A new approach to calculating core losses in the SRM

In switched reluctance motors (SRM), the flux waveforms are nonsinusoidal and different parts of the magnetic circuit have different waveforms. This paper presents a new approach of taking account of these flux waveforms in the calculation of core losses. Relations between the fluxes of different parts of the magnetic circuits are given in the form of matrix equations, where the fluxes are expressed in terms of normalized flux pulses. Rewriting the eddy-current loss term in the Steinmetz equation in terms of the square of dB/dt and combining it with the matrix equations, eddy-current losses for the complicated flux waveforms of the stator and rotor yokes are calculated. The effect of PWM is taken into account by considering the PWM voltage waveform as dB/dt. From the matrices, it is easy to count how many times full and minor hysteresis loops occur at each pole and yoke segment. The effect of the minor loop is taken into account based on experimental results. The proposed approach gives a systematic procedure for core loss calculation. The derived equations are simple and useful in the design of SRM     

开关磁阻电机铁损的双频法有限元计算研究

文中对1台三相12/8结构开关磁阻电机进行了四分之一域的二维(2D)电磁场有限元分析,得到了大小和方向都随时间变化的铁心磁密矢量的X和Y分量,从而更细致地描述了电机铁心各单元磁密随时间(转子位置角度)的变化周期和规律。在无需知道电机铁心材料的损耗系数(即涡流修正因子和局部磁滞回线因子)的情况下,以磁密的计算信息和铁心材料单位体积的铁损密度数据为基础,通过双频法分离出铁损中的涡流损耗和磁滞损耗,再用频率分解法和最大磁密法分别计算这2种损耗,并对占电机铁心铁损较大比例的涡流损耗进行了离散傅里叶分解,比较各次谐波分量对铁损的影响。由间接法计算出铁损的实验值,近似地分离了铁损和杂散损耗,实验验证了该铁损计算方法的准确性。     

A study of the loss characteristics of the amorphous magnetic material under nonsinusoidal wave magnetic flux

This paper presents a study on iron loss characteristics of an amorphous magnetic material under nonsinusoidal wave magnetic flux. The iron loss characteristics of the amorphous magnetic material have been compared to those of grain‐oriented magnetic steel sheets. Measurements of the iron loss have been carried out by means of an SST. It was found that the ratio of the iron loss increase of the amorphous magnetic material under the excitation by distorted waveforms and symmetric PWM waveforms is lower than that of grain‐oriented magnetic steel sheets. On the other hand, the ratio of the iron loss increase of the amorphous magnetic material under the excitation by asymmetric PWM waveforms is higher than that of grain‐oriented magnetic steel sheets. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 11–18, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20004     

非正弦励磁下磁芯损耗的计算

磁性元件的损耗在开关电源中占相当大的比例,因此磁芯损耗的计算在开关电源设计中相当重要. 文中首先介绍了在正弦励磁下,计算磁芯损耗的Steinmetz 经验公式,然后对修正的Steinmetz 经验公式进行了回顾.修正后的公式可以用来计算非正弦励磁下的磁芯损耗,同时所需参数和修正前的公式一样.最后介绍修正的Steinmetz 经验公式在开关电源领域中的应用.     

Modeling of losses in switched reluctance machines

Switched reluctance motor (SRM) performance prediction requires the modeling of iron losses. The iron loss model in this paper separates the iron losses into two components, eddy-current and hysteresis losses, and models the losses as a function of the derivative of flux density. The model is suitable for the nonsinusoidal flux densities in the SRM and predicts the iron losses as a function of time. The model is general and can be applied to any electromagnetic device with known geometry and material property. The equations of iron loss are verified and validated through experiments with two simple geometries (a transformer and a toroid) and two SRMs.     

考虑旋转磁通的PMSM铁心损耗数值计算

为了准确计算交流永磁同步电机(PMSM)铁心损耗,采用二维有限元法对PMSM定子与磁极区域电磁场进行了分析研究,阐述了定子铁心不同区域磁场的变化规律及磁极区域涡流场的分布规律.在此基础上,借助谐波分析的方法,综合考虑电机中交变与旋转磁场的影响,给出了一种较准确求解定子铁心损耗和PMSM转子涡流损耗的计算方法,并与传统的计算方法进行了比较.结果表明,考虑旋转磁场及谐波磁通密度影响时的定子铁心损耗计算值与传统的仅考虑交变基波磁通密度时的损耗计算值相比有显著增加,更接近于实际测量值,磁极涡流损耗值与定子槽口大小密切相关,占电机总损耗的比重较大,是不可忽略的.     

