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.

Cascaded Model Predictive Control of Six-phase Permanent Magnet Synchronous Motor with Fault Tolerant Ability

In the field of high-power electric drives, multiphase motors have the advantages of high power-density, excellent fault tolerance and control flexibility. But their decoupling control and modulation process are much more complicated compared with three-phase motors due to the increased degree of freedom. Finite control set model predictive control can reduce the difficulties of controlling six-phase motors because it does not require modulation process. In this paper, a cascaded model predictive control strategy is proposed for the optimal control of high-power six-phase permanent magnet synchronous motors. Firstly, the current prediction model of torque and harmonic subspaces are established by decoupling the six-phase spatial variables. Secondly, a cascaded cost function with fault-tolerant capability is proposed to eliminate the weighting factor in the cost function. And finally, the proposed strategy is demonstrated through theoretical analysis and experiments. It is validated that the proposed method is able to maintain excellent steady-state control accuracy and fast dynamic response while significantly reduce the control complexity of the system. Besides, it can easily achieve fault-tolerant operation under open-phase fault.

A New Switching Sequences of SVPWM for Six-Phase Induction Motor with Features of Reduced Switching Losses

In this paper,new SVPWM switching sequences for six-phase asymmetrical induction motor drives are derived with the aim to reduce inverter’s switching losses.Total three switching sequences are introduced in this paper.These sequences are derived such that the phases get continuously clamped when a current of the phases is around its peak magnitude and hence reduced switching losses are recorded.The comparative performances of these modulation techniques are studied with two existing switching sequences.Simulation,analytical and experimental results are presented.Based on these results,it is found that new switching sequences reduce switching losses effectively in dual three phase inverters.

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.

Modeling and Simulation of High-Voltage Asynchronous Motor Voltage-Regulator

For starting high-voltage asynchronous motor,the voltage regulator based on current-limiting transformer is presented in the paper. Its mathematical model needs to be established analyzing and designing voltage regulator of high-voltage asynchronous motor. The mathematical model of the current-limiting transformer is deduced based on basic circuit theory. It can be found that a continuous variation reactance can describe the current-limiting transformer during starting process. The two variables functions of current and voltage are transformed into one-variable functions,and thus system control is greatly simplified. The voltage regulator is simulated on the basis. The simulation results show that this model has enough accuracy. Finally, the high-voltage asynchronous motor voltage regulator based on current-limiting transformer is designed and tested on this model.

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.

Comprehensive Energy-Saving Optimization Model of Asynchronous Motor for Voltage Regulation Based on Static Synchronous Compensator

There are several problems existing in the direct starting of asynchronous motor such as large starting current,reactive power absorption from network side and weak interference-resistance,etc.Aiming at this,a comprehensive energy-saving optimization model of asynchronous motor for voltage regulation based on static synchronous compensator(STATCOM)is put forward.By analyzing the working principle and operation performance of static synchronous compensator regulating voltage,a new energy-efficient optimization method for asynchronous motor is proposed based on the voltage regulator model to achieve soft start,continuous dynamic reactive power compensation and the terminal voltage stability control.The multi-objective optimal operation of asynchronous motor is realized by controlling the inverter to adjust the reactive current dynamically.The strategy reduces the influence of starting current and grid voltage by soft starting,and realizes the function of reactive power compensation and terminal voltage stabilization.The effectiveness and superiority of the proposed model is verified by the simulation analysis and the results of comparison with the motor started directly.

Frequency control system based on power factor control of asynchronous motor

Deduced the relationship between the power factor (PF) and the angular fre-quency according to the simplified equivalent circuit of asynchronous motor, forming a power factor auto-control system. An anti-interference circuit was also introduced in the middle voltage link of inverter to avoid the shift of the optimum PF point caused by the change of the load and the reliable run of the control system was assured. The experi-ment results show that it has a good self-adaptation in the whole scope of speed ad-justment and an obvious economization on energy while it runs under load.

