Showing papers on "Induction motor published in 1980"

Variable-speed switched reluctance motors

Abstract: The paper explores the theory and potential of a family of doubly salient electronically-switched reluctance motors. It is demonstrated that the machine provides the basis for fully-controllable variable-speed systems, which are shown to be superior to conventional systems in many respects. The motor retains all the advantages normally associated with induction motors and brings significant economy in the drive electronics. The basic modes of operation, analysis, design considerations and experimental results from a range of prototype motors up to 15 kW at 750 rev/min are described. The most recent prototype has achieved a continuous rating which is 1.4 times that of the equivalent induction motor.

Improved Reliability in Solid-State AC Drives by Means of Multiple Independent Phase Drive Units

Abstract: Phase redundancy is a proposed technique for improving the reliability of large solid-state adjustable-frequency ac drives. Based on the more general concept of parallel redundancy, this new technique relies heavily on the inherent capability of a general n-phase ac motor to continue operation with (n -1) or less of its stator phases excited. Motor performance degradation which inevitably accompanies such operation is sensitive to a variety of system parameters including the number of stator phases and the type of excitation source. A thorough evaluation of (n - 1)-phase excitation performance characteristics of an n-phase squirrel-cage induction motor is presented in this paper. Under favorable conditions, a large percentage of the motor's balanced excitation rating can be retained during postfault conditions of steady-state (n -1)-phase excitation. The n-phase-drive units must be conservatively designed to withstand transient stresses associated with fault-induced transitions from balanced n-phase to (n-1)-phase excitation. Key analytical results have been experimentally verified by tests conducted on a 5-hp six-phase squirrel-cage induction motor. Results of this investigation support the basic soundness of the phase-redundancy concept.

Parameter Adaption for the Speed-Controlled Static AC Drive with a Squirrel-Cage Induction Motor

Abstract: The performance of speed-controlled induction motor drives, without a direct sensing of the flux, depends heavily on the accuracy with which the motor parameters are known. They change widely with the temperature, frequency, and current amplitude. With a control based on rotor position measurement and inner current control loops, the rotor resistance is the most essential changing parameter. A method of automatic adaption of the control to the changes in this parameter is presented. The proposed strategy is based on the measurement of only motor voltages and currents and is implemented by analog means. It does not make use of transducers or probes to measure the temperature or the flux in the motor.

Field-Oriented Control of a Standard AC Motor Using Microprocessors

Abstract: Field orientation has emerged as a powerful tool for controlling ac machines such as inverter-supplied induction motors. The dynamic performance of such a drive is comparable to that of a converterfed four quadrant dc drive. The complex functions required by filed-oriented control may be executed by microprocessors on line, thus greatly reducing the necessary control hardware. It is shown that the flux signals may be derived from sensing coils or, with some compromise in performance, from the stator voltages and currents. The speed signal is obtained from a digital tachometer. Results from a 2-kW experimental drive are given.

An Approach to Flux Control of Induction Motors Operated with Variable-Frequency Power Supply

Abstract: A new speed control system for induction motors has been developed which is capable of controlling with quick field weakening and superior response and stability. This method is to control the stator current as a vector quantity on the basis of slip frequency control. More specifically, it is designed to calculate the commanded stator current of the induction motor by corresponding to flux and torque commands on the basis of motor constants and use the calculated commands to control the stator current.

Improvement in Energy Efficiency of Induction Motors by Means of Voltage Control

Abstract: It has been estimated that electric motors in the U. S. consume approximately 64% of all the electric energy generated. Also, over the past 12-20 years, the efficiencies of electric motors under 10 kW (~15 hp) have degraded significantly, though the trend toward lower efficiencies appears to be reversing. Very substantial energy savings are possible in lightly loaded induction motors by means of controlling the applied voltage. Tests are conducted on a fractional horse-power motor, and several voltage control arrangements consisting of SCRs are compared in their ability to improve the motor efficiency, and in terms of the amount of harmonic currents generated.