Core losses in motor laminations exposed to high-frequency or nonsinusoidal excitation

This paper first reviews three internationally standardized core loss measurement methods: the Epstein frame, toroids, and single sheet testers. A comparison of the Epstein frame and toroid test results is presented for annealed and unannealed steel. Two methods are used to predict core losses under nonsinusoidal supplies. The first method uses the Fourier series and an improved loss separation algorithm to predict no-load core losses under brushless DC motor flux waveform excitation with a flux density known spectrum. The second method uses the form factor concept and an improved loss separation algorithm to predict core loss. The combination of the improved loss separation algorithm and the form factor concept was found to yield results close to the measured losses under high-frequency supplies, such as pulsewidth-modulated waveforms. An Epstein frame with commercial 0.0140-in (0.356 mm) electrical steel was used for direct core loss measurements; the methods and test bench used are detailed in the paper, along with test results.     

方波激励下纳米晶体铁心损耗模型建立与验证

为了实现电力机车小型化轻量化的发展要求,国内外专家考虑通过采用提高变压器的工作频率减小变压器整体的体积和质量。铁心作为高频变压器的关键部件,可以准确计算铁心损耗,对中高频变压器的设计和优化具有重要作用。针对高频变压器铁心通常是工作在方波或脉宽调制(PWM)波等非正弦激励下的特点,对传统Steinmetz损耗计算模型进行了优化改进,给出了考虑磁密的变化率及波形系数对损耗的影响的Steinmetz改进损耗模型。同时,为了提高损耗模型在不同特征频率下的通用性,进一步对损耗模型系数的非线性进行研究,给出了模型系数随频率变化的非线性函数。最后,利用有限元计算结果同实物测量结果进行比较,证明了所提损耗模型在方波激励下对纳米晶体铁心计算的准确性。     

About the possibility of defining a standard method for iron lossmeasurement in soft magnetic materials with inverter supply

Due to the increase of electromagnetic and electromechanical devices supplied by static converters, the classification and evaluation of the energetic behavior of soft magnetic materials, with nonsinusoidal supply, is becoming mandatory. In this paper, the possibility of defining a standard methodology for the specific iron loss measurement (iron losses per mass unity), with static supply, is analyzed. In particular, the paper underlines the main problems which can be found when standard magnetic measurements are carried out with nonsinusoidal sources. Pulsewidth modulation (PWM) inverters can be considered an industrial standard solution as a static supply source. As a consequence, the problems linked to the use of this kind of supply with magnetic material have been analyzed, taking into account the effects due to the PWM inverter characteristics (for example, modulation index, switching frequency, and modulation technique). In addition, in the paper, a basic structure of a standard test bench is proposed, also taking into consideration the required instrumentation     

可变磁通永磁记忆电机调磁特性

建立了可变磁通永磁记忆电机永磁体连续去磁和重新充磁的磁化模型,给出了去磁时的回复线方程和充磁时的局部磁滞回线方程,采用有限元法对电机施加不同定子直轴电流时的磁通分布和永磁体内的磁通密度变化进行了分析,据此计算了电机永磁体在不同磁化状态时的气隙磁通密度、相磁链、相反电动势、每极气隙磁通等参数。文中给出了记忆电机连续去磁与充磁的有限元分析流程。设计制作了一台样机进行了实验验证,实验结果与有限元计算结果吻合较好。有限元计算与实验结果同时表明,记忆电机能实现连续近似线性去磁,但增磁特性呈非线性;永磁体的充磁比去磁困难,饱和充磁电流大约是完全去磁电流的4倍。     

开关磁阻电机的磁通波形

本文阐述了开关磁阻电机(SR电机)在不同工作状态下的磁通波形的形状及变化规律,提出了磁通波形矩阵形式的数学模型,有效地解决了任意相数SR电机铁芯不同部分的磁通波形的合成问题,并首次应用非线性方法计算分析了不同转速和控制策略下铁芯各部分的磁通波形。本文的研究结果为SR电机的铁耗分析和计算提供了基础。     

PWM逆变器供电引起的轴向磁通非晶电机谐波损耗的解析计算

非晶合金材料具有出色的低损耗特性,适于用作高频电机的铁心,但PWM逆变器供电会导致高频电机谐波损耗严重增加。在电机初始设计阶段,快速准确计算出谐波损耗是轴向磁通非晶合金永磁电机设计及优化的关键。针对3D时步有限元计算耗时长的问题,改进现有多环等效模型的计算方法,推导了考虑PWM逆变器供电高次谐波电流影响的气隙磁通密度解析计算方法,并在此基础上推导了定子铁心损耗及考虑涡流反作用影响的转子涡流损耗的解析计算方法。将谐波损耗的解析计算值与样机实验值以及3D有限元计算值进行对比,结果显示谐波损耗的平均计算误差仅为9.69%,解析模型具有较高的计算精度。     

