Showing papers on "Induction motor published in 1981"

Application of Sliding Modes to Induction Motor Control

Abstract: The results of the research concerned with the problem of induction motor control system synthesis using variable structure systems theory is presented. The procedure of control systems synthesis for the control of position speed and torque is given, as well as basic experimental results and problems related to realization of the proposed control algorithms.

Inverter drive for switched reluctance motor: circuits and component ratings

Abstract: A variable speed drive using a switched-reluctance motor permits a simpler and cheaper inverter than a PWM inverter for an induction motor. The various inverter circuit options are considered for singlewinding and bifilar-wound motors, noting the advantages of the bifilar 4-phase arrangement from the inverter's viewpoint. The inverter design process for a traction drive with a 3:1 constant power range is explained, followed by the calculation of main and commutation component ratings. Experimental results are given for chopping and for two single-pulse speeds. The control electronics are briefly described.

Motor with redundant windings

Abstract: An electric motor is wound with redundant sets of windings which are energized by independent electric circuits to enable operation of the motor even in the presence of a failure of a winding and a failure of an energization circuit. The motor may be of the permanent magnet form with electronic switching of the winding currents in lieu of switching via a commutator, known as a brushless DC motor, in which case separate sensing devices, such as Hall effect devices, are employed with each winding set and energization circuit for sensing the relative position between the moving and stationary members of the motor. The sets of windings, when placed on the stator, are physically spaced apart so as to minimize magnetic coupling therebetween.

Induction Motor Efficiency Test Methods

Abstract: Electric motor drives are significant to the overall energy requirements of the country and the world. The majority of these electric motors are squirrel cage induction motors, and it is to the efficiency testing of these motors that this paper is directed. It is essential that motor efficiencies be determined accurately to allow true comparisons to be made between alternate offerings and to assess correctly the motor's share of system energy consumption. IEEE Standard 112, the recognized test procedure in the United States, has recently been revised. This paper presents the revised methods and compares this Test Procedure with IEC 34-2 and JEC-37. Each of these specifications includes a variety of basic methods for determining efficiency based on motor size and availability of test equipment. The National Electrical Manufacturers' Association has recommended the use of IEEE Standard 112, Method B for ac motors of 1-125 hp. Ranking of different methods in order of desirability and practicality of use is presented.

Magnetic Field Modeling of Permanent Magnet Type Electronically Operated Synchronous Machines Using Finite Elements

Abstract: The finite element method is applied to the analysis of electronically operated permanent magnet type synchronous machines. In this class of machines, the armature MMF is a discretely forward stepping one of high harmonic content. The discretely stepping MMF is accounted for by a series of finite element field solutions as the rotor moves throughout one complete cycle of the ac armature current. Because of the discretely forward travelling MMF, a series of finite element grids depicting the rotor at various equally spaced locations, covering its movement during one cycle of the armature current, is required. This is accomplished by means of an automated algorithm for generation of the required finite elemennt grids. This allows one to match any stator grid to any rotor grid for any given displacement between the two grids. This matching is done in the air gap region by fitting it with a suitable row of triangular elements. In addition, a permanent magnet model is developed based upon the magnet geometry and material properties. This method was applied to the analysis of a 15 hp samarium cobalt machine at both rated and no load conditions. The calculated results were in excellent agreement with search coil measurements at both of these operating conditions. These solutions were then used to determine the midgap EMF waveforms. The calculated midgap EMF was in excellent agreement with an oscillogram of the actual EMF in both waveshape and magnitude.

Pulse width modulation inverter with battery charger

Abstract: An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin θ, where θ is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120° at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a "flyback" DC-DC converter circuit for recharging the battery.

