Mill motors for adjustable-speed AC drives

The use of AC adjustable-speed drives for rolling mill applications is addressed. AC motor characteristics and how they relate to adjustable-speed mill drives are described. A review of AC motor theory highlighting distinctions between induction and synchronous machines along with comparisons to DC motor performance is included. Constant power speed range performance and limitations, damper winding requirements, and the selection of motor variables such as terminal voltage and frequency are discussed     

Output filters for PWM drives with induction motors

When an induction motor is energized from a pulse width modulated (PWM) inverter, through long connecting cables, its insulation system can be severely stressed. The high dv/dt voltage pulses at the output of the inverter cause traveling waves in the connecting cable between the inverter and the motor. When the traveling wave reaches the motor, a large impedance mismatch is present which leads to a reflected voltage wave that, when added to the incoming incident wave, can reach two times the inverter output voltage. The resulting overvoltage at the motor terminals stresses the insulation system and can lead to reduced motor life. Various output filter arrangements can be used to condition the inverter output voltage before it is applied to the cable. The advantage of adding output filtering is that the dielectric stress on the motor insulation and the inverter cable charging current can both be reduced. The major disadvantages of adding filtering is that they represent extra cost, they require extra mounting space, and they introduce extra losses in the system. The most commonly used types of inverter output filters are: simple output line inductors; output limit filter; sine wave output filter; and motor termination filter. These filters are discussed     

间接矩阵变换器-双异步电机调速系统的简化模型预测控制

间接矩阵变换器-双异步电机调速系统开关状态数量多,数学模型复杂,如果采用传统模型预测磁链控制方法,系统计算量巨大,控制频率及开关频率低,导致网侧电能质量和电机调速性能差.针对这一问题,本文提出一种简化的模型预测电压控制(MPVC)方法,以间接矩阵变换器的输入电流和输出电压作为控制目标,对预测模型进行简化,通过状态预筛选...     

The voltage-frequency relationship for inverter fed induction motor drives

Contents The voltage-frequency relationship and its influence on the losses in the inverter fed induction motor drive is investigated. It is found that the control condition yielding minimum losses very nearly coincides with the control condition requiring minimum motor current for a particular load and speed, and it is shown that there exists an optimum voltage vs torque relationship applicable to all frequencies.

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Der Spannungs-Frequenz-Zusammenhang für einen wechselrichtergespeisten Induktionsmotor-Antrieb

Übersicht Der Spannungs-Frequenz-Zusammenhang und sein Einfluß auf die Verluste eines wechselrichtergespeisten Induktionsmotor-Antriebs wird untersucht. Es wird gefunden, daß der Regelungszustand, der minimale Verluste ermöglicht, näherungsweise mit einem minimalen Effektivstrom für eine beliebige Last und Geschwindigkeit übereinstimmt. Es wird auch gezeigt, daß ein optimales Spannungs-Drehmoment-Verhältnis besteht, das für alle Frequenzen gilt.

     

Saturation model for squirrel-cage induction motors

An induction motor model which includes stator leakage reactance saturation, rotor leakage reactance saturation and magnetizing reactance saturation is presented. This improved model is based on experimental data from 96 motors. The power range of the motors is between 11 and 90 kW. The effects on the torque–speed and current–speed curves of each kind of saturation have been studied. In addition, the parameters of magnetizing reactance saturation and stator leakage reactance saturation have been studied for each motor, and an average value and its dispersion for each parameter are given. This model is considerably more accurate than other models. In particular, it explains the significant differences between theoretical and experimental torque–speed curves in the braking regime (s > 1).     

Grid models intended for investigating electric drives based on induction motors

A model of an electric drive and a grid model of an electric motor are presented. The grid model is used for forward substitution into equations of motion and the calculation procedure intended for calculation motion performance taking into consideration the electromagnetic torque is given. The electromagnetic torque is determined via a static analysis of the grid model of the induction motor operating as a stepper drive or as a drive of a dc brushless motor.     

变频调速异步电动机铁耗的分析计算

本文提出一种计算变频调速异步电动机铁耗的方法，该方法从铁耗模型出发，结合变频器控制特点，推导出谐波铁耗的计算公式，从而可以简单地计算变频器供电下异步电动机的铁耗的大小。并通过实验证实了该方法的正确性。     

感应电动机调压节能的理论分析

详细分析了感应电动机在调压情况下的工作原理 ,得到了功率因数与转差率以及转差率与电机定子电压的关系 ,进而得到功率因数与定子电压的函数关系 ,在此基础上建立了调压时感应电动机节能的数学模型。通过算例在理论上证明了调压节能的可行性 ,为电机节能控制奠定了理论基础     

感应电动机调压节能的理论分析

详细分析了感应电动机在调压情况下的工作原理,得到了功率因数与转差率以及转差率与电机定子电压的关系,进而得到功率因数与定子电压的函数关系,在此基础上建立了调压时感应电动机节能的数学模型.通过算例在理论上证明了调压节能的可行性,为电机节能控制奠定了理论基础.     

