ANALYSIS OF A SERIES-DELTA CONNECTED TANDEM INDUCTION MOTOR

Abstract

A tandem induction motor comprised of two independently housed stator windings, one housing stationary and the other able to be physically rotated, and a squirrel-cage rotor common to both stators is described. When the motor is fed from a single source, altering the position of the moveable stator changes shaft speed in a similar manner to operating a normal induction motor at variable terminal voltage

This paper presents an equivalent circuit model of the tandem induction motor for series-delta connected stator windings. Using the equivalent circuit stator current, power factor, and torque are calculated and then compared to laboratory test results obtained from a 3 kW tandem motor test rig     

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.     

TRANSIENT ANALYSIS OF BRAKING MODE OPERATION OF INDUCTION MOTOR FED FROM A VARIABLE FREQUENCY SOURCE

ABSTRACT

The transient behaviour of a three phase induction motor in the braking mode is investigated when the motor is fed from a variable frequency source. Appropriate voltage and frequency conditions to ensure minimum stopping time for plugging as well as for the case when plugging is used in conjunction with regenerative braking are identified. A dynamic model has been developed using the theory of instantaneous symmetrical component and associated operational equivalent circut and therefrom the transient performance of the motor in both the cases are compared with that of the normal plugging.     

TEST PROCEDURE FOR VERY HIGH SPEED SPINDLE MOTORS

Abstract

In the last ten years, the new power electronic devices and the new control techniques have allowed to open new application fields for adjustable speed/torque electrical drives. Although the traditional dc drives keep still the market supremacy, the new ac drives have performance really attractive and some additional benefits due to the machine structure and to the maintenance costs. Usually, ac drives use induction or brushless motors and the power amplifiers are driven by variable voltage/frequency in order to obtain variable speed. The authors deal with induction motors fed by non conventional supplies at very high frequency. In order to evaluate the total motor losses and the single items, a test bench with a synchronous machine capable to work up to 2 kHz with sinusoidal output voltage has been set up. As a consequence, an induction motor equivalent circuit with parameters depending on the frequency has been proposed. Today, the empirical procedure is that to use for high frequency applications shelf motors derated of a factor 10 to 20 % in order to keep into account the extra harmonic losses. On the other hand, the authors propose to design ‘ad hoc’ the motors for six-steps continuous operation in order to get about the same efficiency of standard motors. The new proposed motor equivalent circuit together with the test procedure seem to be a practical tool in order to aid the new motor design.     

LOSS ITEMS EVALUATION IN INDUCTION MOTORS FED By SIX-STEP VSI

ABSTRACT

At present time, induction motors are widely supplied from several types of solid-state adjustable voltage-frequency controllers with a wide range of operating features. However, in any case, the motor has to be derated for the harmonic effects due to the non-sinusoidal nature of the supply voltage. The authors propose a simple method based on the no-load and short circuit test in order to get the useful machine parameters to adopt in equivalent circuit model for the losses evaluation. Complete experimental results are reported and the comparison between six-step and sinusoidal supplies are summarized.     

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.     

Comparative Study of Dynamic Mathematical Models for Deep-Bar Rotor Induction Machine

ABSTRACT

The paper is concerned with the problem of mathematical modelling of the deep-bar rotor induction machine. Two kinds of models were analysed in this paper. The multiple-rotor circuit modal with constant parameters was presented in which the rotor circuit was replaced by a finite number of R-L sections. The method of determining of section parameters for trapezoidal rotor bars on the basis of Riccati differential equation solution was demonstrated. Then the one-rotor circuit model with parameters changing in function of the motor slip was analysed. The method of the equivalent circuit parameters determining on the base of motor nominal data for any rotor bar shape rectangular or trapezoidal was presented. Proposed models were used for simulation of asynchronous motor transients. Results of the digital simulation and laboratory tests were discussed and presented mathematical models were compared.     

Computer-Aided Analysis of a Converter-Fed Saturated Synchronous Motor Drive

ABSTRACT

A method of numerical simulation for evaluation of the performances of a variable speed synchronous motor drive is developed. The machine has rotor saliency with armature and damper windings. Magnetic saturation in both d and q axes are also taken into consideration. The model is focused specially for analysis of a self-controlled reluctance motor drive fed either by voltage source inverter or current commutated inverter. The computer solution permits accurate calculation of current, voltage, and torque waveforms. Sample calculations for highly saturated converter-fed reluctance motor drive are presented including comparison with practical tests.     

BOND GRAPH SIMULATION OF A CURRENT SOURCE INVERTER DRIVEN INDUCTION MOTOR (CSI–IM) SYSTEM

ABSTRACT

Based on the bond graph approach, the paper presents a developement of a dynamic model required for the simulation of a current–source–inverter (CSI) driven induction motor. The induction machine Is represented by the mutually perpendicular α–β model in a stationary reference frame, and is linked with the three phase current source inverter by a power conserving transformation which is taken as displacement modulated transformer structure In the bond graph model. A specific digital simulation program (COSMO–CAD) yields state space representation of the system from the bond graph structure with no reference to particular circuit configurations, representing various modes, during normal or abnormal operation. The acceptability of the simulation technique is shown by comparison of some results with those obtained from an available method of simulation.     

