Power losses in steel pipe delivering very large currents

This paper presents a finite difference time domain solution for the electromagnetic fields in ferromagnetic conducting steel pipes of the type used to deliver large currents for in situ heating of heavy oil reservoirs and for in situ environmental decontamination. A method is described whereby a single measured hysteresis loop can be used to deduce the family of hysteresis loops that governs the variable magnetic behavior throughout the pipe wall. Hysteresis and eddy current losses are calculated, and it is shown that hysteresis effects greatly alter the eddy current distribution and can more than triple the total power losses in the steel pipe when compared to the power losses that would be present if hysteresis effects are ignored and magnetic permeability is assumed constant     

MnZn铁氧体功率损耗特性研究

采用固相反应法制备了Zn0.23Mn0.70Fe2.07O4功率铁氧体材料.研究了材料的静态磁参数和功率损耗;并在100kHz、200mT下对MnZn铁氧体材料的损耗进行了分离.结果表明,试样的Ⅱ峰在80℃左右,与磁滞损耗Ph极小值对应温度一致.材料的损耗特性随温度变化很大,在常温下,磁滞损耗Ph占了材料总损耗的大部分...     

改善电压型PWM整流器DPC系统性能的策略

通过电压型PWM整流器的数学模型,分析了PWM整流器直接功率控制(DPC)的原理,讨论了功率滞环比较器环宽对PWM整流器的影响.为降低开关频率和减少开关损失,需增加功率滞环比较器环宽,否则引起瞬时有功功率和直流电压波动,影响系统的性能;对此,提出了一种设置扇形边界死区的控制策略,即消除在扇形边界误选开关量,使瞬时有功功率和直流电压波形趋于平稳,从而改善了系统的性能.通过Simulink环境下的仿真模型仿真,证明了该策略的可行性.     

DSP控制的低开关损耗PWM整流器系统研究

采用负载电流前馈的电流滞环控制策略,不仅满足了三相PWM整流器高功率因数、直流侧电压稳定可调的控制要求,而且在每个周期内分区限制功率器件的开关通断,因而降低了系统的开关损耗.该系统改进了传统滞环控制策略带来的高开关频率问题,并通过引入负载电流前馈控制,使得系统对于外环的PI参数有着较传统滞环PWM整流器更低的依赖性,在三相电网小平衡的条件下也表现出更好的运行特性.仿真波形和实验数据验证了该控制方法的有效性以及对PI调节参数的低依赖性.     

基于低开关损耗新型滞环PWM整流器研究

针对三相高功率因数整流器的控制要求和实际工程条件,进行了基于低开关损耗的三相PWM整流器研究,系统采用了负载电流前馈的电流滞环控制策略.该系统不仅改进了传统滞环控制策略带来的高开关频率的问题,更引入了负载电流前馈控制,使得系统对于外环的PI参数有着较传统滞环PWM整流器更低的依赖性,在三相电网不平衡的条件下也表现更好的运行特性.仿真波形和实验数据都验证了该控制方法的有效性以及对PI调节参数的低依赖性.     

MnZn功率铁氧体高频功耗特性分析

采用氧化物陶瓷工艺制备了2～4MHz频段高频开关电源用MnZn功率铁氧体,通过对铁氧体断面显微结构、密度和磁特性的测试,研究了Fe2O3含量对MnZn功率铁氧体功率损耗特性的影响。结果表明,随着Fe2O3含量的增加,晶粒尺寸逐渐减小,常温下3MHz、10mT高频损耗(Pcv)先增大后减小,Fe2O3含量从58mol%增加到59 mol%时,损耗下降非常明显,而在100℃时,铁氧体的剩余损耗逐渐降低,导致总损耗随着Fe2O3含量的增加而减小。随着频率的升高,剩余损耗(Pr)占总损耗的比重逐渐增加,成为损耗的主要部分,而磁滞损耗(Ph)占总损耗的比重逐渐降低,涡流损耗(Pe)所占比重变化不明显。     

How to compensate for the reactive and distorting powers in ship electric power systems

Procedures used to compensate for reactive and distorting powers that do not create active power, but rather cause additional power losses and failures in consumer equipment are examined. It is shown that promising procedures for compensating for reactive power can be implemented using similar methods that take into consderation the peculiarities each of them. It is suggested that reactive energy be compensated for based on powerful low-frequency keys with current modulation using a traditional procedure with a stable carrier frequency; the implementation of active filtration based on high-frequency keys with hysteresis control of modulation is also recommended.     

