Magnetic core model for circuit simulations including losses and hysteresis

This paper presents a magnetic core model that accounts the effects due to nonlinearity, hysteresis and eddy currents. The model is suited to circuit simulation and can be implemented as a subcircuit. To test the proposed implementation the results obtained by simulating a power square wave generator (Royer oscillator) have been compared with measurements on a laboratory prototype. Copyright © 2008 John Wiley & Sons, Ltd.     

A systematic method for the development of a three‐phase transformer non‐linear model

In this work, a novel three‐phase transformer non‐linear model is developed. The proposed model takes into account the magnetic core topology and the windings connections. The non‐linear characteristic curve of the core material is introduced by its magnetization curve or by its hysteresis loop using the mathematical hysteresis model proposed by Tellinen or the macroscopic hysteresis model proposed by Jiles–Atherton. The eddy currents effects are included through non‐linear resistors using Bertotti's work. The proposed model presents several advantages. An incremental linear circuit, having the same topology with the magnetic circuit of the core, is used in order to directly write the differential equations of the magnetic part of the transformer. The matrix L _d that describes the coupling between the windings of the transformer is systematically derived. The electrical equations of the transformer can be easily written for any possible connection of the primary and secondary windings using the unconnected windings equations and transformation matrices. The proposed methods for the calculation of the coupling between the windings, the representation of the eddy currents and the inclusion of the core material characteristic curve can be used to develop a transformer model appropriate for the EMTP/ATP‐type programs. Copyright © 2009 John Wiley & Sons, Ltd.     

Eddy currents generated in a system of two cylindrical conductors by a transverse alternating magnetic field

In the paper, using the Bubnov–Galerkin method coupled with the separation of variables method, the eddy currents in a system of two cylindrical conductors placed in a transverse homogeneous magnetic field sinusoidally varying with time are investigated. The power losses caused by these currents are also determined. By dint of computer calculations, the graphs of these losses are traced.     

An induction machine model including interbar currents for studying performances during transients and steady state

This paper presents a mathematical model of a three-phase induction motor taking into consideration the interbar contacts. Several models have been available in the references. However, they consider the rotor of the induction motor as being constituted either a three-phase or a squirrel cage even if it operates under stator and/or rotor faults condition. Nonetheless, the contact between a bar and the iron core for the machine has to be considered, especially when a rotor fault occurs. It is obvious that rotor currents are under the influence of rotor constitution materials. So, the paper aim’s concerns a transient model of the induction motors which can consider the rotor broken bars defect. Despite its increasing complexity, it could be able to provide with useful indications for diagnostic purposes. This model is advocated for the simulation of motors behavior under rotor defect which takes into account the interbar currents. The proposed technique is based on the mesh model analysis of the squirrel cage. As low power induction motors are prevalent in industrial plants, we pay a special attention on them. Notwithstanding, additional currents are due to the contact between the non-insulated bar constituting the squirrel cage to the rotor iron core. The monitoring of induction motors is predominantly made through the stator current analysis of the motor when it operates at nominal condition. Moreover, this one is observed in steady state operating system, knowing that the motor is generally fed by a sinusoidal supply. Consequently, simulation results showed in this paper prove the effectiveness of the proposed approach, and the impact of interbar resistance both on the model and the line current spectrum for the diagnostic. An experimental test proves the effectiveness of this model.     

基于人工神经网络的Preisach磁滞模型与实现

在Preisach静态磁滞模型的基础上,利用极限磁滞回线的对称性,采用人工神经网络技术,建立了Preisach神经网络磁滞回线仿真模型,实现了对试验样片交流磁滞回线的理论计算;同时给出了一种采用爱泼斯坦方圈,对实验样片的动态磁滞回线进行数字测量的新方法,该方法实验设备简单,测量精度高,具有较好的工程实用价值。利用该方法得到的实验数据很好地验证了理论计算结果。     

