Showing papers on "Induction motor published in 1978"

Speed Control of a Single-Frame Cascade Induction Motor with Slip-Power Pump Back

Abstract: This paper describes an analytical and experimental study of a self-cascade single-frame brushless induction motor, using a rectifier- inverter to control speed by slip-power pump back to the line. Steady- state analyses of asynchronous and synchronous performance and test results of a special machine wound for the study are presented. The effect of machine parameters, windings, and construction is discussed. The performance and rating of the brushless cascade machine are found to be equivalent to the slip-ring induction motor or wound-field synchronous machine built into the same frame.

Synchronized induction motor

Abstract: A synchronized induction motor comprises a stator including a cylindrical armature core having an armature winding wound thereon for generating a rotating magnetic field, a cylindrical housing for housing the stator therein, end brackets mounted at opposite open ends of the housing and having a bearing mounted at a center portion thereof a rotor shaft concentrically arranged in the stator axially of the armature core and rotatably supported by bearings, a rotor core mounted concentrically with the rotor shaft on the rotor shaft and magnetically coupled to the armature core through an air gap, end plates mounted to sandwich the rotor core, starting secondary conductors arranged axially of the rotor shaft in the vicinity of an outer circumference of the rotor core and adapted to cooperate with the stator which is held by the end plate to form an induction motor, end rings for shorting the ends of the secondary conductors on the end plates, balance rings mounted on the rotor shaft in the vicinity of the bearings, sumarium-cobalt split-type permanent magnets arranged around the outer circumference of the rotor core axially of the rotor shaft, and an epoxy fiber impregnated glass fiber tape or stainless steel tape for holding the permanent magnets on the rotor core. The permanent magnets are magnetized after they have been mounted on the rotor core.

Protective control circuit for induction motors

Abstract: A solid state electronic circuit for protecting a single phase induction motor against excessive loading by comparing motor start winding voltage with motor source voltage is disclosed, wherein the circuit automatically removes the motor from its driving source upon the occurrence of such excessive loading. An additional feature includes comparing start winding voltage with source voltage to remove the motor from its driving source upon the occurrence of excessive start winding voltage and corresponding excessive high motor speed. A motor starting circuit to permit the start winding voltage to rise to its normal running level and a time delay restarting circuit to permit the motor to automatically restart after elapse of a selected lock out period following removal of the motor from the source due to insufficient or excessive loading is also provided.

Analysis of Winding Failures in Three-Phase Squirrel Cage Induction Motors

Abstract: Every motor user is faced with the fact that someday his motor will fail. Due to the destructive nature of most failures, it is not easy to determine the cause. The purpose of this paper is to introduce a procedure for analyzing these failures and determining the cause so that further steps can be taken to eliminate them.

Spindle drive system

Abstract: A floppy disk drive system employs an inside-out DC motor whose centrally located stator is mounted directly to the chassis The motor has a tubular rotor that encircles the stator and it is supported co-axially with the stator by the rotary disk drive spindle A timing and commutation disk is mounted directly on the rotor and, together with speed control and commutation networks, maintains uniform motor speed

Energy economizer for induction motors

Abstract: A standard, unmodified AC induction motor has its stator winding energized from a sine wave power source through a signal-responsive wave modifier operative to control the portion of each cycle of the swine wave which is coupled from said source to the stator winding. Load detecting means, comprising a comparatively small AC generator coupled to the rotor of the motor, produces a control signal, varying with variations in the load on the motor, for controlling the wave modifier to increase the field density of the stator winding with increases in load on the motor, and to decrease the field density of the stator winding with decreases in said load.

Control method and means for efficient operation of brushless d-c motors over a wide range of operating conditions

Abstract: Method and apparatus for efficient operation of a brushless d-c motor are shown. A brushless d-c motor comprises, essentially, a motor drive source, such as a d-c to a-c converter, in combination with a conventional brushless a-c machine. Generally, the brushless a-c machine includes a polyphase stator for the production of a rotating electric field, and a rotor that produces mechanical power from the rotating field without the need for sliding electrical contacts. For induction motors, the rotor phases are short-circuited and rotor currents are produced by allowing the rotor to "slip" with respect to the rotating stator field, the resulting flux variations in the rotor thereby inducing rotor currents. Motor speed is controlled by frequency control of the a-c output from the motor drive source. The present arrangement includes an efficiency controller responsive to motor input current and voltage for producing a first signal related to motor impedance, and a second signal related to motor impedance required for maximum motor operating efficiency. The difference between said first and second impedance related signals is used to control the motor input voltage for efficient motor operation over a wide range of operating speeds and torques.