Start control arrangement for split phase induction motor

Abstract: A control arrangement for a reversible alternating current split phase induction motor of the type having a start winding electrically connected in parallel with a run winding, which controls the duty cycle of current in the start winding to selectively initiate rotation of the motor in the desired direction. In one form of the invention, a thyristor switching device is connected in series with the start winding to phase control the start winding current. An electronic controller triggers the thyristor into conduction at a first firing angle to initiate motor rotation in one direction and at a second firing angle to initiate motor rotation in the other direction. The first firing angle is less than 45° and preferably in the range of 25°-45° relative to the supply voltage signal and the second firing angle is preferably in the range of 90°-135° relative to the supply voltage signal. In another form of the invention, the control arrangement additionally includes a monitoring circuit which monitors the phase angle between line voltage and run winding current. The controller is responsive to the monitoring circuit to inhibit thyristor trigger signals to the start winding thyristor when a predetermined relationship exists between the phase angle and a reference value, thereby effectively switching the start winding out of the circuit when the motor gets up to speed.

Electric constant speed/variable speed drive/generator assembly

Abstract: The invention is an "electric" constant speed/variable speed drive/generator assembly (10), which finds use in aircraft, and in particular, in "all-electric" aircraft. The assembly (10) includes a planetary differential (20) whose output is controlled by a "make-up" induction motor (12). The induction motor (12) includes a squirrel-cage rotor (14) which is rotatable about a rotor-shaped stator (16). The assembly also includes a primary power generator (30) which includes a permanent magnet rotor (18) and an output winding (22). The rotor (18) is co-axial with and rotatable about, the outside of the rotor (14). The outer rotor (18) is driven by the planetary differential (20) in such a manner that the planet-carrier (24) is driven by the aircraft's engine, the ring-gear (26) drives the generator (30), and the sun-gear (32) is connected to the induction motor (12). Constant speed operation of the device is effective when the band-brake (34) is "off" and the induction motor (12) rotates at a speed, and in a direction, to compensate for the in-flight variations of the engine input-speeds to the planetary differential (20). When the band-brake (34) is "on," the sun-gear (32) is locked and the differential acts as a fixed ratio transmission. The result is a dual-speed range all-electric drive which enables the generator (30) to provide constant voltage/constant frequency or variable voltage/variable frequency power (proportional to engine speed).

Marine propulsion system

Abstract: A marine propulson system is described that includes a gas turbine, an alternating current generator, a fixed pitch propeller, a synchronous motor and a frequency converter. The frequency converted is connected electrically between the generator and motor during starting and reversal procedures when the motor would normally have to operate as an induction motor. Means are provided to brake the system dynamically to speeds within the capacity of the frequency converter. At speeds within the frequency converter's design capacity, the motor can be operated synchronously while it is running at a speed below the minimum operating speed of the turbine and generator.

High-field self-starting permanent-magnet synchronous motor

Abstract: A number of configurations of self-starting permanent-magnet synchronous motor have been developed in recent years. This paper describes a form of motor having a high efficiency/power-factor product. Use can be made of ferrite, Alnico or rare-earth magnets. The machine is particularly suitable for variable-speed drives involving the combination of an inverter and one or more synchronous motors, where the speed of rotation needs to be accurately determed. The characteristics of the machine are discussed results indicating the performance are presented.

Power factor controller

Abstract: A power factor controller for an AC induction motor which controls the input power to the motor commensurate with the loading on the motor so as to improve efficiency. The circuit provides a signal representative of the phase difference between the current through the motor and the voltage across it. The phase difference varies with motor loading and accordingly is utilized to control the input power to the motor. The improvement in efficiency is displayed in terms of the percent savings provided by the controller. The circuit provides an immediate response to initial energization of the motor to enable the motor to reach full speed in minimum time.

System for indirectly sensing flux in an induction motor

Abstract: Flux saturation in a current-excited induction motor is detected by sensing an accompanying increase in the level of the third harmonic in the waveform of the voltage across the stator windings. The level of the third harmonic relative to a fixed reference represents flux error. Nulling the flux error with a servo loop facilitates torque control by maintaining constant flux.