基于Preisach磁滞模型的分布函数辨识与实验验证

基于Preisach磁滞模型,根据磁滞回线的对称性,提出辨识Preisach分布函数的方法,该方法把Preisach分布函数视为两个一维函数的乘积,将分布函数中复杂的双重积分求解问题转化为求解双线性方程组的问题。并基于爱泼斯坦方圈测量装置对变压器、电机中常用材料(B30P105)进行了相应的实验,仿真及实验结果的比对验证了该方法的可行性和实用性。     

电力变压器磁屏蔽模型损耗三维有限元分析及实验研究

针对大型电力变压器铁磁结构件中(例如油箱)产生的电磁损耗导致局部过热,使相关的绝缘部件受损,进而危及整个变压器的正常运行现象,笔者提出以国际TEAM Problem 21基准磁屏蔽(简称为板式和立式屏蔽)模型为例,采用分离激励线圈电阻损耗和涡流损耗的测量方法(漏磁通补偿线圈测量装置),对变压器取向硅钢叠片中的磁通和损耗进行计算和试验测量。其计算与测量结果表明,该方法较好地解决了线圈损耗和结构件损耗分离的问题。同时,也验证了三维非线性涡流场分析和损耗模拟方法的有效性。     

可直接分析与计算的变压器等效电路模型

针对电网中不同电压等级网络间分析和计算方法复杂,不能进行直接分析与计算的问题,依据电路的网络理论,提出了一种含理想运算放大器的变压器等效电路,采用理想运算放大器实现受控源的方式,建立了变压器工程化模型电路,并对电路的网络方程进行了理论推导和电路的模型进行了仿真.仿真结果表明,该工程化模型不但能模拟等效变压器电路,而且电路方程也满足变压器的网络方程,从而在含有变压器的电网中实现了不同电压等级网络间的直接仿真分析与模拟计算.     

Current and voltage excitations for the eddy current model

We present a systematic study of how to take into account external excitation in the eddy current model. Emphasis is put on mathematically sound variational formulations and on lumped parameter excitation through prescribed currents and voltages. We distinguish between local excitation at known contacts, known generator current distributions and non‐local variants that rely on topological concepts. The latter case entails the violation of Faraday's law at so‐called cuts and prevents us from reconstructing a meaningful electric field. Copyright © 2004 John Wiley & Sons, Ltd.     

变压器有载合闸的非线性数学模型及仿真

已提出的变压器有载合闸模型,都是将时变的励磁电感进行线性化或分段线性化处理,这种处理方式不能光滑地反映铁芯的非线性特征,造成仿真误差。建立了一个比较合理且精确的变压器有载合闸的非线性数学模型,铁芯的励磁特性采用了多值磁滞特性。根据该模型建立各支路电流的状态方程,并通过数字实时仿真证明了目前各种采用涌流特征进行闭锁的变压器差动保护经历带负载合闸时,尤其是在外部故障切除后电压恢复过程中受超饱和现象的影响,存在误动的可能性,指出应规定不推荐进行变压器有载合闸。进一步验证了变压器差动保护原理的局限性。     

基于谐振电抗器和磁能恢复开关的单相AC-DC变换器

将谐振电抗器和磁能恢复开关引入到单相AC-DC变换器中,设计了一种新颖的混合单相AC-DC变换器.在理论分析谐振电抗器和磁能恢复开关单独在单相功率因数校正器(PFC)应用中的优点和不足的基础上,提出了一种结合两者长处的功率因数校正方法,能够获得更高输入功率因数(PF)和更高输出直流电压.并利用仿真软件ORCAD 10.5建立了完整的单相AC-DC变换器-逆变器仿真电路,对上述3种情况进行了FFT和参数扫描等仿真分析.结果说明了所提出的方案是可行的和低成本的,能够支持较大的输出功率,可以作为变频家用电器等的前级单相AC-DC变换器.     

