感应电机转子绕组故障仿真与实验研究

从仿真计算与实验两方面对感应电机转子绕组故障进行研究。首先分析断条数量对电机的影响：讨论了转子断条故障后转子备导条电流以及备段端环电流分布及变化情况，转子断条数量与定子电流中转子绕组故障特征量的关系。转子断条位置对电机影响很大，过去没有引起人们的重视，该文对此进行深入研究，分析电机转子断条位置与故障特征量之间的关系，转子断条位置与转子导条电流、转子端环电流之间的关系，并总结出其规律，指出哪些位置导条进一步断裂的可能性较大。该文还揭示了过去人们试图把故障特征量的大小作为电机转子断条根数多少的判据的局限性，提出了把断条引起电机的不对称性作为电机转子绕组故障程度判据的新的理论。     

绕线式异步电动机同步化后最大转矩及输出无功功率的计算

1 概述在工矿企业中,常采用绕线式异步机同步化的方法,把绕线式转子作适当改接,通以直流电励磁,以改善用电的功率因数。但实践表明,同步化后电机的最大转矩明显下降,如所带有功负载不变,即有可能由于功角太大而造成失步,因而电机的负载必须适当降低。在生产实践中往往通过试验来决定。这样做虽然是必要的,但往往要进行多次。为了使试验更切实际,本文提出了同步化后电机的最大转矩(或容许负载转矩)和可以送出的无功功率的计算方法。     

不同转子结构无刷双馈电机稳态运行特性的对比实验研究

笼型和磁阻转子是无刷双馈电机常用的两种转子结构型式，为了对比研究不同转子结构对该种电机稳态运行特性的影响，研制了具有同一定子和两个不同结构转子的实验样机，并进行了对比实验研究。实验结果表明，各向异性轴向叠片的ALA（Axially Laminated Anisotropic）磁阻转子无刷双馈电机具有较好的同步和双馈调速特性，而笼型转子无刷双馈电机具有较好的起动和异步运行特性。     

关于无功补偿的几个问题

电力网内的无功补偿是节约电能的一项重要措施。下面就无功补偿中的几个问题提出一些看法,以资商榷。一、利用异步电动机同步化作为补偿措施异步电动机同步化就是在通常的绕线式异步电动机,待其启动并接近同步转速后,从它的转子绕组通以直流励磁电流,以同步转速运转。如调节励磁电流,则将与同步机相仿,也调节了电动机功率因数,调节了无功。广东,上海,北京一些厂矿与清华大学等单位先后从理论上作了很多探讨和分析,在利用转子绕组作为励磁绕组的结线上,作了5种结线的比较     

同步化双馈风电并网控制技术

作为风电并网主流机型——双馈风电机组的并网控制日益重要,然而传统矢量控制的双馈风电并网控制,其转子位置角信号容易受到干扰而影响其稳定性,给风电并网带来了影响。分析了双馈风电机组(DFIG)的同步化特点,提出了基于转子电压幅值和频率控制(MFC)的DFIG并网控制方法,并进一步提出了基于MFC控制的含调度指令功能的DFIG并网控制策略;通过仿真验证了基于转子电压MFC的双馈风电并网控制策略的有效性。     

从异步电机同步化的特性探讨其适用条件

所谓异步电机同步化就是将绕线转子异步电机改造成同步电机,即将绕线三相转子绕组改接成直流励磁绕组,并通以直流励磁电流,实现同步运行。它具有起动电流小,起动转矩大的特点,使原来从电网吸收无功功率的异步机改成向电网输出无功功率的同步电动机,特别适应于对起动要求高的泵站。因此,合理使用这项技术是泵站节能挖潜改造的一项行之有效的措施。     

基于实验模态和工作变形的大型风力发电机转子动力学特性分析

对大型风力发电机转子设备静止和旋转状态下的动力学特性进行了实验分析。研究主要基于实验模态分析和工作变形分析，采用LMS.TESTLAB系统及无线数采系统，首先测试各响应点锤击激励下振动信号，信号经频响函数计算、曲线拟合后得到其各阶模态参数；然后进行全转速振动测量，并根据实验结果选取共振运行工况，进行工作变形测试分析；最终实现转子静态及旋转状态数据收集、模态参数提取和分析。分析结果表明：发电机转子在旋转过程中，发生共振的频率与实验模态频率存在偏差，转子整体刚度减小；且在旋转电磁力作用下，振型由静止状态时的驻波形式变为行波形式。该研究结果对于转子动力学评估、仿真模型修正及参数输入以及转子结构优化设计具有借鉴参考意义。     

