AI techniques in induction machines diagnosis including the speedripple effect

Various applications of artificial intelligence (AI) techniques (expert systems, neural networks, and fuzzy logic) presented in the literature prove that such technologies are well suited to cope with on-line diagnostic tasks for induction machines. The features of these techniques and the improvements that they introduce in the diagnostic process are recalled, showing that, in order to obtain an indication on the fault extent, faulty machine models are still essential. Moreover, by the models, that must trade off between simulation result effectiveness and simplicity, it is possible to overcome crucial points of the diagnosis. With reference to rotor electrical faults of induction machines, a new and simple procedure based on a model which includes the speed ripple effect is developed. This procedure leads to a new diagnostic index, independent of the machine operating condition and inertia value, that allows the implementation of the diagnostic system with a minimum configuration intelligence     

Analysis of three-phase induction motors utilizing `The IodekiceLocus'-a normalized impedance circle

A method that allows students to analyze the performance of any three-phase induction motor operating at any arbitrary speed, either analytically or graphically, using the same conceptual approach is presented. The method uses a unity-diameter normalized impedance circle with a periphery calibrated in terms of normalized slip, which is defined as the ratio of per unit slip to a readily determined machine constant. Equations that allow the tabulation of the real and imaginery impedance components of the normalized circle as a function of normalized slip are developed. These data may be plotted for use with graphical analysis or used directly in a simplified mathematical analysis. The key factor in the development is shown to be the concept of normalized slip. Using this concept, the specific operating point of a machine can be simply and uniquely determined for any given value of per unit slip     

混合励磁盘式电机的有限元分析

为了扩大转速范围 (恒压发电 /电动调速 ),文章介绍一种新型的磁场可控的混合励磁盘式电机,并以一台样机模型为例,用三维动态有限元进一步验证该电机的工作机理与磁场控制的特性。     

Monitoring of induction Machines by maximum covariance method for frequency tracking

Several techniques were presented in the literature in order to perform accurate tracking of frequencies for different purposes. Most of them are modified versions of the traditional discrete Fourier transform (DFT) or other spectrum-estimation techniques. This paper presents a procedure based on the statistical analysis of the current signal in the time domain, referred to as maximum covariance method for frequency tracking (MCMFT), which allows to obtain high-frequency resolution independent of the sampling frequency and of the time acquisition period. Owing to the proposed procedure, the spectrum lines related to supply frequency or to rotor-slotting frequency for an induction machine can be detected with extreme accuracy within a wide range of sampled data conditions. Then, an accurate slip computation, or speed estimation, for sensorless control or distribution network diagnosis can be performed. Comparisons between previously existing methods and the proposed one are reported, in order to critically analyze its performances. Two different-sized induction machines were used for the experiments.     

Denoising using wavelets on electric drive applications

One common problem in drives applications is the presence of noise that corrupts the useful information in measurements such as of current, due to sensor imperfections. Digital low pass filters are a solution to the problem but they cannot cope when the useful information has time varying high frequency characteristics. In this paper, wavelet analysis, seldom used as yet in electric drives, is analysed and compared to classical methods. The key points of wavelet analysis are presented in a way that is appropriate for drives. Application of this new method to a typical practical current signal demonstrates the advantages and limitations of these methods over more conventional techniques. The true power of the wavelet transform is revealed when it is applied to a speed estimation problem where the rotor speed of a permanent magnet machine is modulated and coupled with high frequency components.     

Diagnosis of Broken-Bar Fault in Induction Machines Using Discrete Wavelet Transform Without Slip Estimation

The aim of this paper is to present a wavelet-based method for broken-bar detection in squirrel-cage induction machines. The frequency-domain methods, which are commonly used, need speed information or accurate slip estimation for frequency-component localization in any spectrum. Nevertheless, the fault frequency bandwidth can be well defined for any squirrel-cage induction machine due to numerous previous investigations. The proposed approach consists in the energy evaluation of a known bandwidth with time-scale analysis using the discrete wavelet transform. This new technique has been applied to the stator-current space-vector magnitude and the instantaneous magnitude of the stator-current signal for different broken-bar fault severities and load levels.     