Multilayer approach to the analysis of single-sided linear induction motors

Abstract: Among linear electric motors, single-sided linear-induction motors (s.l.i.m.s) with sheet on solid-back-iron secondary have been generally preferred for low-speed drives and, in the last few years, they are considered one of the most probable alternative for the propulsion of some of the medium and high speed vehicles of the near future. Although a precise assessment of the performance of s.l.i.m.s is necessary, this seems to be a difficult task because of the presence of longitudinal-, and transverse-edge effects together with skin, and saturation effects in the back iron of the secondary. The literature in the field ignores one or two of the above mentioned phenomena. The present paper strives to present a complete theory of s.l.i.m.s and at the same time takes into account the specific phenomena mentioned earlier. The theory is based on the double Fourier series decomposition of the primary magnetomotive force (m.m.f.). The back iron of the secondary is notionally split into thin sheets of constant permeabilities which are determined by means of an underrelaxed iterative procedure. The theory has shown good agreement with results obtained from tests performed on an arch-type primary with a large diameter-wheel secondary.

Gain normalization technique for controlled current induction motor system

Abstract: An a-c induction motor powered from an adjustable frequency and adjustable magnitude power source is provided with a feedback control system whose gain is varied as a function of the magnitude of flux developed in the motor in order to normalize system response throughout the motor operating range. The control system is a two-loop system in which one loop adjusts excitation frequency and the other loop adjusts excitation magnitude with the excitation frequency loop being responsive to a torque command signal and a torque feedback signal to generate an error signal which is utilized to adjust the excitation frequency of the power source. System gain is varied by modifying the error signal as a function of the magnitude of flux developed in the motor. Preferably this modification is performed by dividing the error signal by a signal representative of the magnitude of motor flux.

Method of testing induction motors

Abstract: A method is provided for testing induction motors, particularly single-phase fractional horsepower motors, which enables routine testing of all motors in production for both starting and running torque and other desired characteristics. The method consists essentially of applying power to the motor for a very short period of time, such as three or four cycles of the supply voltage, then interrupting the power supply and immediately measuring the instantaneous speed by observing the induced voltage from the deenergized motor terminals. The torque then is verified from the change in speed over this short period. Both starting and running torques can be tested very quickly in this manner by means of solid-state control and computing devices, without connecting anything to the motor other than the power leads. Other desired characteristics of the motor can also be readily determined.

Motor having electronically switched stator field current and integral torque control

Abstract: An electric motor having a construction to insure full utilization of driving currents containing significant harmonic energy. The stator field current may be provided from a multi-phase source or switched electronically through optical sensing of rotor position to eliminate mechanical commutation. Motor torque is made variable by controlling the duration of field current pulses supplied to the stator winding, which also permits variable regenerative dynamic braking of the motor.

Energy economizing AC power control system

Abstract: An induction motor has its stator winding energized from a sine wave power source through a signal-responsive wave modifier operative to control the portion of each cycle of the sine wave which is coupled from said source to the stator winding. The induction motor includes a squirrel cage rotor which carries an additional windings operative during rotation of the rotor to generate a polyphase AC voltage having an amplitude which is proportional to the load on the motor, and the AC voltage so generated is rectified to produce a DC signal which is coupled to a DC amplifier which in turn produces a control voltage for controlling the wave modifier.

An induction motor model with deep-bar effect and leakage inductance saturation

Abstract: A two-phase dynamic induction motor model is derived which includes the effects of rotor bar eddy currents and leakage inductance saturation. The model is based on approximate analysis of the air-gap and slot electromagnetic fields which leads directly to lumped circuit equations. New expressions are given for the variation of the zig-zag and slot leakage inductance with saturation. — The model is applied to the calculation of both steady state and dynamic characteristics for a large induction motor.

Constant Torque Operation of Induction Motors Using Chopper in Rotor Circuit

Abstract: A novel control scheme is investigated for operating induction motors in the constant torque mode. The basic control schemes and analysis of the steady-state performance of the system are presented. Circuit models are used to predict the performance characteristics. A new dc dynamic braking method is proposed and studied that provides very fast braking. Experimental results are presented to verify the theoretical predictions and demonstrate the feasibility of the control schemes.

A comparison of linear induction and linear synchronous motors for high speed ground transportation

Abstract: Preliminary designs for full-scale (3750 kW) linear synchronous traction motors of both the claw pole (Lundell) and the homopolar inductor types are compared with the LIMRV motor, a full-scale linear induction motor which has recently undergone high-speed testing. These designs show the homopolar inductor to be the favored linear synchronous motor with a predicted improvement in power factor, efficiency, and power density when compared to the linear induction motor. No-load test results from a 112 kW homopolar inductor test motor are presented which in general confirm the predicted advantages of the homopolar inductor design.