液压自动平衡技术在风机转子上的应用

提出用液压自动平衡技术解决风机转子运行过程中因结垢造成的动不平衡问题。采用转子动力学软件对风机进行有限元建模。根据平衡头的3个可能安装平面，利用转子动力学软件分别计算虚拟安装在这3个安装平面下的平衡头的平衡效果，找出平衡头的优化安装平面。设计风机转子的模拟实验台并进行液压自动平衡实验。实验表明将液压自动平衡头安装在优化平面上可以实现转子的不停机在线自动平衡，为在风机上应用液压自动平衡技术提供理论参考和实验依据。     

电机铸铝转子压铸充型过程实验研究

针对目前小电机铸铝转子压铸过程中存在的内在质量问题，应用流体力学相似理论，采用高速摄影技术，从理论上研究了转子压铸的水模拟充型过程。     

液体媒质超声波电机运行特性的实验研究与分析

该文介绍了一种基于液体媒质的非接触型超声波电机，其转子浸于液体之中，不与定子直接接触，有效地克服了接触型超声波电机的易磨损、不能长时间连续工作等缺点，是超声波电机领域的一个新的研究方向。结合液体媒质超声波电机的基本结构及运行机理，文中阐述了电机运行过程中将超声振动所产生的能量通过液体传递给转子，从而驱动转子旋转这一能量传递的基本过程，揭示了液体中的雷诺剪切应力是电机声流场的驱动力。然后，用实验测定了电机转速与驱动频率、驱动电压、液体粘性、液位高度和转子半径之间的关系。并对实验结果进行了比较分析，且在此基础上结合本电机的运行机理以及驱动控制系统、液体环境和转子半径等因素对电机转速的影响，对液体媒质超声波电机的运行条件进行了优化分析。     

A Landauer Approach to Nanoscale MOSFETs

A tutorial introduction to the theory of the nanoscale MOSFET is presented. The essential physics is first reviewed by examining numerical simulations. Next, the analytical theory of the ballistic MOSFET is introduced by presenting a simple derivation based on Boltzmann statistics. The extension to Fermi-Dirac statistics is then discussed. To clarify the connection to well-known results from mesoscopic transport, the T _L = 0 K theory is then developed. Finally, qualitative arguments are used to discuss the role of scattering in nano-scale MOSFETs, and the relation of scattering theory to conventional MOSFET theory is examined.     

Minimal axiom group of similarity-based rough set model

Rough set axiomatization is one aspect of rough set study to characterize rough set theory using dependable and minimal axiom groups. Thus, rough set theory can be studied by logic and axiom system methods. The classical rough set theory is based on equivalence relation, but the rough set theory based on similarity relation has wide applications in the real world. To characterize similarity-based rough set theory, an axiom group named S, consisting of 3 axioms, is proposed. The reliability of the axiom group, which shows that characterizing of rough set theory based on similarity relation is rational, is proved. Simultaneously, the minimization of the axiom group, which requests that each axiom is an equation and independent, is proved. The axiom group is helpful to research rough set theory by logic and axiom system methods. __________ Translated from Journal of Fudan University, 2004, 43(5): 856–859 (in Chinese)     

粗糙集理论及应用

粗糙集理论被广泛应用于不确定环境下的信息处理。介绍了粗糙集理论的发展历程、基本原理和基本特点,阐述了粗糙集理论的研究方向和应用领域,比较了粗糙集理论与模糊理论的关系并指出了两者的结合将得到更好的结果。     

A new approach for three-phase loads compensation based on the instantaneous reactive power theory

The original instantaneous reactive power theory or p–q theory has been systematically used in the control of active power filters (APFs). When the APF is connected in parallel to a non-linear and unbalanced load, the p–q theory application has allowed a compensation strategy named constant power to be obtained. This means that, after the APF connection, the instantaneous power supplied by the source is constant and it has the same value as the average power consumed by the load. Nevertheless, the use of other compensation strategies is possible: unity power factor or sinusoidal and balanced supply currents, among others. This paper shows that any compensation strategy may be developed into the p–q theory frame. Besides, the paper presents a p–q theory reformulation without using mapping matrices, which makes easier the obtention of the compensation currents. Finally, an exhaustive analysis of practical cases has been carried out at simulation and experimental level through a laboratory prototype which has allowed the proposed approach to be verified.     

