Parameters affecting bending losses in graded-index polymer opticalfibers

Radiation losses that occur when bending graded-index polymer optical fibers (POFs) are analyzed as a function of the profile exponent, the light wavelength, the fiber core radius, and the length of the bent section. For this purpose, a ray-tracing model is used, which combines both the generalized Fresnel power transmission coefficients for curved graded-index media and the differential equations that govern the ray paths in highly multimode graded-index fibers. This model is applied to the most recent types of graded-index POF, for which the choice of the core radius and profile exponent is discussed from the point of view of bending losses (the greater the profile exponent and the core radius, the greater the bending losses). The influence of profile exponents different from two is included for the first time     

空压机用高速永磁电机铁心和磁钢损耗的影响因素

高速电机具有电流频率高、定子铁耗和转子涡流损耗大等特点。针对额定功率10 kW、额定转速100 000 r/min空压机用高速永磁电机,对比分析了平行充磁和径向充磁、脉冲振幅调制(PAM)方波驱动和基于SiC的正弦波驱动时对损耗的影响。分析结果表明,平行充磁气隙磁密谐波小,空载定子铁心损耗比径向充磁低约40%;驱动方式对电机损耗尤其是转子损耗影响较大,正弦波驱动时转子损耗几乎可忽略,方波驱动时转子损耗占比可达总损耗的20%。针对方波驱动转子损耗大的问题,在转子表面增加一层铜屏蔽层,分析结果表明可以有效降低转子涡流损耗。对同一台带压缩机负载的高速电机对比测试了2种驱动器控制下的母线输入的有功功率,验证了驱动方式对电机损耗的影响。     

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...     

FeCuNbSiB纳米晶合金软磁性能的热处理工艺调控研究

为满足大容量高频变压器对大尺寸纳米晶铁芯低损耗需求,探索了50 mm高纳米晶铁芯的热处理工艺,研究了2种典型纳米晶合金Fe_73.5Cu₁Nb₃Si_15.5B₇和Fe_73.5Cu₁Nb₃Si_13.5B₉（简称B₇和B₉）的热处理温度（330~600℃）对铁芯静态和动态磁性能的影响规律。结果表明：B₇和B₉合金在420℃退火已开始纳米晶化,要远早于通常认为的500℃。2种合金分别在550、580℃退火具有最低的铁芯损耗;而分别在500、550℃退火具有最优的静态磁性能,即最高的磁导率和最低的矫顽力。经施加横向磁场退火后,B₇合金的损耗进一步降低,$P_{\rm{cm}} $（0.5T/20k）达到7.3W/kg,为目前报道的最低铁芯损耗。根据系列数据建立了铁芯损耗分形公式为$ {\mathit{P}}_{\rm{cm}}=0.5{\mathit{f}}^{1.42}{{\mathit{B}}_{{\rm{m}}}}^{2.27} $,预测的准确性得到了实验结果的验证。     

改变定子铁芯面积对分数槽集中绕组永磁同步电机铁耗的影响

为研究改变定子铁芯面积对分数槽集中绕组永磁同步电机中铁耗的影响,针对定子槽提出了两组研究方案.在8极9槽永磁电机的基础上使用有限元软件,搭建了保证定子槽数不变仅增加定子槽宽整数倍和不改变每个定子槽尺寸仅增加定子槽数的两组电机.介绍了铁耗计算原理并通过仿真对比了两组电机谐波含量、定子轭部磁通密度和在不同转速下的铁耗与永磁...     

风电变流器改进型断续脉宽调制策略

大功率风力发电变流器中,存在开关损耗和电流总谐波失真THD(total harmonic distortion)难以均衡的矛盾。如何优化调制方式,以提高系统效率,减小电流谐波,是大功率风电变流系统的核心技术之一。针对风电变流器宽频率、宽电压运行范围的特点,分析直驱风电变流器采用断续脉宽调制策略下的损耗和谐波性能,发现不同工况下主要关注指标不同,轻载时电能质量恶劣、开关损耗低,而重载时开关损耗严重、电能质量好;但是常用调制方式很难兼顾。为解决该问题,提出一种适用于永磁同步机直驱风电变流器的新型断续脉宽调制策略,该调制策略对开关损耗和THD的优化特性随变流器工作范围变化,实现不同工况下主要关注指标的优化。最后通过实验平台验证了该方案在重载时减小开关损耗,在轻载时降低电流谐波的有效性。     

轴向磁场电机永磁体空载涡流损耗减小方法对比研究

减少轴向磁场电机永磁体空载涡流损耗的方法主要有：减小定子槽开口宽度、增大气隙长度、永磁体分块、使用屏蔽层和磁性槽楔等。基于轴向磁场电机的简化二维分析模型,分析了减小定子槽开口宽度和增大气隙长度、使用屏蔽层和磁性槽楔降低空载涡流损耗的效果。通过三维电磁场仿真,研究了永磁体不同分块方式对减少空载涡流损耗的效果。研究结果表明,减小定子槽开口宽度的效果最佳;虽然增加气隙长度可以显著减小涡流损耗,但永磁体用量迅速增加;永磁体分块减小涡流效果较好,且周向分块方式最好;屏蔽层起反作用;使用分段磁性槽楔效果比减小定子槽开口宽度稍微差一点,但加工难度要低些。     