Motor power factor controller with a reduced voltage starter

Abstract: A power factor type motor controller in which the conventional power factor constant voltage command signal is replaced during a starting interval with a graduated control voltage. The present invention adds to the three-phase system of pending application Ser. No. 199,765, filed Oct. 23, 1980, means for modifying the operation of the system for a motor start-up interval of 5 to 30 seconds. The modification is that of providing via ramp generator 174 an initial ramp-like signal which replaces a constant power factor signal supplied by potentiometer 70. The ramp-like signal is applied to terminal 40 where it is summed with an operating power factor signal from phase detectors 32, 34, and 36 to thereby obtain a control signal for ultimately controlling SCR devices 12, 14, and 16 to effect a gradual turn-on of motor 10. The significant difference of the present invention over prior art is that the SCR devices are turned on at an advancing rate with time responsive to the combination signal described rather than simply a function of a ramp-like signal alone. The added signal, the operating power factor signal, enables the production of a control signal which effectively eliminates a prior problem with many motor starting circuits, which is that of accompanying motor instabilities.

Transient Analysis of Three-Phase SCR Controlled Induction Motors

Abstract: The problem of simulating the transient performance of thyristor controlled three-phase induction motors is discussed. A method of solution by digital simulation using phase variables has been developed and is presented. The method enables transient current, speed, and electromagnetic torque patterns to be predicted for run-up conditions and conditions of operating mode transition. Application of the method is illustrated and sample results are presented and discussed.

Apparatus and methods for controlling induction motors

Abstract: When induction motors are lightly loaded, their powerfac- tors and efficiency are poor but in the arrangement power factor is controlled regardless of load. An induction motor (10) is connected by way of a triac (12) to a supply (11). The voltage across the triac (12) is monitored by a comparator (21) for voltage steps which correspond to current turn-off and a signal is developed at the output of an amplifier (19), which represents error from required phase lag. A comparator (17) and trigger pulse generator (16) trigger the triac (12) in accordance with the error. An override circuit (31) overrides the control system during starting. A number of further induction motors (28, 29) may be connected in parallel with the motor (10). Additional circuits deal with problems arising when a three-phase induction motor is connected by three wires only.

Composite control for soft start and dynamic braking of a three-phase induction motor

Abstract: A control circuit for a three phase induction motor includes a voltage controller having a silicon controlled rectifier in each of a first, second and third supply line connected to the motor. The control circuit further includes a first, second and third phase control means for controlling the firing angles of the respective silicon controlled rectifiers, a circuit for providing a positive ramp signal, and a circuit for providing a constant level signal. A starter circuit includes a "run" push button and a "brake" push button. The depressing of the "run" push button connects a three phase power supply to the supply lines of the voltage controller and causes the positive ramp signal to be applied to the first, second and third control means to control the firing angles of the silicon controlled rectifiers to provide a soft start for the motor. The subsequent depressing of the "brake" push button renders the second and third phase control means inoperable thus terminating the running of the motor and applies the constant level signal in place of the positive ramp signal to the first phase control means to control the firing angle of the silicon controlled rectifier in the first supply line to thereby provide a D.C. current for braking the cruising motor.

Subsynchronous resonance of single-cage induction motors

Abstract: This paper presents the results of an investigation into the subsynchronous resonance (SSR) instability of a single-cage induction motor supplied by a series capacitor compensated feeder. A great deal of insight into the mechanism of subsynchronous resonance instability is obtained from a simple equivalent circuit analysis and the discrete Fourier transforms (DFTs) of some of the transient waveforms.

Steady-State Analysis of a Permanent Magnet Synchronous Motor Drive with Current Source Inverter

Abstract: A steady-state analysis of a permanent magnet (PM) synchronous motor drive with a voltage-source inverter (VSI) is presented. The torque-speed profile required of the drive is a constant torque region from zero to base speed and a constant power region above base speed. Assuming position feedback control from a shaft-position sensor, optimum strategies are obtained for the two regions of the torque-speed profile. Using these optimum strategies, performance curves of the drive are predicted and experimentally verified. The harmonic distortion in the motor is strongly dependent on the presence and configuration of dampers in the motor. An expression is obtained for the equivalent inductance seen by the harmonics for different damper configurations. A Fourier series approach is used to predict the line current waveforms. Since dampers are not otherwise essential to the operation of this type of drive and since the line current without dampers is nearly sinusoidal, it is concluded that it is advantageous not to have dampers in the motor.

