REACTIVE POWER COMPENSATION OF A THREE-PHASE TANDEM INDUCTION GENERATOR

ABSTRACT

This paper examines the ability of capacitors connected in the supply lines to one stator to improve the power factor and efficiency of a two stator (one moveable), single squirrel-cage, three phase induction machine termed a tandem machine. An equivalent circuit model incorporating the series capacitor is presented. Theoretical modeling for a typical set of equivalent circuit parameters and optimum capacitance show the tandem induction generator's power factor transformed from lagging to leading and the efficiency improved by one to three percentage points. Results from laboratory tests on a one horse power tandem motor for two different values of capacitance are included.     

TRANSIENT AND STEADY-STATE ANALYSIS OF A VOLTAGE CONTROLLED INDUCTION MOTOR DRIVE WITH DELTA CONNECTED WINDINGS

ABSTRACT

This paper deals with the transient and steady-state analysis of a voltage controlled induction motor (VCIM) drive with delta connected windings. Symmetrically triggered back-to-back connected thyristor pairs are used in each of the three lines to effect change in terminal voltage. Using a three-phase stator side equivalent circuit of the induction motor, the state equations for different modes of operation are formed and solved using a digital computer. The results of the transient and steady-state analysis for a specified triggering angle and load torque are presented and compared with those for a wye connected motor.     

POWER CONTROLLER FOR A WIND-TURBINE-DRIVEN TANDEM INDUCTION GENERATOR

ABSTRACT

A controller for delivering either constant power or maximum power from a wind-turbine-driven grid connected induction generator with double stator windings, one fixed and the other able to be physically rotated, and a squirrel-cage rotor common to both stators is described. The load torque of the generator is controlled by varying the angular displacement between the two stators. The generator can feed power to the grid at variable speed and constant frequency and is termed a Tandem Induction Generator.

Dynamic models for the wind energy conversion system are proposed for both controlled and uncontrolled operation to predict changes in shaft speed to shifts in wind speed using data pertaining to a commercial wind turbine. Results based on laboratory tests on a 1hp tandem machine driven by a dc motor demonstrating the feasibility of both controllers are presented. A steady state model of the tandem generator is also proposed and compared to measurements made on the test machine.     

Evaluating the Parameters of the Equivalent Circuit of Single-Phase Induction Motors

ABSTRACT

An algorithm is proposed in this paper which evaluates the equivalent-circuit parameters of single-phase induction motors. Two parameters are kept constant at all speeds: the resistance of the stator winding, and the resistance representing the core losses of the motor. All other parameters must vary with the speed of the motor, so that the equivalent circuit is able to match exactly the performance of the actual motor. The parameters are evaluated from standard test data taken at standstill, at no-load, and under load conditions.     

A MODIFIED EQUIVALENT CIRCUIT FOR THREE-PHASE INDUCTION MOTORS WITH BALANCED NONSINUSOIDAL VOLTAGE SOURCE

Abstract

In this paper, the equivalent circuit model of a three-phase induction motor with balanced nonsinusoidal voltage waveform is solved by the experimental test of a 3-phase, 3-hp induction motor with a variable voltage, variable frequency (VVVF) voltage source. The parameters are calculated by analyzing the test results with statistical methods.

The performance of an induction motor with nonsinusoidal voltage source is calculated by the computer simulation based on the circuit model derived. The simulation results are compared with the laboratory test to verify the accuracy of the equivalent circuit model.     

DETERMINATION OF IRON LOSS DISTRIBUTION IN INVERTER FED INDUCTION MOTORS

ABSTRACT

An approach based on the temperature-time method was used to investigate the iron loss density distribution in a 4 kW, 415V, 3-phase, 4-pole induction motor under both sinusoidal and inverter fed conditions. A test rig was constructed to allow loss densities to be evaluated at discrete points within the machine. A model based on interpolate functions was constructed to give the full loss density distribution throughout the stator iron. It is shown that iron losses increase considerably towards the ends of the stator core stack, particularly for the inverter fed case. The results are verified with those obtained from established models based on an equivalent circuit representations.     

