Showing papers on "Induction motor published in 1984"

The Use of Harmonic Distortion to Increase the Output Voltage of a Three-Phase PWM Inverter

Abstract: By adding a measure of third harmonic to the output of each phase of a three-phase inverter, it is possible to obtain a line-to-line output voltage that is 15 percent greater than that obtainable when pure sinusoidal modulation is employed. The line-to-line voltage is undistorted. The method permits the inverter to deliver an output voltage approximately equal to the voltage of the ac supply to the inverter. Thus an induction motor of standard rating with respect to the ac supply to the inverter can deliver very nearly full power at rated speed when supplied from the inverter. This is achieved without pulse dropping or any other form of mode-changing.

Six-Phase Voltage Source Inverter Driven Induction Motor

Abstract: A six-phase six-step voltage-fed induction motor is presented. The inverter is a transistorized six-step voltage source inverter, while the motor is a modified standard three-phase squirrel-cage motor. The stator is rewound with two three-phase winding sets displaced from each other by 30 electrical degrees. A model for the system is developed to simulate the drive and predict its performance. The simulation results for steady-state conditions and experimental measurements show very good correlation. It is shown that this winding configuration results in the elimination of all air-gap flux time harmonics of the order (6v ±1, v = 1,3,5,...). Consequently, all rotor copper losses produced by these harmonics as well as all torque harmonics of the order (6v, v = 1,3,5,...) are eliminated. A comparison between-the measured instantaneous torque of both three-phase and six-phase six-step voltage-fed induction machines shows the advantage of the six-phase system over the three-phase system in eliminating the sixth harmonic dominant torque ripple.

Synchronization of Line-Start Permanent-Magnet AC Motors

Abstract: The line-start PM (permanent magnet) motor is a very high efficiency synchronous motor designed to operate at fixed voltage and frequency from the same power supplies as induction motors. The excitation is provided partly by the magnets, which are mounted in the rotor, and partly by the line current. A squirrel cage is provided to accelerate the motor from standstill when started ``across the line.'' This paper describes the synchronizing process and the characteristics of PM motors that lead to an inherently higher starting capability than that of comparable reluctance motors. The starting performance is described with the aid of computed transient torque/speed and related trajectories. The results have been verified with reference to detailed tests on a 25-hp motor that has been described in earlier papers. Two basic configurations of PM motor are shown in Fig. 1. On the left is a four-pole arrangement with radially magnetized magnets, and on the right a six-pole arrangement with circumferentially magnetized magnets.

Modeling and Simulation of Induction Motors with Saturable Leakage Reactances

Abstract: A new method for the transient analysis of induction machines with saturating leakage reactances is presented. The equations which define operation under this condition are arranged so that the saturation of stator and rotor leakage as well as magnetizing reactance can be readily modeled with three function generators. The method is equally applicable to the analysis of synchronous machines.

Minimizing Induction Motor Losses by Excitation Control in Variable Frequency Drives

Abstract: For a given induction motor under a specified load condition, a combination of stator voltage and frequency exists which results in minimum power losses. This optimal operating point is calculated over the complete speed and torque range using a model of the induction machine including saturation, stray losses, and skin effect. It is shown that substantial power savings can be achieved compared to conventional programmed volts/hertz control and that main flux saturation has a dominant role in determining the optimal operating condition. A detailed analysis of the mechanisms yielding power savings is presented as well as an experimental confirmation of the theoretical results. These results are utilized to study thetinfluence of machine size, rated slip, and other factors on the optimal performance.

A New Slip Frequncy Detector of an Induction Motor Utilizing Rotor Slot Harmonics

Abstract: A method to detect slip frequency from rotor slot harmonics of a three-phase squirrel-cage induction motor is proposed. The rotor slot harmonic voltage Is obtained by summing the three phase voltages, and after being sampled with a multiple of the stator frequency, it is changed into slip frequency waves, from which a voltage proportional to the slip frequency is obtained. Sophisticated sampling techniques allow elimination of the third harmonic voltage induced in the sum of the three-phase voltages and also allow reduction of time constant of the slip frequency detector. Expenmental results show that the slip frequency detector has a good linearity in the range of slip frequency of about -50 to +30 percent of the stator frequency.

