Variable-structure torque control of induction motors using space vector modulation

Compared with field orient control (FOC), direct torque control (DTC) is known to provide fast and robust response for induction motors. However, while offering high dynamic performance, classical DTC produces notable torque, flux, and current ripples, and operates with a variable inverter switching frequency. In this paper, a novel torque control scheme for induction motors is proposed. The stator flux and the electrical torque are directly controlled by variable-structure controllers, and stator voltage vectors calculated by the variable-structure controllers are applied to the motor by means of space vector modulation. The proposed scheme therefore provides smooth, fast and robust regulations of the electrical torque and the stator flux. Moreover, the implementation of the scheme is simple. Theoretical analysis shows the asymptotical convergence of electrical torque and stator flux tracking. Simulation and experimental results are provided to evaluate the performance of the proposed scheme.     

EMTDC异步电动机模型及起动过程仿真

详细介绍了EMTDC中三相异步电动机模型,尤其是机械部分模型,给出了机械部分与电气部分的接口以及暂态求解过程.基于EMTDC对正常情况、定子匝间短路及转子断条故障时的起动转速-转矩关系进行了仿真研究,得出了仿真曲线,分析结果证明利用EMTDC可为内部故障诊断提供一个仿真环境.     

STS and induction motors

Industrial plants with a high amount of induction motor load can run into problems following short interruptions of the supply or voltage sags. After the voltage has recovered, the high current drawn by the motors can cause voltage collapse. The case study presented in this article shows that the static transfer switch (STS) can provide a solution to this problem by transferring the loads to an alternative healthy supply within some milliseconds from the occurrence of the disturbance. However, this case study has also shown that the time needed for transferring the load is dependent on the type of disturbance and the instant when it occurs, and the transfer time is, in general, higher with an induction motor load, as compared with static load. For plants with a high percentage of motor load, a specific performance study should be carried out to assess if the installation of the STS actually improves the power quality for the plant.     

Prediction of acoustic noise from variable-speed induction motors: deterministic versus statistical approaches

The traditional approach for the prediction of noise radiated from induction motors is usually based on a deterministic approach in which the motor is modeled using finite-element and/or boundary-element methods (FEM/BEM). A great deal of structural details has to be modeled using the deterministic approach. While these deterministic methods have been shown to provide reasonable estimates of the radiated acoustic noise at low frequencies (usually, well below 2 kHz) and for small motors, the demands on computing memory and time render calculations at high frequencies and for large motors almost impossible to make. In this paper, a statistical method especially suited for calculations at high frequencies is introduced. The statistical approach does not require the same amount of details to be modeled as in the FEM/BEM because only the averaged noise within a given frequency band is sought. Furthermore, it utilizes the analytical results obtained from simple structural elements that make up the motor structure. Results demonstrate the feasibility of the method, its ability to discern the contribution of various components of a motor to the overall radiated noise, and substantial savings in the computational effort compared with FEM/BEM.     

Correlation between winding geometry and parameters and overvoltage in induction motors operating from power-width modulation converters

The influence of the number of winding parallel branches, steel sheets thickness in the magnetic system and the size of air gap on the overvoltage in the induction motor operating from power-width modulation converters is investigated. The mathematical model and the results of simulation of the wave processes that take place in the multiturn mush winding of a squirrel-cage motor are presented.     

Harmonic modeling of induction motors

The paper proposes an induction motor model for the study of harmonic load flow in balanced and unbalanced conditions. The parameters of this model are obtained from motor manufacturer data and the positive- and negative-sequence equivalent circuits of the single- and double-cage models. An approximate harmonic model based on motor manufacturer data only is also proposed. In addition, the paper includes manufacturer data and the calculated parameters of 36 induction motors of different rated powers. This database is used to analyze the proposed models.     