CLOSED LOOP PERFORMANCE OF INDUCTION MOTORS WITH CONSTANT VOLTS/HERTZ CONTROL

ABSTRACT

Characteristics of a closed loop induction motor drive, supplied from a variable frequency voltage source, and operating under constant volts/hertz control are presented. The motor linearized equations in the synchronously rotating reference frame are used to analyse the drive dynamic performance. It is shown that this performance can be greatly improved by including a properly designed speed controller in the drive structure. Thus, the decrease in stability, associated with the open loop motor operation is eliminated and the resulting drive gives satisfactory performance over the entire input frequency range. The experimental results, which confirm the validity of the motor dynamic model are also included.     

DETERMINATION OF HEAT STATE OF NORMAL LOAD INDUCTION MOTORS BY A NO–LOAD TEST RUN

ABSTRACT

Determining the nominal thermal conditions of Induction Motors (IM) experimentally requires the appropriate equipment for loading the motor, expending the electrical energy and an enormous amount of time, The difficulties of these tests increase with the size of the motors and when it is necessary to perform the tests at the place of installation. This paper discusses the heating process of induction motors in a no–load test run under normal and over–voltage conditions. The method of prediction and recounting the results of a no–load test of IM on a full load run is proposed. The theoretical research of heat processes into IM is based on its thermal circuit and its electrical equivalent. Some of the parameters of the equivalent circuit were determined from the experiment. The influence of the technological uncertainties of manufacturing IM on their thermal parameters is also discussed.     

The Minimum Input Power Conditions for Induction Motors Fed from Variable Frequency Sources

ABSTRACT

A simplified analytical method, based on the equivalent circuit of an induction motor, is presented for computing the frequency and voltage corresponding to the minimum input power. This optimum operating condition is determined for a specified torque and within a specified speed range. It is shown that the optimal per unit slip lies between the limits of zero and r₂/x₂     

高压变频调速中LC滤波电容与异步电机之间的自激

对发生自激时变频装置的滤波器和异步电机的单相等值电路进行分析，推导出自激时LC滤波电容与异步电机频率及电机参数的关系。建立变频装置驱动空载异步电动机JSQ 157－8的仿真系统，通过对封锁脉冲后自激现象的观察，分析了自激幅度与电机参数、滤波电容以及直流电容电压等的关系。仿真结果与正在研制的变频装置脉冲封锁后发生自激的实验结果吻合，表明理论分析与仿真计算正确。最后提出了LC滤波器参数选择及其避免自激的措施。     

ROLE OF TORQUE ANGLE IN INVERTER-FED INDUCTION MOTOR DRIVES

ABSTRACT

It is shown from the induction motor differential equations that changes in load torque, speed reference and torque angle are accompanied by a transient change in the speed of the air-gap mmf. The time constant associated with the torque angle change is different for a voltage source and a current source inverter-fed induction motor. This aspect throws light on the instability of current source inverter-fed induction motor on open loop operation. Evidently, the solution to overcome this instability is to use the torque angle for feedback control. It is proved that torque angle feedback alone is not sufficient for stabilization of the current source inverter-fed induction motor.     

PWM INVERTER FED INDUCTION MOTORS LOSSES EVALUATION

ABSTRACT

In this paper the authors deal with the problems concerning the steady state losses evaluation in medium power industrial induction motors supplied by PWM inverter. They present a method based on the no-load and short circuit tests. This technique seems to be very useful for the good obtained results and because it is quite similar to the standard no-load and short circuit tests used with sinusoidal voltage supply.

The method is based on some simple hypothesis that have been verified during the experimental tests by means of mathematical models. As a consequence, it is possible to compare the no-load and the short circuit tests under sinusoidal and PWM inverter supply considering the same rms fundamental voltage.

The method has been applied to a 7.5 kW induction motor supplied by a prototype PWM Voltage Source Inverter (VSI) modulated with a ramp comparison technique at a 1 kHz switching frequency.

The obtained results could be utilized in order to define some design criteria and the derating for standard induction motors supplied by PWM inverters.     

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.     

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.     

A COMPANION CIRCUIT MODEL OF INDUCTION MOTORS

ABSTRACT

The theory of a companion circuit model of the induction motor is presented. The model comprises an independent current source in parallel with a constant resistance. Accuracy of problem solutions is the same as that obtained from conventional models, but the time of solution is much shorter. This stems from the combined consideration given to the problem formulation and its solution. A companion circuit model can include extra sets of machine coils such as those needed to represent deep-bar effects. Conventional motor models are adequate for single-machine, transient studies. It is for multi-machine studies that the companion circuit concept provides advantages for formulation and solution.     

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.     

The Squirrel-Cage Induction Motor Model and Its Parameter Identification Via Steady and Dynamic Tests

One of the most important bases for designing robust closed-loop controllers applied to induction motor with high performance is establishing its mathematical model and state observers, as well as the parameter identification with high accuracy. In this paper, a step-by-step mathematical model of the squirrel-cage induction motor is described at αβ coordinate frame where the parameters are defined in detailed form; the rotor flux linkages and load torque are estimated via an asymptotic observer; the induction motor parameter identification is performed via a data acquisition board, applying dynamic and steady-state tests. Inductances of the induction motor model are calculated using the proposed relationships between the magnetically coupled circuit and equivalent circuit model. The mathematical model, state observers, and parameter identification procedure of squirrel-cage induction motor are validated via comparison of simulation signals with their corresponding real-time signals. This validation is made experimentally by a steady-state test, where load conditions are changed via a dynamometer which is belt coupled with the squirrel-cage induction motor.