An Aggregate Induction Motor Model for Industrial Plants

Abstract: A technique is developed for deriving an equivalent load model to represent the dynamic and steady state effects of a system consisting of induction motors and constant impedance loads interconnected by a network Motor parameters are calculated from standard specifications, and together with network and load data are incorporated into an admittance matrix which is used to define most of the parameters of the load equivalent The inertia and running slip are chosen to minimize the error between the transient response of the system and its equivalent Step responses are calculated using a state approach Adequacy of the equivalent is validated by comparing the response of the original system and the equivalent to simulated bus voltage change, transformer outage, and remote and local balanced faults using a transient stability program

Optimal Efficiency Drive of a Current Source Inverter Fed Induction Motor by Flux Control

Abstract: When an induction motor is driven under light loads, the efficiency can be substantially improved by reducing the air-gap flux of the motor. The air-gap flux can be indirectly controlled by adjusting the stator current and slip frequency in the case of a current source inverter induction motor drive system. The relationship between the stator current and the slip frequency for an optimal efficiency control is derived, and the control loop is suggested. By this method, ten percent or more improvement in the efficiency is obtained at a quarter of the full load. Generally, the reduced air-gap flux may result in undesirable dynamic responses. The small signal analysis is used in order to estimate the transient characteristics. The experimental results indicate a stable operation and a good dynamic response.

Control apparatus for elevator

Abstract: A control apparatus for an elevator comprising a temperature sensor which senses the temperature of the rotor of an induction motor during the stoppage of a cage, and a voltage/frequency control device which calculates the secondary winding resistance value of the induction motor on the basis of the output value of the temperature sensor and which vector-controls a power conversion device by the use of the calculated secondary winding resistance value, so that during the stoppage of the elevator, the temperature of the rotor is measured to alter the secondary winding resistance value necessary for the vector control, whereby the optimum control can be performed.

Power Semiconductor Drives

Abstract: This textbook introduces students to the underlying principles of operation of power semiconductor drives. It explains every facet of application of power electronics to the control of electric motors in industrial drives. The book is primarily intended for B.E./B.Tech. students of Electrical Engineering/ Electrical and Electronics Engineering having courses in Electric Drives/ Power Semiconductor Drives. It will also be highly useful for M.E./M.Tech. students of these disciplines specializing in Power Electronics/Industrial Drives/Electric Drives. The text is divided into eight chapters. The first two chapters cover the control of dc motors by using various kinds of converters. The third chapter focuses on dual converters and various braking techniques. Chopper control fed dc motors are discussed in the fourth chapter. The next three chapters are devoted to control methods for induction motors. The eighth chapter deals with the control of synchronous motor drives fed from VSI converters and cycloconverters. Extensively illustrated, the book contains numerous solved examples throughout the text as well as a variety of chapterend questions to help in comprehending as well as in strengthening the grasp of the underlying concepts and principles. (Goodreads)

Computer Simulation of an Induction Machine with Spatially Dependent Saturation

Abstract: This paper presents a new analog computer model for the simulation of an induction machine which takes into account the spatially dependent main flux saturation effect Using this model of saturation, an unstable operating region for a voltage fed induction motor with high source impedance has been calculated and has been correlated with both test results and the results predicted by the conventional linearized model This study clearly demonstrates an improvement over the linearized model in predicting machine dynamic behavior Because the simulation accurately models large signal as well as small signal behavior it should prove equally useful in predicting transient behavior The manner of dealing with saturation of the magnetizing field presented in this paper can be readily implemented on a digital as well as an analog computer and can also be extended to the study of other electrical machines

The Existence of Large Inter-Bar Currents in Three Phase Squirrel Cage Motors with Rotor-Bar And/Or End-Ring Faults

Abstract: An analysis is developed which describes the existence of substantial inter-bar laminar currents in large three phase squirrel cage induction motors with broken bars and/or rings. Results of experimental measurements are presented which verify the theoretical model. Also the effect of these tangential currents on the production of very large axial vibrations are shown.

