Harmonics in the Squirrel Cage Induction Motor Analytic Calculation-Part Ⅰ: Differential Leakage, Attenuation, Asynchronous Parasitic Torques

The magnetic field generated in the air gap of the cage asynchronous machine and the harmonics of the magnetomotive forces creating that magnetic field, as well as the related differential leakage, attenuation, asynchronous parasitic torques have been discussed in great detail in the literature, but always separately, for a long time. However, systematization of the phenomenon still awaits. Therefore, it is worth summarizing the completeness of the phenomena in a single study – with a new approach at the same time-in order to reveal the relationships between them. The role of rotor slot number is emphasized much more than before. An existing, commonly used, but still impractical basic figure has been modified to more clearly demonstrate the response of the rotor for the harmonics of the stator. The need to treat differential leakage, asynchronous parasitic torques and attenuation together will be demonstrated: new formula for asynchronous parasitic torque is derived;the long-used characteristic curves for differential leakage and attenuation used separately so far was merged into one, correct curve in order to provide a correct design guide for the engineers.

Harmonics in the Squirrel Cage Induction Motor Analytic Calculation Part III: Influence on the Torque-speed Characteristic

The harmonics that appear in the squirrel cage asynchronous machine have been discussed in great detail in the literature for a long time. However, the systematization of the phenomenon is still pending, so we made an attempt to fill this gap in the previous parts of our study by elaborating formulas for calculation of parasitic torques. It was a general demand among those who work in this field towards the author to verify his formulas with measurements. In the literature, it seems,only one detailed, purposeful series of measurements has been published so far, the purpose of which was to investigate the effect of the number of rotor slots on the torque-speed characteristic curve of the machine. The main goal of this study is to verify the correctness of the formulas by comparing them with the referred series of measurements. Relying on this, the expected synchronous parasitic torques were developed for the frequently used rotor slot numbers-as a design guide for the engineer.Thus, together with our complete table for radial magnetic pull published in our previous work, the designer has all the principles, data and formulas available for the right number of rotor slots for his given machine and for the drive system. This brings this series of papers to an end.

CALCULATION OF SATURABLE LEAKAGE REACTANCES OF SQUIRREL CAGE ASYNCHRONOUS MOTORS

A general method of calculating the saturable leakage reactances of squirrelcage asynchronous motors is presented.The method synthesized the variety of effectswhich affect the saturation of leakage magnetic circuit.And the saturable reactances canbe precisely evaluated in any running condition.The computation results of Y-series mo-tors are in good agreement with the test ones.

New Approach to the Power Selection for Asynchronous Motor

The heating calculation of three-phase squirrel- cage asynchronous motor on the condition of starting for a prescribed rotary angle is firstly studied with time dissection method and its corresponding algorithm is provided. Then based upon the algorithm, a new method for motor power selection is established. Motor initial power determined by load power ischecked and modified in terms of time crit erion, heating criterion,and starting torque criterion.An appropriate motor power which meets three criterions is obtained at last, in the meantime, working displacement matrix andfrequency matrix used for control are acquired. Lifting motor of MDJ1800 low-level high- speed palletizer is taken as a reaI case in the paper.

Time-stepping finite element analysis on the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors

To study the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors,a 5.5-kW motor was taken as an example and the multi-sliced field-circuit coupled time stepping finite element method(T-S FEM)was used to analyze the axially non-uniform fundamental and harmonic field distribution characteristics at typical locations in the stator and rotor cores.The major conclusions are:firstly the skewed rotor exhibits a decrease in the harmonic copper losses caused by slot harmonic currents in the stator winding and rotor bars.Secondly,the skewed rotor shifts the non-uniform distribution of field in the axial direction,which leads to more severe saturation and an increase in iron losses.The heavier the load,the more pronounced the increase in iron losses.Furthermore,the influences of different skew angles on motor losses are studied systematically,with skew angles from 0.5 to 1.5 stator tooth pitch.It is found that the lowest total loss occurs at 0.8 stator tooth pitch,and the slot harmonics can be decreased effectively.