Optimal flux weakening in surface PM machines using fractional-slot concentrated windings

A design approach is presented for achieving optimal flux-weakening operation in surface permanent-magnet (SPM) synchronous machines by properly designing the machine's stator windings using concentrated, fractional-slot stator windings. This technique makes it possible to significantly increase the machine inductance in order to achieve the critical condition for providing wide speed ranges of constant-power operation. The conditions for optimal flux weakening can be achieved while simultaneously delivering sinusoidal line-to-line back-electromotive-force waveforms and low cogging torque. A closed-form analytical model is described that can be used to design SPM machines to achieve optimal flux-weakening conditions. This technique is applied to design a 6-kW SPM machine that achieves constant-power operation over a wide speed range. Performance characteristics of this machine are compared using both closed-form and finite-element analysis.     

Evaluation of losses in DC machines-a statistical approach

The power ratings of the drive systems used in cyclic duty applications such as flying-die and cut-to-length shears are dictated by the thermal considerations associated with the losses produced by the machine during an operation cycle and the specified production rate. Since speed and torque are both transient functions with no steady-state operating point for such systems, a study was conducted to determine an expression that would describe these losses for a DC machine as a function of its operating speed and torque. A multiple regression technique was applied to the data collected from a set of sample machines for this purpose. Starting with the analysis of individual expressions for each of the components of losses in a DC machine, two regression models are presented. The first, based on a sample size of ten machines, provides an expression for the determination of operating point losses at any specified speed and torque per unit of rated machine losses (at rated speed and torque). The second model, based on data on 64 machines, provides an expression for the determination of rated losses in percent of machine power rating as a function of rated motor speed in r/min, armature volume in cubic units (DSQL), and percent armature droop. Mean estimates are also presented for the determination of percent droop and armature volume for a range of power ratings from 50 hp to 800 hp machines     

实现感应电机宽范围最大转矩控制的电流优化策略

针对广泛应用于数控机床主轴驱动系统中的交流感应电机,提出了一种新的宽范围运行的电流优化控制策略。根据感应电机在不同速段的转矩特性,充分考虑逆变器的输出电压限制、电机本体的电流约束条件及最大转差频率限制,以输出最大转矩为目标,得出了全速范围内的最优电流控制轨迹和感应电机宽范围转矩输出最大化的电流优化分配指导原则。在此基础上,设计了一种工程实现算法,依据电机实际运行的状态变量实现恒转矩区、恒功率区与恒电压区的快速平滑过渡,完成了对最优电流控制轨迹的逼近。实验结果证明了提出方法的有效性,可以实现感应电机宽范围运行的最大转矩输出,并且使系统具有较快的动态响应性能。     

Synchronous drive performance of brushless doubly-fed motors

This paper presents studies of the steady-state performance of the brushless doubly-fed machine for adjustable-speed drive applications. The equivalent circuit and basic performance equations are presented followed by a proven technique for the solution of the least restrained form of the equations. Model predictions and experimental results are given. The studies show that the machine acts like both a synchronous motor, with power factor adjustable by control winding excitation, and a slip-ring induction machine with slip power recovery and a low converter rating. The model is suitable for development of control schemes and performance index optimization     

INDUCTION MOTOR DRIVE STABILIZATION WITH STATOR CURRENT FEEDBACK

ABSTRACT

The use of state feedback to control Induction motor drive systems is examined. Using the machine currents and speed as the system states, a general linearized formulation of the problem is derived. This formulation has the advantages of previous forms based on complex variable analysis, but is not subject to the limitations of that method.

The proposed model Is used to study machine control with stator current feedback. The results show that stator current feedback can be used to improve the dynamic characteristics of the drive system. Comparisons of stator current control with the uncontrolled machine and with the slip controlled machine are presented over the range of operating speed, load, and inertia. In all cases, advantages of current controlled operation can be seen.     

Modern improvement techniques ofdirect torque control for inductionmotor drives - a review

Conventional direct torque control (DTC) is one of the excellent control strategies available to control the torque of the induction machine (IM). However, the low switching frequency of the DTC causes high ripples in the flux and torque that leads to an acoustic noise which degrades the control performances, especially at low speeds. Many direct torque control techniques were appeared to remedy these problems by focusing specifically on the torque and flux. In this paper, a state of the art review of various modern techniques for improving the performance of DTC control is presented. The objective is to make a critical analysis of these methods in terms of ripples reduction, tracking speed, switching loss, algorithm complexity and parameter sensitivity. Further, it is envisaged that the information presented in this review paper will be a valuable gathering of information for academic and industrial researchers.     

