基于三相感应电机的小型化超低频发射天线研究

针对低频电磁传输中天线尺寸过大的问题，设计了一种基于三相感应电机的小型化超低频发射天线.电机工作时产生了时变低频电磁场，可作为超低频发射天线.为有效分析其电磁场分布，文章建立旋转磁偶极子数学模型以等效电机内部旋转时产生的磁场.首先，对电机内部磁场和旋转磁偶极子的关系进行阐述，利用麦克斯韦方程组，得到旋转磁偶极子的电磁场分布.其次，通过电磁仿真软件验证旋转磁偶极子的近场分布特性和远场辐射特性.最后，通过实验对电机近场的磁场分布进行验证.仿真和实测结果表明，三相感应电机具有超低频天线的辐射特性.     

基于VB的电机旋转磁场模拟实现

旋转磁场是电机理论教学中的重要教学内容。通过分析三相交流电机内部磁场的实际运动情况,采用功能强、效率高的编程工具VisualBasic,结合多媒体技术,制作了一套完整的旋转磁场动态演示系统。文中介绍了演示系统的设计思路、软件结构以及实现方法。演示系统具有很好的交互性和生动性,能够形象直观地描述三相对称交流电流与三相交流电机内部旋转磁场的关系,展示出三相交流电机内部磁场的实际运动情况。     

AD2S82A在交流伺服控制中的应用

三相交流伺服电机的精确控制是整个伺服控制系统的关键问题。本文阐述了用R／D转换器AD2S82A完成三相交流电机(测速电机为旋转变压器方式)的转动方向、速度和精度的控制方法及实现过程。     

一种新颖的双三相感应电机缺相运行矢量控制

双三相感应电机的绕组开路后,运用传统的旋转坐标变换,不能实现转子磁场定向矢量控制。本文推导出不对称绕组结构的解耦旋转坐标变换,并提出了一种基于不对称绕组结构的转子磁场定向矢量控制新颖策略,运用PI调节器,使得定子侧谐波电流最小化,降低定子侧谐波损耗。在MATLAB MATLAB/Simulink仿真软件下,建立相应的仿真模型,仿真结果验证本文所提出控制策略的正确性和有效性。     

基于PLC的电机基本控制电路设计

主要讲述了PLC的基本知识以及基于PLC技术的电机三相异步正反转控制电路的设计,设计通过改变三相电源相序,实现了电动机的正反转控制,但自动化程序不高,控制中仍存在需要改进的地方。     

基于单片机AT89C51的直流电机PWM调速系统

文章设计了以单片机AT89C51和L298控制的直流电机脉宽调制(PWM)调速系统.主要介绍了用单片机软件实现PWM调整电机转速的基本方法,给出了程序流程图、KeilC51程序以及Proteus的仿真结果.硬件电路实现了对电机的正转、反转、急停、加速、减速的控制以及PWM的占空比在四位LED上的实时显示.     

空间电压矢量形成旋转磁场的原理分析

本文分析了空间电压法在不同开关状态下的电路联接情况,以及开关状态按一定规律变化时三相绕组电压的变化规律,得到每相电压的交变性和三相电压的对称性。笔者根据每相绕组电压变化规律,按电路暂态分析的方法分析出其电流及磁场的变化规律,分析了开关变化速度对旋转磁场强弱和磁场旋转速度的影响,论证了零矢量分割法插入减少磁场波动的原理和调整磁场旋转速度的原理。     

浅谈单相异步电动机的反转

单相异步电动机是由单相交流电源供电的旋转电机，其定子绕组为单相。当接入单相交流电时，它在定转子气隙中会产生一交变脉动磁场，所以单相异步电动机不能自启动。为了使单相异步电动机自启动，就要在启动时产生一个旋转磁场。本文以电容分相式单相异步电动机为例，介绍单相异步电动机的反转。要使单相异步电动机反转，关键在于改变旋转磁场的旋转方向，但又不能像三相异步电动机那样靠掉换两根电源线来实现。本文结合电容分相式单相异步电动机的具体电路形式，讨论了使其反转的三种方法，经实验验证。确实可行。     

耦合腔行波管PPM聚焦系统横向磁场分析

借助三维静磁场分析软件,模拟仿真了两种非旋转对称PPM聚焦系统的内部磁场：极靴耦合槽分别呈180°和0°排列。根据仿真结果分析了阿良莫夫斯基关于PPM聚焦系统磁场实验中的横向磁场成因;总结了铁制加载头对PPM聚焦系统横向磁场的改善效果以及对磁饱和的影响。最后归纳出横向磁场的3种成因,分别阐述了铁制加载头对其影响;给出了...     

转速/磁链双闭环矢量控制系统的建模仿真

主要研究的是基于矢量控制的转速/磁链双闭环控制对三相交流异步电机进行调速,系统通过交-直-交变频为电机提供三相交流电源。首先对电机的数学模型进行了分析,并在此基础上建立了基于MATLAB/SIMULINK的模块化仿真模型。该系统采用双闭环控制,分别是速度环和电流环。根据仿真结果可看出该方法是可行有效的,这可为电机控制的实际设计提供很好的思想。     

一种新型径向磁浮轴承结构设计与磁场计算

在传统径向电磁轴承中,由于各电磁铁之间磁路相通而使磁场存在相互耦合,这将影响转轴的控制精度和动态响应,为此,提出一种新型的磁铁结构,解决了磁路耦合问题,并缩短了磁路长度.此外,当转子旋转时,磁场极性变化将使转子中产生涡流,此涡流将改变电磁轴承气隙回路中的磁场.利用ANSYS有限元分析软件,以实验样机系统为例,进行了相应的分析和计算.结果表明,随着转速的增加,涡流场将向磁极的后缘和表面集中,电磁吸力减小,而磁阻力增加.实际应用中应尽量选择相对磁导率较大而电导率较小的转子材料.     