MoO3添加对高频MnZn功率铁氧体性能的影响

采用陶瓷工艺制备高频MnZn功率铁氧体材料,研究了MoO3添加对材料微结构和磁性能的影响。用X射线衍射仪(XRD)、扫描电子显微镜(SEM)表征材料结构,用B-H分析仪测试材料磁性能,并对材料功率损耗进行分离。结果表明,适量添加MoO3可以有效改善材料的微观结构,提高致密度,提高材料饱和磁通密度和起始磁导率,降低功率损耗。功耗分离后发现,随着MoO3添加量的增加,磁滞损耗比例下降,涡流损耗所占比例上升。最佳MoO3添加量为0.01 wt%,获得低功耗的MnZn功率铁氧体,100℃、500kHz、50mT条件下功耗为86 kW/m3,起始磁导率约为1928,25℃下的饱和磁通密度为513 mT。     

Assessment of power losses of an inverter-driven induction machine with its experimental validation

Detailed power loss distribution in induction machines is assessed using time-stepped finite-element analysis coupled to circuit equations of an inverter. Losses are examined for various load conditions. Iron losses are largely unexplored and so particular attention is paid to them here. The simulation has revealed the division between ohmic, hysteresis, classic eddy-current, and anomalous losses; and the distribution in the frequency spectrum between fundamental, slotting, and multiples of the switching frequency. Insight is also gained into the spatial location of the loss. Experimental validation is provided for several fundamental frequencies from full-load to light-load conditions.     

Current Transformer Model

This paper presents a current-transformer (CT) model that is useful for low-frequency applications. To describe the iron-core magnetic behavior, a hysteresis model is proposed, which is able to generate minor asymmetric loops and remanent flux. The effects of classic eddy current losses and anomalous losses are represented by linear and nonlinear resistors, respectively. The obtained results are compared with those calculated by the Preisach's model and measured in the laboratory. This model may be applied in power system protection studies, as it is the case of numeric correction of distorted secondary currents in current transformers (CTs)     

Relation Between Firing Conditions Grain Boundary Structure and Magnetic Properties in Polycrystalline MnZn-Ferrites

The influence of the firing conditions on the nanoscale structure of the grain boundaries and on the magnetic properties of polycrystalline MnZn-ferrites is investigated, on specimens of nearly identical microstructures. High oxygen partial pressures favor accumulation of impurity ions at the triple points. Under appropriate oxygen pressures homogeneous accumulation of impurities along the grain boundaries may occur, revealing therefore chemically pure grains and low hysteresis losses; simultaneously an increase of the grain boundary resistivity occurs that results to low eddy current losses. Managing the raw material impurity cations towards controlled grain boundary structures leads to the synthesis of MnZn-ferrites with power losses similar to those achieved when high purity raw materials are used together with externally introduced additives.     

Computation of Core Losses in Electrical Machines Using Improved Models for Laminated Steel

Two new models for specific power losses in cold-rolled motor lamination steel are described together with procedures for coefficient identification from standard multifrequency Epstein or single sheet tests. The eddy-current and hysteresis loss coefficients of the improved models are dependent on induction (flux density) and/or frequency, and the errors are substantially lower than those of conventional models over a very wide range of sinusoidal excitation, from 20 Hz to 2 kHz and from 0.05 up to 2 T. The model that considers the coefficients to be variable, with the exception of the hysteresis loss power coefficient that has a constant value of 2, is superior in terms of applicability and phenomenological support. Also included are a comparative study of the material models on three samples of typical steel, mathematical formulations for the extension from the frequency to the time domain, and examples of validation from electrical machine studies.     

Analysis of Eddy‐Current Losses in Solid Iron Under dc‐Biased Magnetization Considering Minor Hysteresis Loops

In designing solid‐pole synchronous machines, it is important to take into account the surface eddy‐current losses in the field pole cores. In this study, a solid‐iron ring specimen is adopted as an approximate model of solid‐pole surfaces in order to conduct a fundamental study of the surface losses. The influence of the minor hysteresis loops on the losses under dc‐biased magnetization is investigated. The losses in the ring under dc‐biased magnetization are measured and analyzed by finite element analysis (FEA). The losses computed by the FEA considering minor loops are nearly the same as those measured. In contrast, the eddy‐current losses computed by FEA without considering minor loops are considerably inaccurate because the incremental permeability is overestimated and the skin depth is underestimated. It is important to consider hysteresis for the accurate calculation of the surface eddy‐current losses under dc‐biased magnetization.     

No-load losses in transformer under overexcitation/inrush-current conditions: tests and a new model

Tests were conducted on several transformers rated at 100 kVA or less and on a power transformer rated 370 MVA in an effort to characterize the no-load losses and magnetizing resistance for transformers subjected to overexcitation and inrush current. Analysis of the results revealed that the magnetizing resistance changes as a function of the peak magnetization flux or the amplitude of the magnetic field. A new model of the instantaneous magnetizing resistance (IMR) as a function of the instantaneous flux has been developed and its dynamic use in the Electromagnetic Transients Program (EMTP) allows the form of the hysteresis cycle and the mean losses in overexcitation to be reproduced with a high degree of accuracy. The same model also accounts for losses due to the harmonics superimposed on the fundamental. The results showed that the IMR calculated under inrush current conditions is higher than that in overexcitation conditions.     