SINGLE-PHASE INDUCTION MOTOR WITH ASYMMETRICAL STATOR

ABSTRACT

This paper describes a single-phase single-winding induction motor which is self-starting without the use of a shading winding. Starting torque is produced by a combination of several stator asymmetries: an airgap under the main pole which is-tapered down in the direction of rotation, poles without windings in the quadrature axis with solid iron flux bridges to the lagging sides of the main poles, and yoke sections which are larger on the leading than on the lagging sides of the main poles. A qualitative explanation of the action of these asymmetries is presented using equivalent circuits.     

PERFORMANCE ANALYSIS OF LOAD COMMUTATED INVERTER FED CAGE INDUCTION MOTOR DRIVE

ABSTRACT

An approach, to analyse the performance of a variable speed cage induction motor drive fed from load commutated inverter (LCI), is presented. Induction motor with an appropriate capacitor across its stator terminals constitutes the load on the inverter. A fully controlled bridge converter, supplied by a variable dc voltage source, commutated with the back emf of the motor, acts as an inverter. An algorithm to compute the motor performance, is developed using equivalent circuit representation of the system. Strategies for the selection of control variables, in order to achieve the desired speed range for satisfactory performance of the drive are given. The performance of a 3-hp, cage induction motor fed from LCI is computed, using the developed algorithm for wide range of speed; and is verfied experimentally.     

HARMONIC ANALYSIS OF INDUCTION MOTORS WITH STATOR FAULTS

ABSTRACT

In the paper stator faults are analyzed by means of a procedure based on the space-vector theory. The used approach, due to Stepina, allows to consider separately each conductor of every single slot and therefore to take easily into account the winding dissymmetry.

The interactions among the different harmonic fields are studied by starting from the topological structure of windings and the harmonic analysis of the currents and of torque Is carried out.

The method is tested to numerical computations of steady-state currents for an induction machine with different positions of stator short-circuits.

Finally the procedure is validated by using an experimental squirrel cage machine, having stator windings constructed so as to realize different short-circuits.     

五相感应电动机定子绕组匝间短路仿真分析

建立了五相集中整距绕组感应电动机定子绕组匝间短路时的统一模型.通过该模型,可以分析定子各种短路故障及各电机参数对定子绕组匝间短路的影响.针对电机一相出现匝间短路时的情形,利用Matlab/Simulink 进行了仿真计算,通过对比Ansoft场路耦合计算结果,可以发现,两种结果是相吻合的,在一定程度上验证了所建立模型的...     

双定子实心转子盘式异步飞轮电机新型等效电路模型分析

双定子实心转子盘式异步飞轮电机具有可高速运行、可靠性高、结构简单、成本低等优点,可作为低成本的飞轮储能系统中电动/发电机用.该电机的等效电路模型与参数对于性能分析、推导控制策略至关重要.针对该电机的结构特点,根据实心转子内磁场分布规律,采用分环分层法以及表面阻抗理论推导了一种新型等效电路模型,该新型等效电路模型相比于传...     

Diagnosis of Short‐Circuit Faults in Stator Winding Inside Low‐Voltage Induction Motor Using Impulse Voltage Test

Short‐circuit faults in windings due to the deterioration of insulation is among the most common faults in motor drive systems. An easy and effective fault diagnosis method is urgently required to ensure highly reliable operation. This paper proposes a novel method for the diagnosis of short‐circuit faults in stator winding inside a low‐voltage induction motor without removing the rotor, by performing an impulse voltage test. As the rotor does not need to be removed from the motor in this novel diagnosis method, the method can be put to practical use. In this study, first, several impulse voltage tests are carried out on the stator windings of motors. Second, the values of two features that represent the characteristics corresponding to the condition of the motor are calculated, and it is found that the shape of the feature distribution does not depend on the rotor position but on the condition of the winding. Third, the distance between the feature distribution for the healthy motor and features obtained from a target motor is calculated. On the basis of this distance, the condition of the stator winding inside the induction motor is determined. The effectiveness of the proposed diagnosis method is verified by performing experiments that involve several motors with healthy and faulty windings.     