E波段折叠波导行波管集成极靴结构设计及仿真

为进一步提升毫米波折叠波导行波管的输出功率,通过整体加工的工艺方法,将折叠波导慢波结构和周期永磁聚焦系统在母材上同时加工,形成一种集成极靴结构。基于圆形注电子光学系统,设计了E波段折叠波导行波管的集成极靴结构。利用三维电磁场模拟软件(CST)的微波工作室,设计并模拟了慢波结构的冷特性参数,并根据慢波结构尺寸设计周期永磁聚焦系统。通过电磁工作环境仿真软件(OPERA)对磁场进行仿真验证,最终整管粒子数值模拟(PIC)计算结果表明,在61~71 GHz频带内可获得大于1 kW的饱和输出功率。该集成极靴结构在提供强轴向磁场的同时,具有结构紧凑、散热性好等优点。     

折叠波导慢波结构特性的研究

应用电磁场仿真软件对折叠波导慢波结构进行理论分析、结构设计和数值模拟。计算和分析了折叠波导的色散特性和散射参量,根据折叠波导特殊结构采用了整体极靴结构。模拟得出了折叠波导的周期磁场,通过调节磁场大小对电子注进行有效聚焦,并得到了电子束在磁场中的运动轨迹。结果表明,折叠波导是一种很适合用作毫米波大功率行波管的慢波结构。     

Modeling of prosthetic limb rotation control by sensing rotation of residual arm bone

We proposed a new approach to improve the control of prosthetic arm rotation in amputees. Arm rotation is sensed by implanting a small permanent magnet into the distal end of the residual bone, which produces a magnetic field. The position of the bone rotation can be derived from magnetic field distribution detected with magnetic sensors on the arm surface, and then conveyed to the prosthesis controller to manipulate the rotation of the prosthesis. Proprioception remains intact for residual limb skeletal structures; thus, this control system should be natural and easy-to-use. In this study, simulations have been conducted in an upper arm model to assess the feasibility and performance of sensing the voluntary rotation of residual humerus with an implanted magnet. A sensitivity analysis of the magnet size and arm size was presented. The influence of relative position of the magnet to the magnetic sensors, orientation of the magnet relative to the limb axis, and displacement of the magnetic sensors on the magnetic field was evaluated. The performance of shielding external magnetostatic interference was also investigated. The simulation results suggest that the direction and angle of rotation of residual humerus could be obtained by decoding the magnetic field signals with magnetic sensors built into a prosthetic socket. This pilot study provides important guidelines for developing a practical interface between the residual bone rotation and the prosthesis for control of prosthetic rotation.      

Scattering by a rotating conducting sphere

The scattering of a plane wave by a rotating sphere with finite conductivity is investigated. The problem is solved by means of the "instantaneous rest-frame" hypothesis. It is shown that a surface current must be taken into account to calculate the jump in the tangential magnetic field at the surface of the sphere, even in the case of finite conductivity. The analytical solution shows that the influence of the rotation becomes negligible in the limit of a perfectly conducting sphere.     

Resistance network analog simulation of the magnetic field produced by a solenoid

A method is proposed for the analog simulation of the magnetic field produced by a solenoid with an arbitrary axially symmetric shape, having magnetic pole pieces also with arbitrary axially symmetric shapes. The ordinary resistance network analog for solving axially symmetric Poisson's problems is used in this method. The simulated magnetic field configurations for some specific cases are compared with theoretical ones. The results obtained by this method can be used directly as the input data for an automatic electron-trajectory tracing scheme in which a resistance network analog is used in conjunction with an electronic computer.     

Design and Simulation of Pole Piece for Focusing of Multi-beam Electron Gun

The design of the aperture in the pole piece of a multi-beam confined-flow electron gun has been studied using the commercially available code OPERA 3D and validated the results using the CST particle studio, and the OmniTrak simulation tools. The results obtained by these tools are in good agreement with respect to the beam-waist radius and the throw of the electron gun. The square aperture proved to be a better option than circular aperture in providing the axisymmetric and uniform magnetic field. The shape and size of the pole piece have been optimized to enhance the laminarity of the electron beam using square aperture.     

Simulation of free-electron lasers in the presence of correlatedmagnetic field errors

The authors address the numerical simulation of field errors that possess statistical correlations. The inevitable errors of actual magnetic wigglers yield a degraded performance of the free-electron laser (FEL) with respect to the performance obtained from ideally modeled magnetic wigglers. The impact of these errors has been theoretically and computationally investigated for simple error modes, in which the field errors have uniform or sinusoidal spatial extent and amplitudes that are statistically independent for each magnet pole piece. These simple models have been recently extended to include more complicated spatial structures and statistically correlated field errors in the analysis of FEL performance. Numerical simulations of the FEL are presented that verify the analytic predictions of the recently extended model