Research on Open-circuit Fault Tolerant Control of Six-phase Permanent Magnet Synchronous Machine Based on Fifth Harmonic Current Injection

This paper proposes a novel control approach for fault-tolerant control of dual three-phase permanent magnet synchronous motor(PMSM) under one-phase open-circuit fault.A modified six-phase static coordinate transformation matrix and an extended rotating coordinate transformation matrix are investigated considering the influence of the fifth harmonic space on fault-tolerant control. These mathematical models are further analyzed in the fundamental space and the fifth harmonic space after the fault and to eliminate the coupling between the d-q axis voltage equation in the fundamental wave space and the d-q axis voltage equation in the fifth harmonic space, a secondary rotation coordinate transformation matrix is proposed. To achieve the purpose of reducing torque ripple, the fault-tolerant control method proposed in this paper not only takes the minimum copper loss as the constraint condition, but also injects the fifth harmonic current. The experimental result of current and torque is used to verify the accuracy of fault-tolerant control.

基于开口变压器法的交流电机定子非激励相绕组匝间短路检测研究

为了解决交流电机定子绕组中线圈绝缘损伤引起匝间短路故障无法准确、快速定位的问题,提出将检测转子绕组匝间短路的开口变压器法移植到检测交流电机定子绕组匝间短路,定子单相添加激励源,非激励相绕组设置故障点,开口变压器检测故障点所在槽,分析故障前后开口变压器绕组感应电动势的变化。首先阐述开口变压器检测定子非激励相的工作原理,分析正常和故障状态下通过开口变压器铁心漏磁通的表达式,进一步得到开口变压器绕组感应电动势表达式,获取故障变化规律。随后建立交流电机电磁仿真模型,进行仿真分析,最后用一台定子样机进行实验验证。结果表明:故障状态下,随着故障程度的加深,故障点所在槽的开口变压器感应电动势随之减小,证明了开口变压器可以作为离线检测交流电机定子非激励相绕组匝间短路故障的有效手段。

考虑用电和馈电模式的变流器电驱系统建模与稳定性分析

由大量异步电机驱动设备构成的电力电子化交流配用电系统存在严重的次/超同步振荡问题。电驱系统正常工作时具有用电和馈电2种运行模式,现场振荡现象表明不同的运行模式对系统的稳定性影响也不同。建立了含机侧系统的电驱系统详细阻抗模型,利用阻抗分析法揭示了电驱系统接入电网的次/超同步振荡机理,分析了运行模式、电网强度、控制参数、交流电压幅值等因素对系统次/超同步稳定性的影响,并基于相位裕度灵敏度明确了主导影响因素。基于实际系统数据,搭建了时域仿真模型,仿真复现了振荡现象,并验证了理论分析的正确性。

基于三相异步电动机维修操作技术的研究

三相异步电动机应用广泛,其维修核心嵌线技术特殊又不易掌握。理论电动机绕组展开图与实际操作习惯不是很吻合,为方便学员高质量依图施工掌握嵌线技术,改进电动机绕组展开图起始槽为第一槽、改进绕组头尾处在有效边所在槽位、改进绕组电流方向为一实际瞬间方向;改进电动机完整维修技术为五个技术模块。实践证明改进的方法效果好效率高,维修后的电动机性能稳定,初学者在改进方法下能高效快速掌握电动机维修技术。

基于高频电流信号的电机故障特征提取方法

目前异步电机故障诊断主要依赖于振动、温度和噪声等参数,对于监测的电气信号,主要用于分析电机输出动力情况。电气信号中除了体现电机动力输出特征外,还包含丰富的机械故障、电气故障等信息特征。由于电气信号中的故障特征信号微弱,易被基频分量与噪声湮没而难以突出故障特征,不利于电机状态监测与故障诊断,因此提出了一种基于高频电流信号解调的电机故障特征提取方法,针对采样率不低于25.6 kHz的电机定子高频电流信号,综合运用高通滤波、Hilbert变换、快速傅里叶变换(FFT)3种分析方法,提取高频电流中电机故障的微弱特征信号,应用神经网络算法对电机正常、静态偏心、动态偏心、转子断条、轴承内圈、轴承外圈6种状态进行了诊断。该方法准确提取了电流信号故障特征,并成功识别了6种故障。