Determination of parameters in interior permanent-magnetsynchronous motors with iron losses without torque measurement

This paper proposes systematic procedures to estimate the circuit parameters of an inverter-fed vector-controlled interior permanent-magnet synchronous motor when torque measurement is not available. The methodology presented here does not neglect iron losses. New procedures have been developed and justified since international standard recommendations (International Electrotechnical Committee Standards) cannot be applied. Experimental results from a test rig are presented in this paper to validate the most important contributions. Thanks to the procedures proposed, secondary effects on the motor parameters, e.g., saturation or frequency dependency, have been evaluated     

Two-dimensional spatial-phase simulation of electromagnetic processes in induction motors with the goal of obtaining mechanical characteristics

The spatial-phase method of mathematically simulating electromechanical energy transformations in electrical machines of rotating motion is examined. Methods of taking into account the dynamic magnetic properties of a magnetic conductor that consists of a plate package and a method of calculating the electromagnetic moment of a machine using the calculated distribution of field vectors are presented. Brief results of computational experiments with a two-dimensional spatial-phase model of an induction machine are described.     

Causes and effects of single-phasing induction motors

It is well known that a three-phase induction motor will continue to operate when a disturbance of some sort causes the voltages supplied to the motor to become single phased. Single phasing can occur as a result of a fuse blowing or a protective device opening on one phase of the motor. Other possibilities include feeder or step-down transformer fuses blowing. Even though the motor will continue to operate in this condition, the motor will heat up very quickly, and it is essential that the motor be removed from service by the opening of a motor circuit breaker or some other type of protective device. This paper will describe three different ways in which an induction motor will operate in a single-phase condition. For purposes of this paper, "single phase" will include any condition in which the three line-to-line voltage phasors appear on the same line.     

Proper specification and installation of induction motors

To achieve years of trouble-free operation, the proper motor for an application must be chosen. This requires that the motor be properly specified for the specific application, taking into account any special ambient conditions, performance requirements or environmental concerns. Without this, nothing else will matter. This article discusses how to determine the minimum acceptable motor for an application. It also makes recommendations for selecting additional features yielding higher protection and performance, and gives tips regarding installation and maintenance     

Capacitor braking of double-cage induction motors

Capacitor braking relies on the self-excitation process and represents a well-established technique of braking of single-cage induction machines. However, there appear to be no papers on the capacitor braking of double-cage induction motors. Since the self-excitation process constitutes the basis of capacitor braking, a correct representation must include the effects of main flux saturation in the induction machine model used. The paper first summarises the mathematical model of a saturated double-cage induction machine and then presents experimental results together with results of a comprehensive simulation study. Both symmetrical three-phase and asymmetrical single-phase capacitor braking techniques are considered. The results are shown for two different double-cage induction machines. The experimental and simulation results are found to be in good agreement.     

Online condition monitoring of induction motors

Condition monitoring of induction motors is a process that may be used to great advantage in mining and other industrial applications. The early detection of motor winding deterioration prior to a complete failure provides an opportunity for maintenance to be performed on a scheduled routine without the loss of production time. Presented in this paper is a theoretical and experimental analysis of a voltage mismatch technique that may be used in operating situations to monitor the health of induction motor windings. It extends previous work in this area by demonstrating the robust nature of the monitoring process not only under conditions of power supply unbalance but also in situations where motor construction imperfections exist and mechanical loads are unpredictable. A suggested procedure for application of this condition monitoring process in industrial situations is also included.     

Condition monitoring of slip-ring induction motors

A technique for real-time condition monitoring of slip-ring induction motors is presented. The proposed method utilizes on-line sensing and analysis of the rotor current to assess the integrity of the motor. The theoretical basis for this approach is presented; the results of an experimental investigation are given. The paper is concluded with a discussion of the efficacy of the proposed method in industrial power systems.     

异步电机弱磁区转矩最大化策略

异步电机工作在弱磁区时,转矩随着转速的升高急剧下降,在转子磁场定向系统中,充分利用电机和逆变器的最大电压、电流限制,无需d轴电流控制器,通过调节q轴分量,稳定高速失步状态,实现弱磁区转矩最大化。异步电机在电压极限状态遇到干扰时,通过旋转定子电压矢量产生动态电压边缘,提高系统的瞬态响应。当异步电机运行在弱磁区,铁损增大,影响电机的磁链水平和转矩输出,引入铁损补偿机制,确保弱磁区的转矩最大化。仿真和实验证明,该控制系统能实现异步电机弱磁区转矩最大化,且具有很强的鲁棒性。