三相变流器神经网络滞环控制研究

神经网络技术在人工智能，自动控制以及模式识别等领域的研究与应用正方兴未艾，而滞环电流控制是一种传统常规的电流控制方式，在功率因数和无功补偿等领域有着广泛的应用。该文介绍了三相变流器的BP神经网络滞环电流内环控制，该方案可实现神经网络对快速变量的控制，提高滞环控制的性能，使系统对参数的变化有较强的不灵敏性和鲁棒性。该文分析了三相电源不平衡、某一路电流反馈丢失的工况下，系统的控制特性。为了使系统在轻负载下得到良好的频谱特性，采用实时变误差增益的控制策略，并讨论了容差下限，同时借助于矢量调制的思想，结合神经网络滞环调节器，优化系统性能，减小系统EMI和开关损耗。     

添加Co_2O_3对NiCuZn铁氧体磁性能的影响

采用传统氧化物陶瓷工艺制备NiCuZn铁氧体。利用扫描电子显微镜、阻抗分析仪、磁滞回线分析仪,分别对样品的微观形貌、复数磁导率频谱、静磁性能和高频功耗进行了观察和测试。结果表明,在0~0.12wt%的范围内,随Co2O3添加量的增大,样品的平均晶粒尺寸略有减小,起始磁导率逐渐下降,截止频率逐渐升高。在3MHz、10m T、25~140℃条件下,随着Co2O3添加量的增加,由于截止频率逐渐升高,磁导率虚部在高频下得到抑制,剩余损耗降低,导致磁芯功率损耗单调减小。     

Calculation of losses in ferro- and ferrimagnetic materials basedon the modified Steinmetz equation

This paper discusses the influence of nonsinusoidal flux waveforms on the remagnetization losses in ferro- and ferrimagnetic materials of inductors, transformers, and electrical machines used in power electronic applications. The nonsinusoidal changes of flux originate from driving these devices by nonsinusoidal voltages and currents at different switching frequencies. A detailed examination of a dynamic hysteresis model shows that the physical origin of losses in magnetic material is the average rate of remagnetization rather than the remagnetization frequency. This principle leads to a modification of the most common calculation rule for magnetic core losses, i.e., to the “modified Steinmetz equation” (MSE). In the MSE, the remagnetization frequency is replaced by an equivalent frequency which is calculated from the average remagnetization rate. This approach allows, for the first time, the calculation of the losses in the time domain for arbitrary waveforms of flux while using the available set of parameters of the classical Steinmetz equation. DC premagnetization of the material, having a substantial influence on the losses, can also be included. Extensive measurements verify the MSE presented in this paper     

双降压式全桥逆变器

为避免桥臂功率管直通问题和提高输入直流电压利用率,在全桥逆变器和双降压式半桥逆变器的基础上,提出了双降压式全桥逆变器(dual buck full-bridge inverter,DBFBI),该逆变器具有无桥臂直通、输入直流电压利用率高、效率高、续流二极管可优化选取等优点。半周期调制方式减小了功率管的开关损耗及导通损耗,分析了半周期调制方式下电路的工作模态,给出了电感电流连续与断续时输入输出电压关系。设计了采用滞环电流控制的双降压式全桥逆变器系统,通过控制逻辑设计使之实现了半周期运行模式。仿真和实验结果证明该逆变器具有高质量的输出电压波形和良好的动态响应特性。     

考虑附加涡流损失的超磁致伸缩执行器动态模型

超磁致伸缩执行器在高频下工作时,能量损失不仅包括磁滞损失、Terfenol-D棒涡流损失,还包括Terfenol-D棒附加涡流损失。该文考虑到执行器的惯性、阻尼、Terfenol-D棒涡流损失及附加涡流损失,建立了超磁致伸缩执行器的动态模型。其磁滞特性由Berqvist和Engdahl磁滞模型来描述,材料非线性由输入到模型静态实验数据体现。模型求解使用有限差分方法,在Matlab/Simulink中建立相应模型仿真结构框图。对执行器不同工作频率情况进行模型的仿真计算,并与实验结果对比,发现模型与实验吻合较好。表明所建立动态模型能较好地描述执行器输出位移与驱动电流之间的关系。该模型对优化设计超磁致伸缩执行器有指导意义。     

用数字仿真计算畸变电压条件下电力变压器的正弦磁滞损耗

详细阐述了计算畸变电压条件下变压器低损耗硅钢片铁心中磁滞损耗的一种数字仿真方法。这种方法使用的模型是以分段线性化去模拟铁心材料的稳态Ｂ／Ｈ特性曲线为基础的。根据模拟的Ｂ／Ｈ特性曲线求出主磁滞回线和小磁滞回线的面积，从而计算出空载损耗实测值中的磁滞损耗和涡流损耗分量。最后计算出电源电压为正弦形时的变压器空载损耗。计算值和试验结果吻合很好。这种方法可以用于电源电压畸变时校正测出的变压器空载损耗。