基于耦合漏感的四绕组变压器暂态模型及短路计算

为确保含四绕组变压器的变电站保护整定可靠性,需研究精细化的四绕组变压器暂态模型及其短路计算等值电路。分析常规变压器等值电路的不足,推导了修正的耦合漏感等值电路,根据三相三柱式四绕组变压器的拓扑结构,运用对偶性原理建立了基于耦合漏感的四绕组变压器电路-磁路暂态模型;利用漏磁路的互阻抗远小于漏阻抗的特点,推导了用于短路计算的四绕组变压器简化等值电路以及零序阻抗。根据某地220 k V变电站实例进行仿真计算,结果表明所提出的四绕组变压器暂态模型及短路计算方法能够更准确地计算含四绕组变压器变电站的短路电流。     

畸变磁通作用下变压器铁心模型损耗的实验研究与模拟分析

对畸变磁通条件下产品级变压器铁心模型的损耗进行了实验研究,考察了谐波相位差变化对铁心损耗的影响。给出了一种能够考虑畸变磁通条件下铁心损耗的工程计算方法,该方法可有效地考虑局部磁滞回环对铁心损耗的影响。结合MagNet电磁分析软件,计算了产品级变压器铁心模型的铁心损耗,通过对比实验结果证明了方法的有效性。     

Circular scanning and equivalent magnetic currents for main plane near‐field to far‐field transformation

A method to obtain a main plane far‐field radiation pattern of an antenna under test (AUT) from the correspondent main plane near‐field pattern in a circular scanning is presented. The method is based on the reconstruction of a set of magnetic equivalent currents radiating in free space that represents the AUT. The method can be applied to the measurement of antennas with a linear distribution or with a two‐dimensional distribution under certain considerations that allow to establish integral equations relating field components and one‐dimensional current components. A Levenberg–Marquardt algorithm is used to minimize the least squares error between the fields radiated by the equivalent currents and the measured field. The far field at every aspect angle is obtained from the calculated sources. Calculations of co‐polar and cross‐polar far‐field pattern from measured near‐field data of array antennas have been carried out to compare the proposed method with a full spherical scanning followed by a spherical wave expansion method. Copyright © 2002 John Wiley & Sons, Ltd.     

Three-dimensional magnetic field analysis of a system containing coil currents and iron elements using the virtual current method

This paper proposes a method of analyzing the three-dimensional magnetic field of a system containing coil currents and magnetic substances using virtual currents. Various methods have been presented for analysis of a three-dimensional static field in an open boundary space; however, in a large-scale problem, the computational size easily exceeds the acceptable limit of computing time and machine capacity. The basic idea of the proposed method is to divide the whole region into interior and exterior regions with an artificial boundary and to substitute virtual currents for source currents and magnetic substances within the boundary. The use of virtual currents reduces the number of elements to be analyzed and shortens computing time while maintaining accuracy of analysis. In this paper, a method of determining virtual current is proposed and principal parameters of virtual currents that affect accuracy of analysis are examined. The conditions under which the virtual current method can be applied are examined through analysis of errors introduced by the virtual current method. This method has been applied to analyze magnetic shielding of a magnet for magnetic resonance imaging. This example proves that the proposed method is effective in reducing the scale of analysis and computing time.     

一种新的变压器磁路到电路的转换模型及多种方法的统一

变压器的建模计算方法有两个关键点,一个是磁化曲线的表示,一个是磁路到电路的等值转换模型。针对第二个关键点提出了一种新的转换模型,把铁芯柱、铁轭、漏磁路径都等效成匝数为一次绕组的线圈,利用电流拆解方法表示各线圈的电流关系,利用磁通的连续性表示电动势的关系,从而得到与磁路等值的电路模型。该电路模型与对偶原理法得到的电路模型相同,并且该模型可以得到与统一磁路UMEC法相同的变压器铁芯动态自感和互感值,验证了所提新方法的正确性以及所提方法、对偶原理法、统一磁路UMEC三种方法的统一。最后给出计及变压器饱和特性的电磁仿真计算流程图。