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。     

Millimeter waveband semisymmetrical groove guide resonators

As an alternative to the classical waveguides, such as the H-waveguide and the rectangular waveguide, the groove waveguide has been used at millimetre wavelengths for the last couple of decades. Most of these properties are attributed to the open sides of the guide, which reduce the wall losses. This article describes a semisymmetrical groove guide resonator that is designed and analyzed analytically, numerically, and experimentally. The numerical simulations are performed via a powerful time-domain simulator based on the finite-difference, time-domain (FDTD) method. Both Cartesian- and cylindrical-coordinate FDTD packages are developed and used for the simulations. The purpose in using cylindrical-coordinate FDTD is to calibrate Cartesian-coordinate FDTD and to see the error introduced due to discretization. A measurement setup with an adjustable support platform in the frequency range of 20-40 GHz is used in the experiments.     

Critical Radius of Axial Magnetic-Field Contacts in Vacuum Interrupters

Vacuum circuit breakers (VCBs) are widely used to protect medium-voltage (MV) power distribution circuits. Since SF$_{6}$ gas is specified as a global warming gas, VCBs are stepping into a higher voltage sector to protect power transmission circuits. Axial magnetic field (AMF) contacts are widely used in vacuum interrupters. In this paper, we propose a concept of critical radius of AMF contacts. When coil width and coil height are fixed, the axial magnetic flux density increases first with increasing contact diameter. Then, it reaches a maximum value. Thereafter, the axial magnetic flux density decreases. The contact radius corresponding to the maximum axial magnetic flux density is critical radius. The concept of critical radius is validated by coil-type AMF contacts and slot-type AMF contacts in MV vacuum interrupters with finite-element analysis. Critical radius is only related to contact geometry parameters and the current has no influence on critical radius. Critical radius increases with increasing contact gap, coil width, coil height, and thickness of the contact plate. In high-voltage AMF vacuum interrupters, axial magnetic flux density per kiloampere increases with increasing contact diameter since the critical radius is typically high with a high contact gap and it is in the rising branch. In an MV AMF vacuum interrupter, interrupting capacity could increase with an increase of the contact diameter with a different rising rate before and after the critical radius. This is expected to be experimentally validated.      

考虑谐波及集肤效应的电工钢片旋转异常损耗计算与测量

为了准确计算电工钢片的旋转异常损耗,根据谐波分析原理对建立的电工钢叠片有限元模型进行时步有限元仿真;基于旋转铁心损耗计算模型,通过考虑涡流集肤效应对旋转损耗系数的影响结合钢片在中低频率下的损耗测试获得叠片损耗计算的关键系数,间接求得电工钢片中旋转异常损耗的计算式。利用构建的新型三维磁特性测试系统对典型电工钢叠片样品进行椭圆形旋转与交变励磁方式下的宽频铁耗实验测量,并定量地进行了对比与分析。结果表明:2种励磁方式下叠片损耗的变化规律相类似,但其椭圆形旋转各损耗都要比交变时的对应损耗大,必须认真考虑谐波、集肤效应和旋转励磁等对材料特性的影响;所计算出的旋转异常损耗也是相对较小,在1 k Hz时也未占到旋转总铁耗的5%。从而验证了所推导出的计算式和测量手段的正确性与可行性。     

Simulations on an SOI grating-based optical add/drop multiplexer

With a suitable design of a silicon-on-insulator (SOI) grating in an optical add/drop multiplexer (OADM), a wavelength-selectable OADM is described. We study the characteristics of the designed SOI OADM and simulate the relationship of the electron and hole concentrations including the temperature effect by using integrated system engineering-technology computer aided design. The voltages for the light wavelength switching are evaluated and are best set below V/sub p/=0.8 V and above V/sub n/=-0.8 V for OADM operation. The light propagation and spectral response are also illustrated in finite-difference time-domain beam propagation method (FDTD-BPM) simulations.     

DCM模式逆变器的定环宽电压滞环控制

针对单相半桥逆变器,文中提出了一种定环宽的电压滞环零电流开通控制方式。传统的逆变器工作于连续导通模式(Continuous Conduction Mode,CCM),使得开关损耗大降,低了逆变器的工作效率,而硬件上增加谐振电路实现软开关的方式,虽能减小开关管的损耗,却依旧无法提高逆变器的整体使用效率,为此,文中提出了一种定环宽的电压滞环控制方式,该方式通过使逆变器工作于不连续导通模式(Discontinuous Conduction Mode,DCM),不仅可以大幅减小滤波电感的体积,更能减小开关管的开通损耗提高逆变器的工作效率。文章还研究了定环宽下滞环宽度对谐波畸变率的影响,基于仿真结果进行线性分析,得出其量化函数关系。     