Test Results on a Low Loss Amorphous Iron Induction Motor

Abstract: The extremely low magnetic losses of amorphous metals motivated construction and testing of an induction motor stator using this material. A 1/3 horsepower, two-pole, 230 V, three-phase stator was built using the conventional approach of stacked laminations. Because of dimensional limitations of available material, the core was constructed with six 60°segments in each layer. Two comparison stators were made using 0.46 mm common iron and 0.36 mm M22 silicon iron core laminations.

Methods and apparatuses for determining the temperature of an asynchronous motor

Abstract: The winding temperature of an asynchronous motor is determined for control as regards overheating, in that a value representing the prevailing motor resistance is calculated on the basis of the amplitude of the voltage (2) impressed on the motor, the amplitude of the motor current (1), the phase angle (8) between the voltage and the current, as well as the slip (3), derived from overtones in the current flowing in the input lines to the motor. The resistance value is converted (15) to a corresponding temperature value which is used for updating a winding temperature value produced in parallel on the basis of the difference between the dissipated power and the cooling loss power, when the slip lies within predetermined limits.

Self generative variable speed induction motor drive

Abstract: An inverter controls an induction motor in response to signals from a power factor control circuit. The power factor control circuit receives signals related to motor terminal voltages and multiplexes them to a comparator. The inverter and multiplexor are sequenced each time the comparator input reaches a reference level. The frequency of the inverter is thus self generated. The power factor of the system can be controlled to implement a variety of control strategies.

Polyphase motor drive system with balanced modulation

Abstract: Sinusoidal excitation currents are supplied to the three terminals of a "wye" or "delta" connected three phase motor by an improved multiphase motor energizing drive system. For each terminal associated with a different phase, an individual feedback signal representing the current flowing into that respective terminal is sensed and subtracted from its corresponding controllable sine wave reference command to produce a current error signal for each terminal. The error signal for each of these currents is preferably converted to a two-state signal by means of an associated pulse width modulator. The modulator outputs are used to control power semiconductor switches which connect the corresponding motor terminal to either the positive or negative dc voltage. In the preferred system, for one of the terminals, the associated current feedback loop and reference command are omitted, and the associated pulse width modulator is driven by the inverted sum of the error signals from the other two phases. The result is inherently balanced multiphase excitation currents into the motor terminals.

Half-pitch capacitor induction motor

Abstract: A balanced, half-pitch capacitor induction motor having a stator core member (14) with equally spaced teeth (16) equal in number to twice the number of motor poles and with the inner ends of the teeth (16) having equal angular extent, and a squirrel cage rotor member (22) The main field winding (34) comprises serially connected coils (34-1, 34-3, 34-5, 34-7) equal in number to the number of motor poles respectively embracing alternate, consecutive ones (16-1, 16-3, 16-5, 16-7) of the teeth (16) and being adapted to be connected across a single phase source (36) of alternating current An auxiliary field winding (38) comprises serially connected (38-2, 38-4, 38-6, 38-8) embracing consecutive teeth (16-2, 4, 6, 8) intermediate the teeth (16-1, 3, 5, 7) having the main winding coils (34) thereon, the auxiliary winding coils (38) being serially connected with a phase-displacing capacitor (40) across the serially connected main winding coils (34) The main and auxiliary windings (34,38) have equal ampere turns and equal pitch thereby providing a balanced, half-pitch, two phase motor winding The rotor member (22) has its squirrel cage bars (32) spiraled by one-tenth of a full turn, ie, two pole pitches of the 5th harmonic of 36° to eliminate the fifth harmonic in the speed torque curve

Current Order Coordination in Miltiterminal DC Systems

Abstract: This paper reviews certain vital control functions central to the practical implementation of parallel multiterminal do (MTDC) systems. Particularly, the requirements for coordination of current orders during different operating conditions of MTDC systems are discussed. Two new techniques of current order coordination are described. The two techniques are referred to in this paper as the Modulation Coordination and the Decentralized Current Reference Balancer (DCRB).