Some Electronic Techniques for Speed and Slip Measurement in Power Laboratories

Circuits that provide a transient and steady-state measure of slip and speed for rotating machines are described. A basic stroboscope consisting of very few components, all solid state, is also described and this can be used for the measurement, under steady conditions, of synchronous machine load-angle, of speed, and also, to a limited extent, of slip. The circuit designs are modular in character and where possible integrated circuits have been used, so that students may reasonably be able to understand not only the principle of the equipment but also, when educationally desirable, something of the circuitry as well. A further objective in developing these measuring devices has been simplicity of construction and economy of components so that multiple facilities can be provided for power teaching laboratories at a minimal cost.     

永磁同步电机无位置传感器控制系统

针对传统永磁同步电机无位置传感器控制系统在低速段不能正常实施的问题,提出了一种简单但有效的永磁同步电机无位置传感器控制方法.通过在电机定子绕组中注入高频电压,利用电机的凸极效应,及对电机绕组端电流的处理计算,准确地计算出电机的转子位置和转速,实现无位置传感器控制.为了解决永磁同步电机的启动问题,提出了在电机静止状态下检测转子初始位置的新方法.仿真结果显示了所用方法的有效性和可行性.     

A Microcomputer-Based Optimal Control System to Reduce the Effects of the Parametric Variations and Speed Measurement Errors in Induction Motor Drives

A control methodology is presented for induction motor drives which makes it possible to reduce effectively the dependence of the stator flux and current both on the motor parametric variations and on the error on the motor angular speed measurement. To this aim, also the determination of the slip has been inserted in the closed-loop control system, and an optimization technique proper to bilinear systems has been applied. Then, a possible structure of the microcomputer-based controller is described, and the obtainable performances are examined by digital simulation.     

Selection criteria of induction machines for speed-sensorless drive applications

Induction motors, both three and single phase, are used extensively for adjustable-speed drives' applications. These machines are structurally very robust and are a primary source of motive power and speed control where DC machines cannot be used. For closed-loop control of these machines, sensorless speed estimation is usually preferred. Among the current estimation techniques available for speed-sensorless induction motor drives, speed measurement based on rotor-slot-related harmonic detection in machine line current happens to be a prominent one. While these harmonics can be strong in certain kinds of machines, some other machines may exhibit very weak rotor slot harmonics that can be obscured by noise. Skewing, slot shapes and types, structural unbalances, etc., also have a prominent effect on the detectability of these harmonics. This paper attempts to investigate this problem based on the interaction of pole pairs, number of rotor bars, and stator winding. Although the analysis and experimental results have been mainly provided for three-phase squirrel-cage induction motors, single-phase and slip-ring induction motors have also been addressed. Further, it has been shown that eccentricity-related fault detection could also be easily accommodated with this kind of speed detection technique at no or negligible extra cost when certain motors are selected.     

A Current-Source Inverter in the Secondary Circuit of a Wound Rotor Induction Motor Provides Sub- and Supersynchronous Operation

A control system is described in which a current-source inverter is connected between the secondary winding of a three-phase slip-ring induction motor and the ac mains supply to give a variable speed sub- and supersynchronous operation. Control techniques developed in an earlier work were used to ensure fully stable operation over a very wide speed range with either driving or braking torque. Means are provided for power-factor control to compensate for the lagging power-factor effect of the inverter when operating into the large secondary electromotive forces (EMF) at high slip values. Experimental results are presented for a speed range from standstill to approaching twice synchronous speed for both driving and braking torque. There are no instabilities and the developed torque even at low frequencies near synchronous speed is steady with motor derating due only to the quasi-square wave current in the secondary circuit.     

Transient Performance of Permanent Magnet AC Motor Drives

The transient behavior of permanent magnet ac motor drives is analyzed. A new model is proposed where particular emphasis is placed on the role that armature reaction and saturation effect play on the flux distribution of the machine. Equations for calculation of these fluxes are deduced and verified by experimental tests on the machine. Simulation of motor transients both for constant and variable speed operations are presented and compared with experimental tests.     

Sensorless vector controller for a synchronous reluctance motor

A new high-performance sensorless speed vector controller that implements the maximum torque per ampere control strategy for the inverter-driven synchronous reluctance machine is presented in this paper. It is based on a parameter-dependent technique for online estimation of rotor position and angular velocity at the control rate. The current ripple principle is used to estimate position. The estimates are fed to a conventional closed-loop observer to predict the new position and angular velocity. The very high accuracy of the sensorless control algorithm at both low and high speeds is confirmed by experimental results