Induction disk motor with metal tape components

Abstract: An induction motor of the squirrel cage type is disclosed. The stator body and rotor body of the motor are each disclosed as being made of a coil of concentric layers of a thin metal tape which is slotted to receive the rotor and stator windings. The motor is similar to a conventional disk type motor except that the secondary, instead of being a solid copper or aluminum disk, is a coil of concentric turns of notched metal tape which improves the efficiency by reducing the effective air gap. A method of manufacture of the coil of tape is disclosed wherein identical notches are formed in the tape with a progressively increasing spacing between the notches which permits the notches to come into radial register with one another to form a slot in the end of the stator or rotor body.

Development of a High Speed 2-Pole Permanent Magnet Synchronous Motor

Abstract: A high speed, 2-pole permanent magnet synchronous motor with a rated speed of 12,000 r/min and rated out put of 1.0 kW has been developed. Features of the new motor are described in this paper. An improved method of calculation for synchronous reactance is proposed, and a comparison is made between measured and calculated values.

Field analysis for rotating induction machines and its relationship to the equivalent-circuit method

Abstract: This paper presents a field analysis for rotating induction machines which includes the effects of rotor skew, and accurately models the discrete nature of the rotor curent. It is verified by comparison with the conventional equivalent-circuit method, and by using it to derive the equivalent-circuit for a balanced 3-phase skewed-rotor induction machine.

Power factor controller for induction motor

Abstract: A phase-triggered, gate-controlled AC semiconductor switch, in series with an induction motor and its AC supply, optimizes power flow to the motor under changing mechanical load conditions by varying the amount of supply voltage applied to the motor over each half-cycle of the AC supply. The triggering point of the switch relative to the preceding zero crossing point of the supply voltage, that is, the switch firing angle or delay angle, is varied as a function of mechanical loading on the motor by means of a load current-induced feedback voltage augmenting to a varying degree the charging rate of a capacitor which triggers the semiconductor switch into conduction. Under increasing mechanical load conditions, the feedback voltage increases in proportion to the increasing load current, the increasing feedback voltage accelerating the charging rate of the capacitor to trigger the switch into conduction at a reduced firing angle, wherein power flow to the motor is increased. Conversely, under decreasing mechanical load conditions, the feedback voltage decreases in proportion to the decreasing load current, the decreasing feedback voltage decelerating the charge rate of the capacitor to trigger the switch into conduction at an increased firing angle, wherein losses caused by reactive current in the less-than-fully-loaded induction motor are reduced with a resultant optimization of power factor.

A High-Performance Controlled-Current Inverter Drive

Abstract: A production variable-frequency drive is described which uses an induction motor and a controlled-current inverter. The control loops of the drive have been arranged so that the performance of the drive is extended to zero speed and to the theoretical upper limit speed. Operating modes include torque smoothing by programmed dc link current, pulsewidth modulated (PWM) current shaping, and flux-controlled constant horsepower operation.

Load responsive control system for constant speed induction motor

Abstract: A voltage control system for an induction motor, consisting of a SCR AC voltage controller with sensing and control circuitry, adjusts the motor voltage in response to the load torque demand, thereby minimizing the motor's magnetizing current and its associated losses. The motor displacement power factor angle, which is responsive to load torque, is sensed by directly sensing the motor voltage, deriving its fundamental or line frequency component, and phase-comparing that component with a similiarly derived fundamental component of the motor current. The resulting displacement power factor signal is amplified, together with a stability augmentation signal, to form a phase delay command signal for the AC controller. The stability augmentation signal, representative of the blocking voltage across the AC controller SCRs, is formed by rectifying the 180 Hz single phase sum of the three motor voltage signals.