Motor power control circuit for A.C. induction motors

Abstract: A motor power control of the type which functions by controlling the power factor wherein one of the parameters of power factor current "on" time is determined by the "on" time of a triac through which current is supplied to the motor, and wherein, by means of a positive feedback circuit, a wider range of control is effected.

DC Brushless motor and its driving control system

Abstract: A direct current brushless motor is structured by fixing a ring-shape magnetic rotor to a rotor shaft in one piece by way of the magnet yoke, and by arranging the position of the insulating plate on which the magnetic induction elements for detecting the magnetic field of the rotor magnet, stator windings and the rotor yoke are installed, so as to have the rotor magnet oppose the stator windings across an air gap. The stator windings are composed of delta connection wirings and the windings of each phase are placed on a concentric circle having the rotor shaft at its center and in a position dividing the said circle in equiangular areas. The magnetic induction elements are provided in three with the first, second and third elements being respectively fixed at the positions where their respective phases are advanced by π/6 radian in the electric angle from the respective centers of the first phase, second phase and third phase coils. These magnetic induction elements pick up only the plus-side output signals and let the current flow respectively to the aforesaid three-phased stator windings through an amplifier, whereby they form a driving circuit for driving said rotor shaft.

Analysis of Ventilation and Cooling System for Induction Motors

Abstract: A new analytical method for a ventilation and cooling system of induction motors to provide precise results in a short period of time by a simple calculation is developed.

Multiple Restriking Voltage Effect in a Vacuum Circuit Breaker on Motor Insulation

Abstract: It has been feared that steep front transient voltage, occurring when switching off a motor, would damage induction motor insulation. In order to investigate the switching surge effect for motor insulation, switching surge waveforms, in the order of several hundred ns at the restriking voltage time, were obtained from experiments and simulations as parameters of cable length, stray inductance and capacitance around the vacuum circuit breaker.

Polyphase power factor controller

Abstract: A power factor controller for an AC induction motor which includes a control circuit adapted to be electrically connected in series with the motor for controlling the voltage applied to the motor. A sensing circuit provides phase lag signals corresponding to the difference in phase between the current through the motor and voltage across the motor. An oscillation circuit produces a cyclical output whose frequency is variable and is dependent on the value of the phase lag signal. A counter receives the cyclical output and produces a control signal corresponding to a predetermined cycle count of the cyclical output so that the duration of the control signal is dependent upon the phase difference. The control signal is applied to the control device for controlling the conduction angle of the voltage applied to the motor to thereby provide power to the motor in accordance with motor loading. Additionally, both soft start and hard start circuits are included and current limit or current trip circuits are provided for starting and running of the motor. A polyphase power factor controller is described and an additional phase loss lockout protection circuit is included.

Means and method of sensing motor rotation speed from stray escaping flux

Abstract: For isolating dynamic rotational signal components from a dominating line frequency component in the stray magnetic fields escaping from the motor, a pick-up probe for instrumentation analyzing the motor characteristics is provided with a feedback winding and feedback circuit resonant therewith over a band including a harmonic of the normal motor rotational speed, i.e. full rated load speed. Thus, sensing of a-c induction motor conditions can occur with a single uncritically spaced external probe that needs no motor mechanical, photo or electrical additions or modifications. No access need be had to rotating motor shafts or driven mechanisms. Thus for the first time instrumentation is made independent of installation of accessories by skilled technicians in existing locations for monitoring motor characteristics. Nor are special motors with special wiring, coils, rotating elements or accessories necessary to couple monitors. Appropriate circuit analyzers determine from derived pulses representative of dynamic instantaneous rotation speed of the motor, such characteristics as slip, r.p.m., load, etc.