基于损耗分析的大容量高频变压器铁芯材料选型方法

铁芯材料的选择对大容量高频变压器的磁拓扑性能具有决定性影响,而损耗特性最为关键。为此,针对高频方波激励,采用改进的Steinmetz公式分析了变压器3种常用磁性材料即铁氧体、纳米晶和非晶材料的损耗特性与频率、磁通密度的关系,并给出了磁性材料损耗密度的三维表征图。在对损耗密度进行分析的基础上,将铁芯总损耗与高频变压器视在功率的比值定义为损耗因子,并依据损耗因子的三维表征图与实例分析,结合工作频率和体积等因素比较了3种典型磁性材料所制成的铁芯的损耗特性。分析指出,损耗因子是衡量高频变压器损耗特性优劣的重要指标,以最低损耗因子水平结合体积与成本因素进行分析,可作为铁芯材料的具体选择准则。     

基于谐波分析法的高速变频电机铁耗计算方法

提出了一种计算非正弦供电时的高速变频电机铁耗的简单而有效的方法。该方法以谐波分析法为基础，能够综合考虑电源谐波、电机铁芯饱和以及集肤效应的影响，具有较高的精度。与有限元法计算结果的比较表明，该方法具有较高的精度。     

A 2D approximation of standard electrical steel losses and permeability

A first design approach for an electrical machine need not be done with the efforts of detailed magnetic field considerations. Often a more pragmatic way already fulfills the desired accuracy. Performing fast by hand calculations depends on the data that is available; for e.g., the lamination geometry or material. This article provides a table for different electrical steels that can be used in the analytical calculation of magnetic circuits. In comparison with existing publications this article shows two-dimensional functions for the specific iron losses and the relative permeability. Both magnetic flux density and frequency are input variables.     

双向全桥DC-DC变换器中大容量高频变压器绕组与磁心损耗计算

精确预估非正弦波激励下高频变压器绕组与磁心损耗、研究不同模态下变压器损耗的变化趋势,对于电力电子变压器(PET)精细化设计至关重要。在对PET中间级——隔离式双向全桥DC-DC变换器工作原理进行分析的基础上,建立变换器的近似等效电路模型,得到一种适用于隔离式双向全桥DC-DC变换器中高频变压器绕组损耗计算方法。在计算方波、梯形波电压激励下的磁心损耗时,推导出修正的Steinmetz经验公式简化解析计算式,引入仅与占空比和上升时间有关的修正系数,据此可直接利用正弦波激励下的损耗系数,快速获取典型工作模态下磁心损耗。设计制作一台1.2k V/0.3k V/5k V·A非晶合金磁心高频变压器试验模型,将所提方法的计算结果与有限元仿真和试验测量结果对比,验证了所提方法的有效性。     

非正弦激励时变频电机铁耗计算方法研究

针对变频电机铁耗分析中存在的铁磁材料建模,非正弦激励时铁耗计算模型等问题,结合近年来为解决这些问题所提出的理论和方法进行了系统地综述和分析,指出了现有各种方法的优缺点,并提出了今后变频电机铁耗分析的研究方向.     

异步电机铁心损耗计算方法的分析与研究

采用变频启动、自启动、串电阻启动等方式启动的异步电机内的组成部件中的电磁场分布并不相同,因此各组成部件的损耗分析方法也应各不相同.各种形式的斯坦梅茨方程可分析计算铁心损耗,且斯坦梅茨方程中的系数可由硅钢片制造商提供的损耗曲线获得,然而,硅钢片制造商提供的损耗曲线仅能在几个固定的频率下获得.采用了一种曲线拟合技术,可计算...     

电力系统动态频率测量的"虚拟电枢磁势"法

提出利用三相电压采样值计算频率的“虚拟电枢磁势”法,此方法构想了一种“虚拟电机”,以它的“电枢磁势”的旋转角速度作为节点的动态频率。此方法在计算过程中,能够滤除零序分量,在结合自适应调整采样周期方法之后,又消除了整次谐波和负序分量对测量频率的影响,跨越了繁琐复杂的滤波和滤序的过程,快速精确地测算了真实的电力系统实时频率。     

Performance and torque-ripple characterization in induction motoradjustable-speed drives using time-stepping coupled finite-elementstate-space techniques

In this paper, the time-stepping coupled finite-element state-space (TSCFE-SS) model developed in an earlier companion paper is applied here for assessments of effects of machine geometry and magnetic circuit design modifications, and effects of pulsewidth modulation (PWM) carrier frequency on performance characteristics of induction motor drives. Namely, this has been accomplished through analysis of developed torque profile ripples and harmonic spectra of mid-air-gap radial flux density waveforms of the case-study motor. Furthermore, consequent effects of design modifications pertaining to geometry and/or magnetic circuit modifications and PWM carrier frequency on ohmic and iron core losses are investigated. The investigation has been performed on a case-study motor, which is a Y-connected single-layer three-phase two-pole 1.2-hp 208-V squirrel-cage induction motor with 24 stator slots and a cage with 34 rotor bars