Stabilization of Controlled Current Induction Motor Drive Systems via New Nonlinear State Observer

Abstract: In this paper a new bilinear and nonlinear second-order state observer which is globally asymptotically stable is constructed to estimate the unmeasurable state variables. Then an unstable controlled current induction motor drive system which cannot be stabilized by a linear state observer is successfully stabilized by feeding the reconstructed state variables from the nonlinear observer to the frequency control channel. This scheme is easily implementable, resulting in an asymptotically stable overall closed-loop system. These results are numerically verified by simulation.

Squirrel-cage rotor having end rings of double structure

Abstract: A squirrel-cage rotor for an induction motor is disclosed. In this rotor, each of end rings electrically connecting the associated ends of the conductor bars received in the slots of the rotor core comprises a first ring portion disposed in contact with the associated end face of the rotor core, and a second ring portion disposed on or coupled to the first ring portion through a member of a magnetic material in the axial direction of the motor, this second ring portion having a sectional area smaller than that of the first ring portion when the section is taken in a direction orthogonal with respect to the axis of the motor.

Three phase motor oscillatory servo control

Abstract: The rotor of a brushless DC motor is monitored continuously, and successive positions thereof are encoded in the form of digital counts. The count is continuously converted to analog form, and is compared with an analog reference signal, to determine the position error, and hence the speed error, or the motor relative to the desired constant speed reference. The error differential is suitably converted back to digital form to provide the motor power/drive amplifiers with sufficient electrical drive for the degree of correction which must be made. The digital position count from the counter is also coupled to a memory, which maintains in storage representations of position, and torque characteristics of the motor. Hence, based on these stored quantities and upon the actual motor parameters as exemplified by the present position, the memory issues control signals, that is timing and directional commands for correction of the motor speed.

Power factor control of a three-phase induction motor

Abstract: First and second input currents to a three-phase AC induction motor of either delta or wye winding configuration are directly regulated by a pair of phase-triggered, gate-controlled, semiconductor switches series-inserted between the motor and two phases of its three-phase AC power source, the third input current being the Kirchoff resultant of the two regulated input currents. The half-cycle firing points or firing angles of the gate-controlled switches are varied together to apply more or less power to the motor as a function of mechanical load to optimize the power factor of the motor. Voltage imbalances in the motor windings caused by directly regulating only two of three input currents are tolerable due to the current limiting effect of the gate-controlled switches when the induction motor is at less than full mechanical load, such current limiting minimizing heat losses (I2 R) caused by the voltage imbalance condition.

Electric motor drive with infinitely variable speed transmission

Abstract: A drive system adapted for use in motor vehicles comprises an infinitely variable speed drive transmission coupled to a DC motor, and the speed ratio of the transmission is controlled by a speed-responsive flyweight or governor so as to maintain the DC motor at its most efficient operating level.

Liquid cooling for induction motors

Abstract: An induction motor is disclosed which utilizes a liquid in intimate contact with the rotor and stator conductors for cooling and yet minimizes the disadvantages of high rotational drag losses associated with conventional spray cooled motors. Cooling liquid is conducted through a hollow rotor shaft and directed to a cavity at the center of the magnetic length of the rotor. The cavity is formed by separating two adjacent rotor laminations. The cooling liquid flows axially from the central cavity toward the rotor ends through slots which contain the rotor conductors. A sealing band is provided around the rotor laminations to prevent cooling liquid from entering the air gap between the rotor and the stator.

Stability Analysis of Induction Motor Drives Using Phase-Locked Loop Control System

Abstract: This paper presents the analysis of an induction motor drive using a phase-locked loop speed control system. A linear continuous model of the drive is developed and the system response is analysed using conventional root locus techniques. Various compensating ``filters'' and feedback signals are considered and the need for addition of derivative feedback is shown. A sampled data model is used to study the effects of discrete phase detector output. Stability limits on speed are predicted. A drive was implemented and experimental results are presented to verify theoretical predictions.