分数槽集中绕组表贴式永磁同步电机转子损耗

针对损耗模型很难准确地计算转子损耗且三维有限元方法占用大量时间的问题,基于二维运动瞬态有限元法,研究了1台36槽42极单层分数槽集中绕组永磁同步电机在恒转矩区和弱磁区以最大转矩运行时的转子损耗,并且研究了高速工况下永磁体轴向分段数量、槽口宽度以及气隙厚度对永磁体损耗的影响。研究发现,在整个转速区间永磁体损耗占转子总损耗的90%以上;转速低于1 500 r/min时,转子铁心磁滞损耗高于涡流损耗,高于1 500 r/min时涡流损耗明显高于磁滞损耗。永磁体分段能明显降低永磁体涡流损耗;负载工况下改变槽口宽度,永磁体涡流损耗几乎没有变化;增大气隙厚度虽然能降低永磁体损耗,但是效果并不明显;同时,更改槽口和气隙厚度会使电感发生变化,并进而影响电机的运行性能。     

Efficiency Optimization of a 100-W 500 000-r/min Permanent-Magnet Machine Including Air-Friction Losses

This paper proposes a method for the efficiency optimization of ultrahigh-speed permanent-magnet machines. Analytical methods are applied for the modeling of the machine that is equipped with a diametrically magnetized rotor and a slotless stator. The outer dimensions of the machine are design constraints, and the internal dimensioning is optimized for minimum losses. The air-friction losses are taken into account in addition to the usual iron, copper, and eddy-current losses. Laminated silicon-iron or laminated amorphous iron is used as the stator core material. The results show that air-friction losses influence the optimum design considerably, leading to a small rotor diameter at high speeds. The loss minimization and the amorphous iron core make it possible to reduce the calculated losses by 63% as compared to a machine design not considering air-friction losses. The resulting efficiency is 95% for a 100-W 500 000-r/min machine excluding bearing losses. Experimental results are shown to illustrate the validity of the method.     

有界波电磁脉冲模拟器参数对传播模式的影响

为了从数量上获得有界波电磁脉冲模拟器的各种参数对其工作区间内电磁波传播的影响程度,基于时域有限差分法建立了有界波电磁脉冲模拟器的数值分析模型,并利用建立的模型计算了模拟器参数对电磁场分量的相对大小和电磁波传播模式的影响。结果表明:增大工作区间的长度和宽度可使得电磁波越来越近似于横电磁波模传播,宽度影响效果尤其明显;有耗大地的介电常数基本不影响电磁波传播模;横向方向的电场分量随着有耗大地电导率的增大而逐渐增大。所以工作区间的宽度和有耗大地的电导率是影响电磁波传播模式的主要因素,这对电磁脉冲模拟器设计具有重要的指导意义。     

Design of a spotsize-converter-integrated laser diode (SS-LD) witha lateral taper, thin-film core and ridge in the 1.3-μm-wavelengthregion based on the 3-D BPM

In order to develop spotsize-converter-integrated laser diodes (SS-LDs) with high efficiency and large-misalignment tolerances in the 13-μm-wavelength region, spotsize converters (SSCs), which consist of lateral taper, thin-film core and ridge, are investigated employing the three-dimensional (3-D) semivectorial finite-difference beam propagation method (FD-BPM) with nonequidistant discretization. The sum of the spot-conversion loss and coupling loss between the laser diode (LD) eigenmode and the single-mode fiber (SMF) eigenmode are calculated for various structural parameters. Small loss of around 1.5 dB can be achieved by introducing a nonlinear taper. The fabrication tolerances for the SSCs are also clarified. The calculated results agree well with the results for actually fabricated SS-LD's. It is also shown that the radiation loss and coupling characteristics of the SS-LDs with a buried thin-film core structure can be improved using a nonlinear taper     

临界模式Boost功率因数校正电路中电感损耗的分析与比较

介绍了临界模式功率因数校正电路的工作原理和特点.通过对电感损耗的分析发现,高频电流在磁芯气隙附近产生的邻近磁场会在电感绕组上产生较大涡流损耗.避免在气隙附近绕线可以减少这种涡流损耗.根据绕组分布方式不同设计了5个电感,应用于200W的PFC样机上,通过实验比较,验证了这种新的绕组布置方法的优越性.     

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.     

高压自耦变压器的涡流损耗计算与屏蔽措施

为应对大型电力变压器漏磁场及杂散损耗问题,采用三维非线性涡流场有限元分析方法,以1台高压自耦变压器为研究对象,引入B-H曲线来描述非线性材料的磁特性,对变压器结构件进行了漏磁场及涡流损耗计算。采用屏蔽措施之前,油箱及夹件等结构件涡流损耗及涡流损耗密度较大,容易引起局部过热问题并且影响变压器正常运行。通过进一步分析,给出了油箱磁屏蔽、夹件L型磁屏蔽和肺叶式磁屏蔽等降低杂散损耗的措施,以及多种屏蔽形式对漏磁场及结构件涡流损耗的影响。结果表明对电力变压器油箱、夹件等结构件采取合理的磁屏蔽措施能够有效地降低杂散损耗并消除热点,不同屏蔽形式对其周围结构件涡流损耗及漏磁场具有不同影响。