Digital tach and slip signal motor control

Abstract: The rotor speed of a three phase induction motor is detected by a two channel pulse tachometer, which generates per revolution of the rotor 384 signals that are summed with a slip rate command signal in the first of two successive digital counters. The counters divide the 384 signals/revolutions by 192, thereby producing a four bit counter output which cycles twice per revolution of the rotor. The four bit output is decoded by a read-only memory which produces six output signals each half revolution of the rotor. The read-only output signals are applied to an inverter circuit which controls the gating of the SCR's in the lines of the stator winding of the motor. Gating circuits associated with the counters prevent undesirable simultaneous triggering of count up and down terminals, respectively, on the counters. Also balanced choke coils are employed in two of the stator winding leads between the inverter and the rectifier which supplies DC current to the inverter-controlled SCR's.

Motor/brake transitioning for an inverter driven a-c induction motor

Abstract: Dynamic response of an a-c induction motor control system including an adjustable frequency and adjustable magnitude power source is made more stable during the transition from a motoring to an electrical braking mode by modifying the system characteristics as a function of rate of change of motor flux and torque magnitude during electrical braking. The control system responds to a torque command signal and a torque feedback signal to generate an error signal which controls the frequency of the excitation supplied to the motor and thus the torque developed by the motor. During electrical braking this error signal is modified as a direct function of the rate of change of motor flux and as an inverse function of the magnitude of torque developed by the motor. During the transition from motoring to electrical braking, when the system tends to be unstable, the rate of change of flux is relatively high while the motor torque is at a relatively low value. Accordingly, the error signal becomes very large in magnitude and rapidly forces the control system and motor out of the transition zone into a more stable operating zone. Once stabilized, modification of the error signal becomes negligible.

System for controlling a separately excited constant load DC electric motor

Abstract: A separately excited constant load DC electric motor is controlled in resse to a source of current for the desired motor speed. Current from the source applied to the motor armature is modified by a motor loss simulator circuit responsive to the source. The circuit simulates the losses the motor is expected to have in response to the current derived from the source, whereby the actual motor speed corresponds with the desired motor speed despite the loss. The losses are simulated during acceleration and deceleration as well as steady state intervals of the current source, which can be actuated to drive the motor in both directions.

Electric drive with a universal and induction motor combined on a common lamination stack

Abstract: In an induction and universal motor combined in a common lamination stack and supplied from a single phase line in line with a single armature winding system common to universal commutator motor as well as to induction motor operation, there are connected to the same segments of the commutator a crossed lap winding and an uncrossed lap winding, the coil span of which corresponds approximately to one pole pitch of the low pole and, in particular, two pole commutator stator winding and to an uneven integral multiple of the high pole induction motor stator winding, to provide a motor particularly suited for driving automatic washing machines.

Control system for stepping motors, a method of operating stepping motors, and a method for selecting current patterns for stepping motors

Abstract: An open loop control device and method are provided for stepping motors. By energizing a motor so that the rotor motion is the result of a revolving field which is of piecewise constant speed and uniform field strength, the rotor can be brought to a stop at any desired position. Such position can be the same as or different from the conventional full-increment or half-increment detent positions of the motor. This control method and device guarantee that there is no oscillation when the rotor reaches its final position. The field windings are energized in sequential manner and such that the resultant field takes into account the magnetic characteristics of the motor. The revolving field can be initially adapted to produce, in one case, an angular velocity of half the desired speed for purposes of accelerating the rotor. After one-half of a resonant period has elapsed, the rotor is accelerated to the desired speed. At this time, the speed of the field is doubled and the rotor fully synchronized therewith. When the rotor is to be stopped, the field velocity is switched to an angular velocity equivalent to that of the acceleration velocity which is half the constant speed velocity and the rotor therefore overshoots. Half of a resonant time period later, the rotating field is stopped and the rotor comes to a standstill without oscillation since the field is precisely aligned with the rotor at the instant of stopping. Also, a method is provided for establishing current forms or patterns for the windings of a multi-phase stepping motor to provide the uniform revolving field taking into account the magnetic characteristics of the motor. This method comprises, for each of the pairs of windings which are sequentially effective to drive the rotor of the stepping motor, the steps of driving one winding of the pair with maximum running current and measuring rotor stiffness at the resultant detent position, and thereafter passing a relatively small current through the other winding of the pair and reducing the current through the first winding to displace the rotor to a position which is a fraction of a distance towards the next detent position. These two currents are adjusted to obtain a rotor stiffness equal to the first rotor stiffness while maintaining rotor position. Subsequent steps involve sequentially displacing the rotor and repeating the process to obtain a current curve which will generate the aforesaid revolving field with constant velocity and uniform strength despite magnetic characteristics of the components of the stepping motor involved.

Power and Current Pulsations of an Induction Motor Connected to a Reciprocating Compressor

Abstract: The influence of a periodic pulsating torque variation on a polyphase induction motor is described. A calculation method is outlined to predict the current, power, and torque pulsation along with the effect on power factor, slip, and efficiency. The calculation method is compared with tests and a digital solution of the differential motor equations.

