可在1~200μs范围内调节,脉冲前后沿为50 ns以内。正、负脉冲之间的弛豫时间为0.2~200.0μs。

面向绕组监测的磁隔离直线变压器脉冲源研制

针对脉冲频率响应法中对激励信号的波形要求,研制了磁隔离型直线型变压器脉冲信号源,用于产生高压纳秒脉冲信号。该脉冲源采用三级模块结构,并采用MOSFET作为放电主开关,每级模块包含4个MOSFET(两串两并)。MOSFET驱动电路中摒弃了常规光隔离驱动,采用磁隔离方式驱动MOSFET开关,仅采用两个磁芯驱动12个MOSFET开关。输出的高压脉冲信号为:电压幅值最高可达1 500 V,脉冲宽度100~600 ns可调,上升沿及下降沿均小于20 ns,高要求地满足脉冲频率响应法中激励信号的要求。此外,该结构简单,易实现,以磁隔离方式驱动,能够降低研制成本及降低现场环境中的光信号干扰。

脉冲核磁共振基础仿真实验平台设计与实现

为了解决医学影像技术或智能医学影像工程等专业核磁共振实验教学面临的难题,基于数值仿真技术搭建了脉冲核磁共振基础仿真实验平台。该平台可实现核磁共振信号的检测、磁场强度的间接测量、磁场均匀性的测量与调节、射频脉冲角度的确定等功能,平台支持参数任意设置与调节、信号动态采集与显示、频谱快速生成与读取、采样停止与信息提示,该虚拟仿真实验平台操作简单,灵活可控,支持多终端在线操作,为学生学习物理原理和观察物理现象提供了处处能学和时时可学的资源,有助于学生理解抽象的物理原理,增强实验教学的效果。