PERFORMANCE CALCULATIONS ON TWO-SPEED SHUNTED CAPACITOR MOTOR BY CROSS-FIELD THEORY

ABSTRACT

The performance equations on two-speed shunted capacitor motors are developed in this paper, using the concepts of cross-field theory. Steps to use these equations to calculate the performance of such motors are suggested. Speed-torque data are calculated, using these equations, and plotted for the purposes of illustration. An exact agreement between this theory and another existing theory is obtained     

Comparison of instantaneous reactive power <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">q</Emphasis> theory with theory of the current's physical components

The comparison of the instantaneous reactive power (IRP) p-q theory with the theory of the current's physical components (CPC) presented in this paper provides the relationship between powers in both theories applied to three-phase, three-wire circuits with sinusoidal voltages and currents. It shows that results of the instantaneous reactive power p-q theory are inconsistent with power phenomena in such circuits. Namely, the IRP q may occur in circuits with linear, purely resistive loads thus, with zero reactive power, Q, and the instantaneous active power p may occur in circuits with purely reactive loads, thus, with zero active power, P. Consequently, the IRP p-q theory fails to identify the power properties of three-phase circuits with unbalanced loads. Moreover, in spite of sinusoidal supply and the lack of distortion, the IRP p-q theory suggests that the active and reactive currents contain a third-order harmonic. Also the IRP p-q theory is not capable of providing information on power properties of the load instantaneously.     

Comparison of classical nucleation theories with monte carlo simulations of ising models

Abstract

We present Monte Carlo results for switching in two and three dimensional Ising models in order to compare with classical nucleation theory. For the case of step-function voltage pulses classical nucleation theory correctly predicts the Monte Carlo results including a cross-over from a thermal nucleation to heterogeneous nucleation due to quenched defects. For triangular wave voltage pulses the coercive field depends on the sweep rate logarithmically roughly as predicted by classical nucleation theory. However the power law dependence on the logarithm of the sweep rate is significantly different from the classical nucleation theory prediction.     

The theory of instantaneous power in three‐phase four‐wire systems and its applications

This paper discusses “the p–q theory” and “the cross‐vector theory” in three‐phase four‐wire systems, with the focus on similarities and differences between the two theories. They are perfectly identical if no zero‐sequence voltage is included in a three‐phase three‐wire system. However, they are different in definition of the instantaneous active power and instantaneous reactive power in each phase if a zero‐sequence voltage or current is included in a three‐phase four‐wire system. Based on both theory and computer simulation, this paper leads to the following conclusions: An instantaneous reactive‐power compensator without energy storage components can fully compensate for the neutral current even in a three‐phase four‐wire system including a zero‐sequence voltage or current, when a proposed control strategy based on the p–q theory is applied: However, the compensator cannot compensate for the neutral current fully, when a conventional control strategy based on the cross‐vector theory is applied. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 74–86, 2001     

Beitrag zur Theorie der Permanentmagnete

Übersicht Ausgehend von der Elementarstromtheorie der Molekularmagnete des Permanentmagneten wird gezeigt, daß die Ersatzstrom-und die Magnetmengentheorie sich aus dieser ableiten lassen und auch im Inneren des Permanentmagneten gültig sind, wo sie zu identischen magnetischen Feldstärken führen. Die landläufig als magnetische Feldstärke im Inneren des Permanentmagneten bezeichnete Größe ist dabei der Anteil der Entmagnetisierungsfeldstärke.

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Contribution to the theory of permanent magnets

Contents Starting from the elementary current theory of the permanent magnet, it is shown in this paper that the substitution current and the magnet mass theory are all derivable from the elementary current theory and are also valid inside the permanent magnet, where they become identical magnetic field strengths. The value commonly known as the magnetic strength inside the permanent magnet is therefore the demagnetization field strength.

     

变极理论在大型循环泵电机节能改造中的运用

介绍了利用变极理论，实现大型电动机节能的原理和在实际改造后取得的节能成果。并对循环泵电机利用此原理进行改造后，将取得的节能效果进行了预测。