T-connected autotransformer-based 24-pulse AC-DC converter for variable frequency induction motor drives

A new robust passive waveshaper based on 24-pulse ac-dc conversion is proposed to feed voltage source inverter (VSI) supplying squirrel-cage induction motor drive. The passive waveshaper consists of a newly designed T-connected autotransformer with less number of windings resulting in simplicity in design and manufacturing. The proposed 24-pulse ac-dc converter is found capable of suppressing less than 23rd harmonics in the supply current. The power factor is also improved to near unity in the wide operating range of the vector-controlled induction motor drive (VCIMD). Finally, the design of the autotransformer is modified to make it suitable for applications, where presently a 6-pulse diode bridge rectifier is used. A laboratory prototype of proposed T-connected autotransformer-based 24-pulse ac-dc converter is developed and test results are presented to validate the developed design procedure and the simulation models of this ac-dc converter under varying loads.     

A comparison of induction motor models for bus transfer studies

A study was undertaken to determine if improved accuracy can be obtained using different induction motor models for bus transfer simulations where the loads have low inertias. Bus transfer simulations are presented using five different models. Based on a comparison of these simulations, separate motor models for the disconnect period, the period immediately after reenergization, and the longer time period during which bus voltage and motor speeds are restored are recommended     

Identification of induction motor equivalent circuit parametersusing the single-phase test

In this paper, a new method of identification of the induction motor equivalent circuit parameters is introduced and discussed. The proposed method uses single-phase test results as a base test for calculating the equivalent circuit parameters of the induction motor. The single-phase test is performed using a variable frequency power supply (inverter). The test was conducted at various frequencies while the voltage, current and power factor were measured. Thereafter, the motor parameters are calculated. The precision of calculation of the motor parameters is sensitive to the accuracy of measurements which can be improved by the use of high performance microprocessors     

Estimation of induction motor double-cage model parameters from manufacturer data

This paper presents a numerical method for the estimation of induction motor double-cage model parameters from standard manufacturer data: full load mechanical power (rated power), full load reactive electrical power, breakdown torque, and starting current and torque. A model sensitivity analysis for the various electrical parameters shows that stator resistance is the least significant parameter. The nonlinear equations to be solved for the parameters determination are formulated as a minimization problem with restrictions. The method has been tested with 223 motors from different manufacturers, with an average value of the normalized residual error of 1.39/spl middot/10/sup -2/. The estimated parameters of these motors are graphically represented as a function of the rated power.     

Improvement of induction motor drive systems supplied byphotovoltaic arrays with frequency control

The overall efficiency of an induction motor drive system, powered by a PV array, drops significantly when the insolation condition varies away from its nominal level. This problem can be overcame using a control method in which the frequency of the inverter's PWM control signal is adjusted according to the insolation and temperature conditions. The motor speed, and therefore, the power delivered to the load, are adjusted by controlling the inverter's frequency. This eliminates the mismatch between the maximum power that is available from the source and the power that is required by the load. Simulation results presented in this paper show that using the proposed control system allows the induction motor drive system to maintain its optimum efficiency and deliver consistently more power to the load when insolation and temperature vary from the nominal level. This method also offers an improvement in the system stability     

适合于变速恒频双馈感应发电机的Crowbar对比分析

电网运行新规则要求变速恒频双馈感应发电机在电网电压跌落的情况下仍与电网相连接，为做到这一点需要安装低压旁路系统。综合分析了低压带来的负面影响以及低压旁路的具体实现方法；对比了多种Crowbar电路各自的优缺点；最后介绍了变速恒频双馈发电机相关保护控制策略和新型旁路系统。     

Identification of high-order synchronous generator models from SSFRtest data

This paper presents a direct maximum-likelihood estimation procedure to identify the synchronous machine models based on the standstill frequency response (SSFR) test data. The method presented in this study is the first and only algorithm utilizing all available SSFR test data under both shorted and open field circuit conditions to establish a unique equivalent circuit model by maximizing the conditional probability density function of the error residuals. The method is applied to the modeling of two well-known generators, namely the Rockport and Nanticoke generators, using the measured SSFR test data. The results of the study show that by incorporating both the open and short-circuit SSFR data in the modeling process, the SSFR characteristics of the two generators can be accurately represented by the established high order synchronous models up to 1 kHz. The identified synchronous machine model consists of five amortisseur windings on each axis. In addition, an eddy-current effect impedance is included in the d-axis model for representing the increased influence of rotor eddy current under the open-circuit test condition     

Noiseless variable-speed squirrel-cage induction motor

A variable-speed squirrel-cage induction motor is proposed. It is made up of a squirrel-cage rotor and two stators, one of which can be turned for speed control. The proposed motor has the following special features: (1) The range of speed control is extremely wide and the motoring operation is almost constant-torque under constant supply source voltage and frequency. (2) No special source such as an inverter is required; (3) Smooth operation from starting to the rated speed can be expected without any special starter because of suppressed starting current and large starting torque. The results of a theoretical analysis and experiments on a test motor are given, and the characteristics of the motor are discussed     