三相鼠笼异步电动机无传感器转速检测技术及其适应性

针对三相鼠笼异步电机无位置传感器快速傅立叶变换(fast Fourier transformation,FFT)测速方法需要预先知道转子槽数,且测试精度易受噪声干扰和采集时长等因素的影响,提出一种基于奇异值分解-Prony(singular value decomposition-Prony,SVD-Prony)算法的无位置传感器高精度转速测量技术。运用电机学相关理论,研究转子槽谐波测速机理,并给出整数倍率转子槽数的计算方法。在分析并明确定子电流噪声影响和FFT法存在检测精度受采样时长限制等问题的基础上,研究基于奇异值增长率的SVD滤波方法和用于辨识转子槽谐波的Prony算法,并以Y160M-4型电机为研究对象,在不同运行状态下对该技术的适应性进行分析。在此基础上,构建相关物理测试平台,对YE90S-2型电机进行实测。结果表明,在相同采集情况下,所提方法测试绝对误差仅为FFT测速方法的几分之一,检测精度大幅提高。

三相鼠笼异步电机转子断条故障检测

针对转子断条故障信号易被基波淹没,故障特征不易提取及容易误判等问题,提出在空载低压运行状态下通过基于奇异值增长率的SVD-Prony算法检测转子断条故障。在研究转子断条故障特征及转子槽谐波测速机理的基础上,给出了整数倍转子槽数的理论计算公式及转子断条故障信号频率与转子槽谐波频率的关系表达式,并通过转子槽谐波频率验证转子断条故障信号的正确性,以此提高转子断条故障检测的有效性。通过仿真,验证了所提方法的有效性和实用性,对电机转子断条故障检测研究具有重要意义。

小电网中大型泵用笼型异步电动机的电容补偿起动

本文比较了小电网中大型泵用笼型异步电动机各种起动方式的优缺点 ,提出了并联电容起动的方案 ;给出了一套完整的电机起动参数、并联电容值的计算方法 ;通过计算机仿真得出并联电容后电机端电压、无功电流、功率因数等起动性能的改善 ;

笼型异步电动机径向电磁力波的有限元计算

建立笼型异步电动机的场路耦合时步有限元模型,通过定子相电流仿真波形和实测波形的谐波比较验证有效性。基于该模型计算气隙磁通密度,进而利用经典的Maxwell应力张量法计算径向电磁力。气隙磁通密度和径向电磁力均随空间和时间变化,利用二维傅里叶分析分别求解它们的谐波;并探讨齿槽和转差率对磁通密度和径向电磁力的影响,以及磁通密度波和径向电磁力波之间的关系。将径向电磁力波和实测电磁噪声频谱进行了分析和对比,结果表明径向电磁力波的计算是合理有效的。利用本文方法计算的径向电磁力及其谐波可应用于在设计阶段对电磁噪声的分析。

笼型异步电机转子断条故障引发的电磁力波变化规律

以一台Y80_2-2型笼型异步电机为例,分别建立了正常电机和转子断条电机的二维有限元模型,并对其进行了瞬态磁场计算,得出了时空变化的气隙磁通密度波,并与实验测得的气隙磁通密度值进行了比较。利用瞬态磁场计算出的气隙磁通密度波,基于经典的麦克斯韦应力方程计算了电机正常及断条故障运行时气隙中的电磁力波。综合运用二维快速傅里叶变换,频谱分析比值校正等方法对电磁力波的阶数、频率和幅值进行了计算和分析。同时利用传统公式计算了气隙磁通密度波以及电磁力波的阶数和频率,与数值计算的结果进行了比较,得出了电机断条故障弓I发电磁力波的变化特征。

立式鼠笼异步电动机三维CFD热计算

用来拖动动力设备(如核电设备)的立式鼠笼异步感应电动机,其温升不仅影响电机寿命及其安全性,还影响系统能否正常运行,因而,探究其内部的热流场分布特点,进行完善的热设计非常重要。首先建立三维电动机物理模型,然后基于有限体积法进行电机内部空气湍流流动及传热耦合数值模拟,得到空气三维速度、转子铜条与定子绕组等三维温度分布特征。结果表明:对于额定转速为4000 r/min的立式电机,气隙中空气速度显著大于定子风沟齿部、轭部的速度;沿高度方向,转子铜条温升很小,定子绕组及绝缘、每段定子铁心叠片中的齿部与轭部均为靠近风沟位置处温度低,而靠近铁心段中间位置温度高。模拟结果与实验测量数值误差较小,结果较准,确为同类型立式鼠笼异步电机通风设计提供理论参考。

降低大中型异步电动机电磁噪声的槽配合选取方法

目前为了限制大中型异步电动机的电磁噪声而选用的槽配合主要是基于经验,没有考虑振动模态,有时会导致电磁噪声超标。本文对定转子齿谐波和饱和谐波引起的电磁力波详细理论分析的基础上,给出了考虑定子模态时槽配合选取方法。该方法主要是利用优化转子槽数来合理选取槽配合,以达到限制电磁噪声的目的。以YKK500-10型电机为例,通过两种槽配合的电磁噪声分析和实测结果验证了本文方法限制电磁噪声的有效性。