The Effects of Neglecting Stator Transients in Induction Machine Modeling

Abstract: The dominant eigenvalues of the linearized reduced order model of an induction machine in which stator transients are neglected are compared with the dominant eigenvalues of the linearized full model. How closely the eigenvalues agree is shown to depend both on machine parameters and load inertia. Computational results indicate that in most situations a very simple criterion, (RsRr/X22) < (1/10K?), can be used to s rZ check whether the reduced order model is accurate (K? being the ratio of the rotor transient time constant to the static electromechanical time constant). An intuitive understanding of when and how the dominant eigen- values of the reduced order model differ from those of the full model is obtained utilizing root loci plots. An examination of the accuracy of the zeros, and hence the step response, is also included.

Simplified power factor controller for induction motor

Abstract: In the past duty cycle control for power optimization of induction motors has been accomplished with a series-inserted, phase triggered thyristor and a motor voltage-current phase angle measuring control circuit. These type of systems are undesirably complex and costly. In the instant invention power optimization is effected by utilization of a control voltage generated by the freewheeling induction motor (20) on line (16) during non-conduction periods of a series-inserted thyristor (60). The thyristor (60) firing angle is varied by the control voltage augmenting to a varying degree the charging rate of a capacitor (44) which triggers the thyristor (60). Under increased mechanical load, the freewheeling induction motor (20) control voltage decreases, the decreased control voltage accelerating the charging rate of the capacitor (44) and thus causing the thyristor (60) to conduct at a reduced firing angle so more power per cycle is delivered to the motor (20). The reverse effect occurs when the mechanical load is decreased. Therefore, the instant invention is a simpler and less costly control circuit to optimize the power factor of an induction motor.

Digital induction motor control system

Abstract: A digital self-calibrating power factor controller for an AC induction motor. During start-up a first number corresponding to the actual phase angle between motor voltage and current is determined and compared with a second number corresponding to a desired delay in energizing the motor. The second number is varied until both numbers are approximately equal. A third number corresponding to a desired phase angle is determined and stored and the system switches from start-up to run. The first number corresponding to the actual phase angle is now compared with the third number corresponding to the desired phase angle. The second number corresponding to a desired delay is now varied with motor load so as to keep the actual phase angle equal to the desired phase angle.

Motor control system for a single phase induction motor

Abstract: A single phase induction motor control system employs power line assisted starting and runs at higher than power line frequency from an electronically generated inverter supply. This inverter supply is employed to provide an out of phase mains frequency signal to the run winding during starting in order to create the rotating magnetic field needed to start the motor. After the motor has started, the power line supply is disconnected from the start winding and the inverter supply frequency is increased gradually to a final value corresponding to the desired operating speed. In this system no phase shifting capacitors are needed to provide the out of phase starting voltage and the run winding is optimized for running conditions.

Load state control for an asynchronous machine fed by a converter

Abstract: A control unit for regulating an asynchronous motor supplied with power from a three phase network by a line-controlled power converter which is DC coupled to a self-commutated inverter has a function generator and a current regulator which controls the stator current of the motor by the controlling rectifier valves in the inverter. Control of the stator current is a function of a predeterminable value of flux fed into the function generator. In a parallel control system, an actual-value computer and a load state control regulate the stator frequency by generating a signal for controlling the self-commutating converter as a function of the actual values of the stator current, the stator voltage, and a value calculated from the function generator input variable. The computer forms signals corresponding to the amplitude of the flux vector, and to a stator current component perpendicular to the flux vector. A variable derived from the predeterminable variable is applied to the load state control as a reference value. Fall-out-proof, low oscillation, speed control is effected from low angles to nearly 90°.