基于回路电流法的双抽头单相电机的网络方程

借助于异步电机的等值电路,采用了与传统的交轴磁场法和旋转磁场法不同的分析方法。该方法通用性强,适于分析定子绕组具有各种不同连接方式的异步电机的稳态运行性能,并能列写出便于计算机辅助计算矩阵方程。以定子绕组连接复杂的双抽头单相电机为例,该方法把该电机的定子电路分成了2个回路和6条支路,选择其中的1条支路作为基准支路,转子绕组向基准支路中的绕组折算,各支路绕组中的正序与逆序感应电势当作流控电压源进行处理,然后由回路电流法列写出了计算电机性能的网络方程,为验证计算结果,给出了1台双抽头单相电扇电机某些电流与电压的计算值,并与实测值作了比较,计算值与实测值的相互吻合说明了网络方程的正确性。     

直接转矩控制的无刷双馈感应电机的异步启动

针对无刷双馈感应电机( BDFIM)异步启动电流及启动转矩的解析分析不足的问题,利用等效电路推导出BDFIM异步启动阶段两个定子绕组的电流和启动转矩的解析表达式.分析结果表明,功率绕组的启动电流小于同容量的感应电机.针对BDFIM直接转矩控制系统牵入同步时电流大的问题,提出了磁链优先的方法,即在牵入同步的过程中,根据控制绕组磁链所在的扇区,选择合适的电压矢量,优先建立磁链,待磁链增加到设定的阈值时,再兼顾磁链和转矩.样机的实验结果表明,磁链优先的控制方法能够有效减小两个定子绕组的牵入电流.     

三绕组串联式高效单相感应电动机瞬态性能

三绕组串联式高效单相感应电动机三个定子绕组串联连接,并与两个电容器连接,可以实现在单相电源下接近对称运行.与同容量普通单相感应电动机相比,具有体积小、效率高的特点.本文从对称分量法和该电机的定子绕组电路结构出发,推导了电机对称运行条件,建立了a-b-c坐标系下的瞬态数学模型.利用该仿真模型分析了电机的动态性能,研究了电...     

PERFORMANCE OF ROTARY-LINEAR INDUCTION MOTOR WITH ROTATING-TRAVELING FIELD

Abstract

A rotary-linear induction motor whose stator creates a magnetic field traveling helically is presented. A theory of such a motor is derived taking into account a finite excitation length of the stator. Results obtained from the calculations are verified experimentally.     

Scalar control systems for a traction induction motor

A brief review and comparative characteristics of scalar control systems for traction induction motors for using in the traction electric drive are presented. It is shown that, despite the obvious advantages of the systems of vector control and direct torque control, scalar control systems have found wide application. The operation features of scalar control systems with stability0 of absolute slip and a minimum of stator current are considered. Based on the equivalent circuit of an induction motor taking into account the stator and rotor iron loss, a comparative evaluation of the considered scalar control systems based on the criterion of the efficiency coefficient taking into account the temperature of the stator and rotor windings is presented. Simulation results in the MATLAB environment for an 11-kW induction motor are presented. It is established that scalar control systems operating under the principle of a stator current minimum have an advantage, as this maintains the desired torque value with higher values of efficiency coefficient, which decreases electromagnetic loads and power loss. It is shown that it is necessary to take into account the influence of windings temperature on the stator voltage and the parameters of the control system in connection with its affect on the minimum stator current and optimal absolute slip ensuring extremal control by current minimum.     

Approaches to suppressing shaft voltage in brushless DC motor driven by PWM inverter

This paper describes the approaches to suppressing the shaft voltage and bearing current by electrostatically shielding the stator end windings of the brushless DC motor driven by PWM inverter. At first, measured shaft voltage and bearing current are compared with those calculated waveforms to verify the common mode equivalent circuit of the brushless DC motor. Next, the relationship between shaft voltage and stator winding to rotor capacitance is calculated using the common mode equivalent circuit. Finally, the electrostatic shielding of the stator end windings is evaluated to reduce the shaft voltage by experiments and calculations. ©2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 73–79, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20701     

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.     

SPLIT-WINDING STARTING OF A SINGLE-PHASE INDUCTION MOTOR

Abstract

Results of investigation of starting a single-phase induction motor having a single stator winding and using normal stator and rotor punchings are presented in this paper. Theoretical and experimental studies show that the motor requires less copper for its stator winding compared to a split-phase motor and the overall starting performance is very satisfactory.