光伏发电系统利用直流-异步电机并网控制方法的研究

针对光伏并网逆变器存在成本高、故障率高、谐波含量大及控制复杂等问题,提出了一种实用的光伏发电系统利用直流-异步电机并网的方案。该光伏并网系统中直流电机和笼型异步电机同轴旋转,实现直流电能和交流电能之间的转换。由光伏电源为直流电机供电,直流电机拖动异步电机完成电机的起动过程;当电机转速接近同步速时并网开关合闸,实现光伏发电系统的并网运行。光伏系统并网后,通过调节直流电机的端电压实现对异步电机输出有功功率的控制,保证直流母线电压的稳定。在MATLAB/Simulink环境下对光伏电源利用直流-异步电机并网系统进行仿真,仿真结果验证了该方案的正确性和可行性。

采用铸铝转子和铸铜转子时鼠笼式异步电机的损耗特性对比

在超高效电机的研制中,采用铸铜转子是一种提高电机效率的有效方法。为了对比分析铸铝转子与铸铜转子电机的内部损耗特性,本文利用场-路耦合时步有限元法,以1台5.5 kW异步电机为例,计算分析采用铸铝转子和铸铜转子时电机各项损耗及效率的变化特点。结果发现:空载时,2种转子的各项损耗并无太大差别;满载时,定子铜耗和铁耗差别不大,铜转子基波铜耗大幅降低,但谐波铜耗略微增加,最终使得电机总损耗降低约60W,效率增加约1%。

大中型笼型异步电动机电容起动的研究

详细描述了大中型笼型异步电动机电容起动的特点，给出电容初步设计的原则与步骤，建立三相笼型异步电动机电容起动系统的数学模型，并进行仿真计算．理论分析和仿真实例表明，异步电动机采用电容起动，可以明显降低起动电流，保持较高的起动转矩，减少起动时间，是一种可供选择的新型起动力法，值得研究与开发．

一种新型立式鼠笼电机流场数值计算与分析

为了保证电机的可靠性,对电机内流场进行仿真计算十分必要。该文以一台四进两出新型通风方式的鼠笼异步电动机为例,研究气隙及定子三维流场的分布规律。建立了计算域物理模型并给定相应边界条件,基于计算流体动力学原理(computational fluid dynamics,CFD),采用有限体积法进行三维湍流流动数值模拟求解,分析了速度场和压力场的分布规律。结果表明:在压力及旋转剪切力作用下,沿径向气隙、定子风沟齿、轭部界面处空气速度梯度较大;在气隙中、定子风沟齿部空气迎、背风面的静压与速度分布趋势相同,沿周向均呈现周期性变化,周期数等于定子槽数。

异步电机鼠笼转子断条的频谱分析及诊断

介绍了采用定子电流的频谱分析来诊断异步电动机鼠笼转子断条故障缺陷的基本理论， 分析了实际应用中的技术难题和解决方法， 阐明了转子断条诊断在实际生产中的意义。

基于IPM鼠笼式异步电机交流伺服系统

介绍一种以普通鼠笼式异步电机为执行电机的交流伺服系统 ,该系统以 80C1 96KC单片机为核心构成控制电路 ,以智能功率模块 (IPM)组成主电路。介绍了系统软、硬件组成及设计方法。实验结果表明 ,该系统具有十分理想的动静态性能 。

基于P-Q变换的鼠笼式异步电动机转子故障仿真分析

为对电动机进行可靠的实时监测与诊断,提出了基于P-Q变换的鼠笼式异步电动机转子的故障分析方法。该方法是通过同时采集三相电压和电流信号,由电压信号和电流信号相乘得到瞬时有功功率P,将三相电压经过Hilbert变换再与电流信号相乘得到瞬时无功功率Q,以P为横坐标,Q为纵坐标,得到P-Q图。由于正常情况下电动机P、Q均恒定,在P-Q坐标系下对应一个点,而断条故障时电动机频率中将会有附加成分,因而在P-Q坐标系下对应于一个椭圆,通过椭圆长轴的长度分析断条故障的严重性。仿真试验证明,这种方法在轻载情况下仍然有效。

小波包算法在电动机转子断条故障诊断中的应用

采用改进的小波包算法提取故障特征,提出了一种基于频带能量的故障诊断方法。该方法能快速准确地检测转子断条故障。