Linear motor drive system for continuous-path closed-loop position control of an object

Abstract: A precision numerical controlled servo-positioning system is provided for continuous closed-loop position control of a machine slide or platform driven by a linear-induction motor. The system utilizes filtered velocity feedback to provide system stability required to operate with a system gain of 100 inches/minute/0.001 inch of following error. The filtered velocity feedback signal is derived from the position output signals of a laser interferometer utilized to monitor the movement of the slide. Air-bearing slides mounted to a stable support are utilized to minimize friction and small irregularities in the slideway which would tend to introduce positioning errors. A microprocessor is programmed to read command and feedback information and converts this information into the system following error signal. This error signal is summed with the negative filtered velocity feedback signal at the input of a servo amplifier whose output serves as the drive power signal to the linear motor position control coil.

Control device of AC motor

Abstract: In a control device of an AC motor wherein a torque equivalent to that of a DC motor is created by controlling the instantaneous values of its stator current, or in a vector control device, signals from a position detector such as a resolver coupled to the AC motor are utilized to form stator current instruction signals and to provide rotation position feed-back signals and rotation speed feed-back signals for the AC motor, thereby to perform precise servo-control.

Low cost, variable speed, constant torque induction motor drive

Abstract: A low cost, small rating AC motor drive includes an inverter in which static controlled switches are in two sets associated with opposite poles and controlled in such a way that current continuously fed is sensed relative to one set for feedback current sensing and that the switch current is modulated in the other set in order to regulate the motor current. When starting, or overloaded, the motor drive speed is automatically reduced under air gap motor sensing.

Over-power safety device for motor driven system

Abstract: A safety device and method for detecting over-power conditions on the chassis of a motor driven system interrupts energization of the system when the voltage differential between the system chassis and earth ground exceeds a selected value. The device is especially beneficial for systems utilizing multi-phase induction motors in which current sensing safety devices cannot effectively detect all over-power conditions. The safety device utilizes a fuse and a motor control relay such that, upon the occurrence of the over-power condition, the fuse is rendered non-conductive, opening the motor control relay.

Electric two motor drive

Abstract: An electric two motor drive is disclosed in which the field winding of a commutator motor having few poles and the stator winding, distributed in slots, of an induction motor having a larger number of poles are both arranged on a common stator lamination stack. The field winding is wound around part of the circumference of the stator lamination stack in the manner of a concentrated ring armature winding. Either a closed or an open stator lamination stack may be provided. The invention is applicable particularly to a two speed motor drive for an automatic washing machine having a single lamination stack for the series and induction motor windings.

Capacitor Starting of Large Motors

Abstract: The basic requirements of a capacitor starting system for use in reducing voltage flicker during start-up of large induction motors are presented. Flicker calculations, control circuits, switching requirements, overstressing, and flicker reduction are discussed along with test results from several installations on the Houston Lighting and Power Company system.

Analysis and control of torque pulsations in current fed induction motor drives

Abstract: Three types of feedback compensation schemes are described which can be used to reduce the torque pulsations which normally occur when induction machines are supplied from a current source inverter. The approach is verified both by a detailed computer simulation and also by test results from an actual system. Limitations of the method near zero slip frequency (no load) is discussed and a means suggested for elimination of the problem.

Spatial Fourier transforms: a new view of end effects in linear induction motors

Abstract: Fourier-transform theory is used to solve the longitudinal-edge-effect problem in linear induction motors, for constant-current conditions. Inversion of the Fourier transform is obviated by employing Parseval's theorem; calculations are thus considerably simplified. Experimental confirmation is given, together with an approximate method for sketching the thrust/slip curve. The ratio (goodness factor/pole pairs) is shown to be important.

An Adjustable-Speed Induction Motor Drive with a Cycloconverter-Type Thyristor-Commutator in the Rotor

Abstract: An adjustable-speed drive comprising a slip-ring induction motor and a cycloconverter-type thyristor-commutator in its rotor circuit has been developed. The thyristor-commutator acts as a frequency-changer like a conventional commutator in a stator-fed ac commutator motor, converting line-frequency injected voltages directly to slip-frequency at the rotor terminals. The circuit permits a reversible power flow naturally, and speed-control is possible for subsynchronous as well as supersynchronous operation by controlling the injected secondary voltage. A rotor position-detector is used to switch the thyristor configuration in a sequential manner to generate an output voltage having a predominant slip-frequency component. The control logic and triggering circuit developed for the experimental drive are described in some detail. Experimental results as obtained with a laboratory model are presented together with some results of computer simulation of the drive system. Major limitations of the scheme and the scope for improvement are discussed.