变风速下双馈异步风机在微电网中的电压频率协调控制

微电网线路阻抗比值较大,当微电网孤岛运行时,负荷频繁投切导致微电网电压、频率波动较大。文章对双馈感应风电机组与柴油机协调控制共同为微电网提供电压、频率支撑,提出了DFIG在微电网中的电压、频率协调控制策略。DFIG有功功率控制采用虚拟惯量控制与超速减载控制,并采用f-P下垂控制与柴油机配合对微电网频率进行调节。通过控制DFIG转子侧换流器的无功功率,并采用V-Q下垂控制与柴油机配合对微电网电压进行控制。最后在DIgSILENT中搭建了风光柴中压微电网模型,仿真结果验证了文章所提控制策略的有效性。     

Helical motion tubular induction motor

The paper describes a new form of tubular induction motor, in which the motion of the rotor conductor is along a helical path. The winding arrangement described may include multi-polar system circumferentially and axially. The excitation produced by such winding is a helically travelling wave. An appropriate multi-layer analysis using cylindrical geometry is presented. Experimental and theoretical results are given and they show good correlation.     

Small induction motor noise calculation

There has been an increasing demand for a quiet induction motor. Electromagnetic noise is jarring to the ear. Most offensive electromagnetic noise is generated when the natural frequencies of the stator coincide with or are close to the frequencies of the magnetomotive forces. In this paper, electromagnetic noise is calculated by boundary element method (BEM) program using the electromagnetic forces of Maxwell stress. The natural frequency and behavior of the stator are calculated by mechanical finite element method (FEM), considering the contact between stator core and frame. Spring elements are introduced between the stator frame and the stacked core. Vibration is calculated by mechanical FEM. Calculated and experimental noise level were within 3 dB(A) at 1200 and 4080 Hz.     

Conductors of a linear induction motor

In this paper, the joint effect on the thrust and attraction forces of a linear induction motor is discussed and a control algorithm to compensate for such effects is presented. The algorithm is based on the vector control technique and takes into account the variation of the secondary resistance of the LIM when a joint enters the active zone of the LIM. The algorithm was tested by simulation on a sample of linear motor elevator system. Simulations have shown that the fluctuations of the thrust and attraction forces where decreased significantly     

开关磁阻调速电动机运行实例分析

对开关磁阻电动机调速系统的组成、工作原理、使用情况和节能效果进行了总结分析。     

分布式变频水泵的节能分析

简述分布式变频水泵的节能原理,以热水系统为例,对动力集中式供热系统和分布式变频供热系统进行定量分析,计算结果表明:设计工况下传统供热方式阀门能耗占总能耗近30%,分布式变频系统阀门能耗几乎为0,同时水泵的能耗也大大降低,而两种供热方式的初投资相差无几。分布式变频系统代替电动调节阀具有很大的节能潜力。     

分布式变频泵供热系统综述

分布式变频泵供热系统可以降低建筑能耗,对该系统有大量的研究,对分布式变频泵供热系统进行介绍,其次在研究现状和应用现状方面进行论述,最后指出系统中存在的问题。     

Magneto-thermal coupled analysis of canned induction motor

The authors present the calculation of the distribution of the transient temperature in the rotor bars of a canned induction motor, during locked rotor conditions, where the phenomena of electromagnetically induced currents and heat transfer are coupled. They have developed a coupled finite element electromagnetic code called WEMAP in which the calculated power loss densities are used as the heat sources for a transient thermal solution in subregions of the original problem geometry. These subregions are enclosed by surfaces on which either temperature or a convection boundary condition is known. In addition, the change in rotor bar resistance as a function of the temperature is included in these calculations. The calculated temperatures are compared with test results, and favorable agreement is obtained     

A new approach to direct torque control of induction motor drivesfor constant inverter switching frequency and torque ripple reduction

In this paper, a new approach to the direct torque control (DTC) of induction motor drives is presented. In comparison with the conventional DTC methods, the inverter switching frequency is constant and is dramatically increased, requiring neither any increase of the sampling frequency, nor any high frequency dither signal. The well-developed space vector modulation technique is applied to inverter control in the proposed DTC-based induction motor drive system, thereby dramatically reducing the torque ripple and speed ripple. As compared to the existing DTC approach with constant inverter switching frequency, the presented new approach does not invoke any concept of deadbeat control, thereby dramatically reducing the computations. Experimental results are illustrated in this paper confirming that the proposed DTC method has the above-mentioned features even at the low speed range down to ±1 r/min     

An efficiency-optimization controller for induction motor drives

When working close to their nominal operating point, induction motors are high-efficiency machines. However, at low load, efficiency is greatly reduced when magnetization flux is maintained at nominal value. Therefore, it is necessary to adjust the flux level according to the load, so as to decrease iron and copper losses. This paper deals with a field-oriented scheme for induction motor drives leading to efficiency optimization. It is based on optimal power factor tracking by adjusting magnetization current component with to respect the torque current component. Simulation results are presented to highlight the feasibility and validity of the proposed method     

A capacitor start three phase induction motor

A scheme for the fast starting of three-phase induction motors is proposed. This scheme is based on starting the motor from a single-phase power supply with the help of a phase balancer properly selected for achieving maximum starting torque. As the speed reaches a predetermined value, a simple centrifugal switch is used to reconnect the motor to the three-phase supply. The feasibility of the proposed scheme is proven through the development of a rigorous state-space mathematical model and its associated digital simulation, followed by experimental verification