Modified current source inverter fed induction motor drive with reduced torque pulsations

Abstract: A new technique for reducing the torque pulsations in a conventional current source inverter fed induction motor drive is presented. This does not attempt to improve the current waveforms, but modifies the airgap MMF directly. This is based on the use of a motor with two sets of balanced phase windings, with a 30 electrical degree phase difference between them, and each set being fed from a conventional current source inverter. The two inverters are further connected in series so that they can operate from the same current source. As a consequence of this arrangement, the voltage rating of the components of each inverter is reduced, along with reduced torque ripple. This scheme has been experimentally verified and compared with the performance of a conventional scheme.

Thermal Protection of Induction Motors Enhanced by Interactive Electrical and Thermal Models

Abstract: Models are of interest to application engineers because they identify important electrical, thermal, and mechanical interactions in an induction motor They provide a format for the parameters which must be obtained The loading and terminal conditions can then be specified and the model state equations used to obtain the thermal limit curves and, what is more important, the time solution for current, torque, speed, and the temperatures of the rotor and stator Adequate protection of induction motors is routinely achieved via locked-rotor, phase unbalance, and overload protection However, conditions of changing load torque, frequent starts, temporary phase unbalance and high inertia loading must often be tolerated Designing protective schemes for these conditions using conventional relays is difficult and sometimes impossible Motor protection is primarily a temperature estimation problem Recognizing that good electrical and thermal models exist leads to their adoption for motor protection so that the heating and cooling process is well represented for virtually all loading and terminal conditions This paper first reviews electrical, thermal, and mechanical models Their parameters are discussed and a novel technique is introduced for accommodating the frequency dependent skin effect of the rotor resistance using a simple speed estimation algorithm The correlation with protection practice is established by using the models to obtain the thermal limit curves for a motor including the relatively recent rotor accelerating time limit The models are then used to analyze conditions of locked rotor, high inertia starting and overload torque

Reduced-Voltage Starting of Squirrel-Cage Induction Motors

Abstract: The most commonly used methods of reduced-voltage starting of three-phase ac squirrel-cage motors are reviewed. They include primary reactor, primary resistors, autotransformer, part winding, wye-delta, and solid state. Other methods are used but less often.

Method for controlling induction motor and apparatus therefor

Abstract: A control apparatus for induction motor comprising an induction motor driven by a power converter, a circuit for producing an effective current command value for the induction motor on the basis of a speed command value and an actual speed value, a circuit for producing a slip frequency corresponding to the magnitude of the effective current command value, and a circuit for producing a primary frequency command value on the basis of the slip frequency and the actual speed value, the output of the power converter being controlled on the basis of the frequency command value, the effective current command value and a given exciting current or voltage command value, wherein the control apparatus further comprises a current component detecting circuit for detecting the primary current of the induction motor so as to produce in the form of a DC signal an actual effective current value which is an effective component of the detected primary current, a first current control circuit for producing an effective voltage command value in the form of a DC signal on the basis of the actual effective current value and the effective current command value, and a converter controlling circuit for controlling the power converter to produce output on the basis of the effective voltage command value, the frequency command value, and a given exciting voltage command value in the form of a DC signal. The current component detecting circuit preferably further produces in the form of a DC signal an actual exciting current value which is an exciting component of the detected primary current, and the controlling apparatus may further comprise a second current controlling circuit for producing the exciting voltage command value on the basis of the actual exciting current value and the predetermined exciting current command value.