三相交流电压相位同步检测电路

介绍了用光耦器件与二极管构成的三相交流电压相位同步检测电路,它可替代笨重的变压器式检测相位方式,提高检测精度和稳定性,拓宽了同步范围,并实现了低成本、低能耗。     

基于人工神经网络的交流感应电机控制系统

讨论了用径向基函数网络(radialbasisfunction,简称RBF)方法所设计的交流异步电机直接转矩控制系统的自适应电机的u-n模型。该模型实时性好,能够克服电机在低速状态下定子电阻的变化及参数变化所带来的影响。仿真表明所设计的系统具有良好的控制性能。     

Early detection of stator voltage imbalance in three-phase induction motors

Online health monitoring of electric motors is of paramount interest to various applications. As the operation of industrial processes becomes more complex, the cost of health monitoring increases dramatically. To this end, much efforts have been directed towards enhancement of fault diagnostics and prognostics in electric motors, largely based on conventional signal processing and pattern classification. This paper formulates and experimentally validates a recently reported technique, called Symbolic Dynamic Filtering (SDF), for early detection of stator voltage imbalance in three-phase induction motors. The SDF-based imbalance detection algorithm is built upon the principles of wavelet transforms and symbolic time series analysis.     

Revolving-field polygon technique for performance prediction of single-phase induction motors

This paper presents a new analytical technique for improving the performance prediction of single-phase induction motors, especially capacitor motors. The technique uses the split-phase motor electrical equivalent circuit analysis together with electrical and magnetic parameters whose variation is computed from the equivalent balanced polyphase motor, so that the same magnetic circuit analysis can be used for both. (The term split-phase is used to cover motors operating from a single-phase supply but with the phase windings split into two orthogonal windings, one of which may have a capacitor in series with it during running or starting.) The technique accounts for the elliptical envelope of the magnetizing field vector and results in improved precision, since the three-phase electromagnetic model is considered to be more precise than the normal split-phase motor analysis. An important result is the computation of vector polygons of flux density for each section of the magnetic circuit, providing a better basis for core loss prediction. The double-frequency torque ripple is also obtained from the stator magnetomotive force and flux-density polygons. Three different electrical equivalent circuit methods for the split-phase motor (based respectively on the cross-field theory, forward- and backward-revolving fields, and symmetrical components) are evaluated to determine the method best suited for incorporating the variation of the circuit parameters from the polyphase magnetic circuit analysis, and it is discussed how the core losses can be included in these circuits to obtain the best overall performance prediction.     

Life prediction modeling of bus capacitors in AC variable-frequency drives

Aluminum electrolytic capacitors are the leading choice for ac variable-frequency drive (VFD) bus filters. Predicting the expected life of these components in this application is complicated by four factors. First, the electrical impedance of aluminum electrolytic capacitors is nonlinear with both frequency and temperature. Second, motor drives produce a spectrally rich ripple current waveform that makes energy loss difficult to compute. Third, the heat transfer characteristic of capacitor banks is dependent on design geometry. Fourth, the expected life of aluminum electrolytic capacitors is extremely sensitive to operating temperature. This paper describes a method for predicting bus capacitor life that addresses these problems by using a multiple component model for capacitor impedance, a motor drive simulation to create ripple current waveforms, a heat transfer model based on bank geometry, and a capacitor life model derived from the device physics of failure. An example is given showing the effect of ac line impedance on the relative expected life.     

Need for industry standards for AC induction motors intended foruse with adjustable-frequency controllers

With the increased use of AC induction motors on adjustable-frequency controls (AFCs) offered in a wide variety of types, there is a need to develop industry standards to provide the guidance necessary for the proper selection of the motor, which will function as intended with the control. These new standards should establish requirements for both electrical and mechanical characteristics of the motor necessary to establish uniformity within the industry. The items that must be covered by such industry standards in order to assure successful applications on adjustable frequency are discussed. Proposals for the content of the standards are presented     

Analysis model of leakage current in a long shield power cable in inverter‐fed AC drives

Each time switching occurs, a PWM inverter produces high‐frequency leakage currents flowing through stray capacitors. Since the inverter for a trash conveyance crane is installed far away from the motor, the shield power cables between them become long, and leakage currents pass through the stray capacitances of the shielded cables and flow to the ground. This paper proposes a model circuit for analyzing leakage currents which flow into the shields of the cables. The effectiveness of the proposed model circuit is verified by comparison of simulated leakage currents using the proposed method and measured leakage currents. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(2): 65–72, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.2002     

双馈风电机组高电压穿越问题综述

针对现代电网规范要求风电机组必须具备故障穿越能力,研究了现代风电并网规范,给出各国高电压穿越准则并进行相应的比较分析.以当今最为流行的双馈风力发电机组为例,分析电网电压骤升时的暂态特性并综述现有的高电压穿越技术方案,从改进的控制策略和增加硬件电路两个方面进行阐述,指出高电压穿越技术未来的发展趋势.     

无轴承异步电机数学模型与解耦控制

针对无轴承异步电机是一个强耦合的非线性复杂系统,实现其电磁转矩和径向悬浮力之间的成功解耦是电机稳定悬浮工作的关键问题.在给出了无轴承异步电机径向悬浮力产生原理的基础上,推导了径向悬浮力和电机旋转部分的数学模型,并采用转子磁场定向控制策略设计了无轴承异步电机矢量控制系统,利用Matlab/Simulink工具箱对该控制系统进行了仿真.仿真试验表明,该控制系统不仅可以实现转子稳定悬浮,而且实现了径向悬浮力和旋转力矩之间的解耦控制,电机具有良好的动、静态性能.