Electric control apparatus of induction motor

Abstract: An electric control apparatus of an induction motor is provided with a flux current controller for controlling the flux current of the motor and a secondary current controller for controlling the secondary current of the motor. A pulse generator circuit is disposed to control the amplitude, frequency and phase angle of the primary current of the motor according to output signals of the flux current controller and secondary current controller. The primary voltage and frequency to be applied to the motor are controlled by pulse signals from the pulse generator circuit. This pulse generator circuit includes a primary voltage setting zone for setting the primary voltage of the induction motor and a primary voltage detecting zone for detecting the primary voltage of the motor. A voltage regulator is disposed to put out a signal equivalent to the change of the secondary resistance of the induction motor according to the deviation of the voltage between the primary voltage detecting zone and the primary voltage setting zone. A correcting controlling zone is disposed in the pulse generator circuit to perform a controlling action of correcting the frequency, which is one of the control objects of the pulse generator circuit, according to the output signal of the voltage regulator.

Variable speed electric machine having controlled magnetic flux density

Abstract: Induction motors traditionally have a high breakaway torque to running torque ratio to prevent motor damage from excessive current as the motor slows down under a heavy load. Such design characteristic results in motor flux density being maintained during normal operation at non-optimum levels. Accordingly, the motor size must be substantially larger than would theoretically be necessary in an ideal motor in order to obtain the desired output horsepower. In the invention a capacitor (16) is connected in series with each stator main winding (10), (12), (14). The voltage across the capacitor (16) together with the motor input voltage periodically causes the volts-second capacity of the stator core to be exceeded causing a periodic change from high to low flux density. The average flux density remains high without the danger of high input voltages resulting in extremely high input currents. Control windings (18), (20), (22) are wound on the stator core adjacent to each stator main winding (10), (12), (14) thus creating main and control winding pairs. The control windings (18), (20), (22) are wound in the opposite direction from the main windings (10), (12), (14) so that the main winding current and the control winding current of each pair is in-phase at no load and increasingly out of phase as the load increases. This results in a low flux density at low load and increased flux density at higher loads. The flux density is optimized for the particular load condition which is turn minimizes the line current for a particular load. Thus minimizing the motor size required for a desired horsepower.

Characteristics of a new AC motor making good use of parametric oscillation

Abstract: This paper is a description of the operating principle and the construction of a new AC motor making good use of parametric oscillation. This motor is constructed by two magnetic cores of U-shape, a stator of ring form, a cage rotor of usual induction motor and two windings. It has a number of excellent operating characteristics.

Power Converters for Feeding Asynchronous Traction Motors of Single-Phase AC Vehicles

Abstract: Asynchronous induction motors are very well suited to powerful traction drives. For electric locomotives and motor coaches with single-phase supply, a power conversion on the vehicle is necessary. Three different types of static power converters for this application are described. Indirect ac converters with direct voltage link have been developed successfully in the past. For indirect ac converters with direct current link some problems are discussed. At last a self-commutated direct ac converter with suppressed dc link is presented.

Control system for induction motor-driven car

Abstract: A control system for an electric car driven by an induction motor which is supplied with electric power of a variable frequency and a variable voltage from an inverter comprises means for detecting the car speed, means for setting a slip frequency of the motor, a frequency command generator, control means for controlling the output frequency of the power converter in accordance with the frequency command and controlling the output voltage of the power converter, a current command generator, and a voltage command generator. The output voltage of the power converter is controlled in accordance with selected one of the current command and the voltage command while being limited by the other command.

DC to AC inverter and motor control system

Abstract: This relates to a low cost reliable controller which may be used in conjunction with induction motors or, more generally, to generate AC power from a DC source. The system utilizes a microprocessor in combination with low cost parallel transistors to provide the control function. A feedback module monitors the actual rotor speed and conveys this information back to the microprocessor. A voltage boost module may be used in combination with the microprocessor and switching circuits to optimize the overall efficiency of the system. The microprocessor computes slip and controls the voltage drive in order to further optimize efficiency of the system as a function of motor speed. Both the footfeed voltage and boosted voltage are analog voltages and are applied to an A/D converter. The output of the A/D converter presents a digital representation of the footfeed voltage or boost voltage to the microprocessor.