A Simple but Reliable Loss Model for Inverter-Supplied Induction Motors

Abstract: A semiempirical induction motor loss model is developed as a function of motor power rating. The aim is the estimation of losses caused by harmonic-distorted (e.g., PWM) current and voltage supplies. The model may consider harmonics between about 100 and 20 000 Hz and is constructed for power ratings between 1 and 1000 kW. Losses in rotor, stator, and iron (including most important stray losses) are separately estimated and suitably combined. This leads to a simple penalization factor for the time-harmonic currents, which is a function of motor size and which is quasi-linearly depending on harmonic frequency. Total losses are then calculated by the superposition of separate harmonic current or voltage effects. The penalization factor is experimentally verified. The importance of iron (plus stray) losses has been clearly shown. The model predictions are in close agreement with loss measurements on inverter-fed induction motors.

Variable speed rotary electric machine

Abstract: A variable speed rotary electric machine comprises a stator composed of a stator core and first and second stator windings wound on the stator core, and a cage rotor mounted rotatably within the stator and composed of a rotor core and rotor conductor disposed in a squirrel-cage configuration. The first stator winding is connected to an AC power supply of a fixed frequency. The second stator winding is connected to a power supply of a variable frequency. The first and second stator windings are so wound as to form, respectively, numbers of poles differing from each other. The rotor conductors of the cage rotor are electromagnetically coupled with the magnetic flux generated by the first and second stator windings, respectively, and so disposed as to form a number of poles which is intermediate between the number of the poles formed by the first stator winding and the number of poles formed by said second stator winding.

Cycloconvertor-excited divided-winding doubly-fed machine as a wind-power convertor

Abstract: The paper describes a slip-ring induction machine operating as a doubly-fed generator above and below synchronous speed. A prime mover simulates a wind turbine by producing a torque increasing in proportion to the square of the speed. This torque is balanced in steady-state operation by the doubly-fed generator. The stator, or secondary of the generator is arranged in two electrically separate, magnetically coupled layers connected to a cycloconvertor operating with continuous circulating current. This reduces the harmonics injected into the supply and prevents line-to-line short circuits under shock conditions. The secondary frequency is locked to the difference between actual speed and synchronous speed. A deadband is built into the frequency demand loop to ensure steady-state synchronous rather than asynchronous performance of the generator. Control of the secondary voltage amplitude enables the system to generate power proportional to the cube of the speed over a wide speed range. Three alternative methods of secondary control are considered. These are: (i) secondary current modification, (ii) a voltage-speed function and (iii) constant secondary current feed. The efficiences and peak power capabilities of the methods of systems (ii) and (iii) are contrasted in operation as a quasi-wind-energy transducerss.

Starting winding switching circuit for single-phase induction motors

Abstract: The switching device of the present invention electrically connects a single-phase induction motor's starting winding to the motor's circuitry upon start-up, and disconnects it once the motor reaches a first predetermined speed. If the motor's speed drops below a second predetermined speed, the switching device reconnects the starting winding to the motor's circuitry until the motor again reaches the first predetermined speed. At start-up, diode bridge D1 turns ON, turning ON SCR S2. With the SCR ON, the diode bridge is short-circuited, drawing a large current through the bridge's a.c. side. This current flows through resistor R8, and the voltage drop across R8 is large enough to turn triac S1 ON. Thus, current flows through starting coil L2. When the motor reaches a first predetermined speed, the voltage across the starting coil is large enough to turn NPN transistor TR2 ON, turning PNP transistor TR1 ON. Accordingly, the SCR turns OFF, eliminating the large current drawn through the a.c. side of the diode bridge, and the triac turns OFF. If the motor speed dips below a second predetermined value, lower than the first, transistor TR1 is cutoff, and the triac subsequently turns back ON until the first predetermined speed is reached.