基于离线单相周期方波脉冲的三相异步电机启动转矩测试

为了克服三相异步电机启动转矩无载测试现有方法存在的测试精度较低、电网冲击等问题,提出一种基于离线单相方波脉冲的电机启动转矩测试方法。以Y160M-4型三相异步电机为研究对象,给出用于测试启动转矩的单相方波逆变电源结构、工作原理及关键参数计算方法,并利用二维瞬态电磁场数值计算方法,以研究不同激励模式下的启动转矩为目的,获取电机启动过程的电枢电流。结合电机数学模型和坐标变换理论,研究并给出单相正弦波激励下的电机等效电路模型和启动转矩理论计算模型。在此基础上,进一步给出单相方波激励下的启动转矩数据处理方法。经验证,依据所提出的单相方波激励下的电机启动转矩计算方法并结合二维瞬态电磁场数值仿真,启动转矩测试相对误差约为0.25%。研究结果表明,利用该方法计算三相异步电机的启动转矩,测试精度获得明显提高,从而证明了所提方法的正确性和可行性。

基于VMD⁃ESA和IPOA⁃XGBOOST相结合的异步电机故障诊断

为了提高异步电机故障诊断的准确度,提出一种结合变分模态分解(VMD)、包络谱分析法(ESA)和改进的鹈鹕优化算法优化的极限梯度提升模型(IPOA‐XGBOOST)的智能诊断方法。首先,对实测的异步电机振动信号进行VMD分解,并用ESA计算VMD分解得到的本征模态分量(IMFs)的瞬时能量矩阵;然后用奇异值分解法(SVD)对得到的瞬时能量矩阵进行特征提取;最后,使用提取到的特征向量训练IPOA‐XGBOOST模型,得到异步电机的故障诊断准确率。另外,为了解决鹈鹕优化算法容易陷入局部最优解、寻优速度慢等问题,使用Circle映射改进鹈鹕优化算法。将改进的鹈鹕优化算法、遗传算法(GA)和鹈鹕优化算法进行寻优分析,实验结果表明,改进的鹈鹕优化算法的寻优效果最好。

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。

一种基于离散变频的三相异步电机软启动控制

针对传统三相异步电机软启动方式存在启动转矩不足,难以适用于部分需要重载启动电机场合的问题,采用一种离散变频的软启动控制方法,将离散变频的方式与传统软启动控制相结合,同时加入功率因数角补偿以提高电机在启动过程中的平稳性。实验表明,该控制方法可在抑制电机启动电流的同时,有效提升电机的启动转矩,同时抑制电机在启动过程中的抖动。

迁移学习和CNN的电机故障诊断方法

针对缺乏数据导致卷积神经网络(Convolutional neural networks,CNN)训练不佳的问题,以三相异步电机故障诊断为研究对象,提出了基于迁移学习和CNN结合的电机故障诊断方法。首先搭建了电机故障诊断实验平台,通过加速度传感器获取CNN模型带标签数据,通过训练获取预训练模型;然后结合迁移学习得到的预训练模型迁移到目标域,并通过对目标域的带标签数据进行训练以优化CNN参数;最终获得可以对目标域数据有着良好分类能力的新模型,从而实现目标域带标签数据稀少情况下的电机故障诊断工作。通过将该方法与传统CNN、变分模态分解(Variational modal decomposition,VMD)-支持向量机(Support vector machine,SVM)、VMD-K近邻(K nearest neighbor,KNN)以及VMD-BP神经网络等识别模型进行对比验证,结果显示本文提出的迁移CNN模型模式识别方法有更好的识别效果。