Scalar Decoupled Control of Induction Motor

Abstract: A scalar control method for an induction motor is described in which the dynamic response is enhanced by a feedforward decoupling network. The scalar control method is inherently simple and does not require intricate signal processing as in vector control methods. The parameters of the adaptive decoupler are solved by off-line computation and can be implemented by using a microcomputer. A preliminary control schemp using a voltage-fed PWM inverter bas been tested in the laboratory, but more investigation is needed to explore fully the potential of the method. The proposed control scheme is expected to give comparable or better performance than the conventional vector control methods.

Microprocessor-Based Optimal-Efficiency Drive of an Induction Motor

Abstract: A method for improving the efficiency of a slightly loaded induction motor is suggested. It is based upon the optimal-efficiency slip tracking by adjusting the voltage to frequency ratio (V/f). It has adopted the converter-inverter fed induction motor drive system. All the control loops are implemented by the Z-80 microprocessor. By this method, 10 percent or more improvement is obtained at a quarter of the full load.

An optimal feedback control for a bilinear model of induction motor drives

Abstract: The use of optimization techniques for the control of drives using a frequency controlled induction motor as an actuator is considered. The approach proposed is based on the choice of a specific control law in the framework of a prefixed class of stabilizing feedback controls. The optimized performance index is obtained a posteriori by applying the Bellmann's principle to a problem with an index in which the term depending on the state is initially unspecified. Successively, the control law is developed, and it is proved how it minimizes a particular index which takes into account both the influence of the error and the control effort. This index has proved very useful in the control choice since it makes it possible to determine a correspondence between the elements of the weighting matrices and the system transient behaviour.

Control system for permanent magnet synchronous motor

Abstract: This disclosure relates to a system for stabilizing a permanent magnet synchronous motor (16) that does not have a rotor starting cage or windings. The system includes a dc source (10), an inverter (13) connected to the dc source for converting the dc to a multi-phase ac, and an ac synchronous motor connected to receive the multiphase ac, the motor being constructed without a starting cage or winding. The system further includes means (22) for sensing variations in the motor power angle, and a control circuit (27,28, 29,33) connected to respond to the variations and to cause the inverter output to vary such as to generate an ac component of torque that leads in phase the power angle variations at the natural frequency of the rotor of the motor. The inverter output may be varied by modulating the applied frequency, the dc bus current to the inverter, or the inverter phase angle.

A Novel Method of Multistage Dynamic Braking of Three-Phase Induction Motors

Abstract: An effective braking system suitable for three-phase induction motor drives is discussed. Braking is achieved in four stages using an electronic switching circuit. Initially, a single capacitor is connected across two of the motor terminals allowing single-phase self-excitation. Following a certain speed drop, a second capacitor is added across the same terminals to sustain self-excitation and reduce the speed further. In the third stage magnetic braking is achieved by short circuiting the third terminal. Finally, the motor is brought to a standstill by dc injection. A method of determining minimum capacitor requirements is presented for both single-phase and symmetrical application. Experimental results are included, demonstrating the validity of theoretical results regarding capacitor requirements, and indicating the effectiveness of the proposed braking scheme.

Considerations in Applying Induction Motors with Solid- State Adjustable Frequency Controllers

Abstract: Considerations in applying ac motors with solid-state adjustable -frequency controllers are discussed, and guidelines. are offered where possible. As a background, three commonly used at drive techniques are reviewed. Test data are provided for 100-hp standard and energy-efficient designs operated on each of the three types of drives.

Dynamic Performance Analysis of Permanet Magnet Synchronous Motors Magnet Synchronous Motors

Abstract: Unlike conventional synchronous motors, a permanent magnet motor develops considerable break torque during its asynchronous mode of operation. An accurate prediction of the run-up characteristics of these motors is quite important. This paper presents the results of digital computer simulation of the transient performance of P.M. synchronous motors. This is achieved by the numerical solution of the machine dynamic equations including the effects of saturation. A discussion is provided to show the influence of various design parameters on the motor dynamic performances. Finally test results are included also to show the close agreement between calculated and measured results.