Showing papers on "Induction motor published in 1976"

Power factor control system for AC induction motors

Abstract: A power factor control system for use with AC induction motors which samples line voltage and current through the motor and decreases power input to the motor proportional to the detected phase displacement between current and voltage to thereby provide less power to the motor, as it is less loaded.

Dynamic single-unit representation of induction motor groups

Abstract: The paper describes a method of representing a group of induction motor loads by a single-unit equivalent. The dynamic performance of the composite group following supply disturbances is examined using the single unit model. The representation employs the induction motor steady state equivalent circuit mad allows for effects of inertia and mechanical load characteristics. Experimental results are presented and compared with corresponding theoretical results using the proposed method as well as classical techniques of analysis. Sudden and gradual supply disturbances are considered, and different load torque-speed characteristics.

Dynamic brake blending for an inverter propulsion system

Abstract: The stator terminals of an adjustable speed a-c induction motor are connected to a source of d-c electric power by means of an inverter, and a system is provided for blending both dynamic and regenerative electrical braking of the motor whenever it decelerates. The brake blending system comprises a plurality of braking resistors respectively coupled by a corresponding switch in parallel with the power source. The switches are controlled by a control circuit which responds to motor terminal voltage, motor angular velocity and the difference between the commanded and actual motor torques to determine the additional current which the motor could regenerate without exceeding commanded parameters. When the additional current corresponds to that current which can be absorbed by adding an additional stage of braking resistance, the control circuit actuates a switch to add a stage of dynamic brake resistance. The control circuit also monitors the voltage of the source and removes braking resistance in steps to maintain source voltage within selected limits in order to maximize the current fed to the power source and thus maximize regenerated energy. In an alternate embodiment the control circuit determines the admittance of the source and utilizes the admittance to maintain source voltage substantially constant by removal of dynamic brake resistance in order to force more regenerative current to the source.

Variable-speed regenerative brushless electric motor and controller system

Abstract: A synchronous polyphase motor is driven and regeneratively braked by relatively high-frequency power switching circuits that cause stator currents to vary sinusoidally with rotor position so the resultant magnetic field of the stator rotates with the rotor field at a constant optimum torque angle (leading for forward torque and lagging for reverse torque). The system includes a rotor position transducer that provides signals for each motor phase which vary sinusoidally with rotor angle for synchronous control of current in the associated stator winding, circuits to extract speed and direction, polarity, and relative amplitude from said signals, means to multiply said amplitudes by a variable which commands stator current levels, servo loops (each comprised of an operational amplifier, a pulse duration modulator, switching logic, and a current sensor) that control current in each stator winding in synchronism with rotor position and in response to forward drive, brake, and reverse drive commands and the commanded current levels; plus a circuit to adapt rotor excitation to stator current and motor speed, and an interlock including means to interpose regenerative braking whenever a motor drive command is received opposite to the motor rotation.

DC electric car with auxiliary power and AC drive motor

Abstract: An electric car is provided with a DC drive motor powered by a conventional storage battery and an AC drive motor powered by the combination of an AC generator driven by an auxiliary internal combustion engine. The car may be driven by the DC motor alone, for example during short range stop and go driving, or it may be driven by the AC motor alone, for example during relatively constant speed long range driving, or it may be driven by both motors in combination when increased power is required.

Inside-out motor/alternator with high inertia smooth rotor

Abstract: A multipole homopolar inductor motor/alternator for a flywheel drive includes a rotor assembly on the outside of the stator which functions as the flywheel. Locating the excitation field winding on the stator between two stacks of stator laminations enables the rotor assembly to be operated at much higher temperatures than a wound rotor, without detrimental effect on overall efficiency. The rotor assembly is also operable at much higher speeds than would be possible if the rotor were wound, resulting in apparatus better adapted to store energy mechanically.

Polyphase induction motors

Abstract: It has been shown in chapter 1 that the polyphase induction motor can be considered as a polyphase transformer with variable frequency in the short-circuited secondary winding and an equivalent circuit can be derived per phase of the motor in the same general way as that of a transformer. It is apparent that each winding will have resistance and leakage inductance. The leakage reactance of the rotor will, however, be dependent on the frequency of the rotor current and, since the rotor frequency is Sf, the slip frequency, where S=(N S −N)/N S is the slip and f is the supply frequency, the rotor leakage reactance is given by SX2 where X2 is the standstill value of the rotor leakage reactance. Thus an equivalent circuit for the rotor can be drawn as shown in Fig. 5.1.

Balanced operation of 3-phase induction motors connected to single-phase supplies

Abstract: A 2-element static balancer, which enables 3-phase induction motors to operate more satisfactorily from singlephase supplies, is described. It is demonstrated that balanced phase voltages and currents are possible, no matter what the machine speed or phase angle, and the economic and operational advantages are briefly discussed.

Two-phase asynchronous motor

Abstract: For the purpose of providing a two-phase asynchronous motor of the kind comprising a wound stator made up of two portions spacedly disposed parallel to each other and in which the flux flowing in all the field magnets of the stator is exclusively that of their own phase and in which sufficient space is available for a comparatively large number of field magnets, the stator windings of each phase are each accommodated in one said portion of the stator only and the poles of a member movable with respect to the stator are in the form of ferromagnetic bridges, surrounded and magnetically separated with respect to each other by a short-circuit element, the arrangement being such that the magnetic circuit of adjacent stator poles is completed directly via the pole shoes of the oppositely disposed portion of the stator. The invention is applicable to both linear and rotary motors. In the case of a rotary motor, the said member defines the rotor and the said element is in the form of a short-circuit cage.

The history of induction motors in America

Abstract: This paper briefly reviews the history of the induction motor from its invention by Nicola Tesla in 1888 through the various stages of its development-the invention of the cast aluminum squirrelcage winding, improvements in magnetic steel and insulation, and the progressive reduction of the dimensions for a given horsepower rating, so that today a 100-hp motor has the same mounting dimensions as the 7.5-hp motor of 1897.

Method and apparatus for controlling variable speed, controlled current induction motor drive systems

Abstract: A new induction motor control method and system utilizes one or more electric power inverters each supplying a separate induction motor with alternating current excitation power. The respective inverters pre-ferably comprise auto-sequential commutated controlled current inverters. Direct current is supplied to each inverter in the system from a common direct current power supply preferably comprising a phase controlled rec-tifier circuit with individual current smoothing inductors connected in the direct current link to each power inverter for isolation purposes. A com-mon operator controlled power level control module is provided for con-trolling the magnitude of the output current supplied from the common phase controlled rectifier to all of the inverters in parallel. Respective motor flux sensing means are provided for each induction motor for de-riving individual feedback control signals representative of the flux de-veloped by the respective induction motors. The flux feedback signal is summed with an input command value of a flux control signal in a suitable summing circuit, and the error signal is supplied through a suitable com-pensating circuit for regulating the flux level of the respective induction motors by individually controlling the frequency of the excitation current supplied to the stator windings of the motor by its associated inverter. In a preferred embodiment the actual electro-magnetic flux produced across the induction motor stator-rotor gap is sensed and fed back to the summing circuit for control purposes. This sensed actual value of motor flux signal also is utilized to derive an actual value of torque feedback control signal that is employed in controlling the magnitude of the direct current supplied by the common phase controlled rectifier to all of the inverters in parallel. It is also preferred to employ a phase lock-loop converter as the compensating circuit in the frequency control.

Characteristics analysis of saturated shaded pole induction motors

Abstract: It is shown, particulary for shaded pole induction motors, that saturation is an important factor, and that it varies widely when slip varies from 0 to 1. The method proposed here is completely different from the former ones; it is a step by step method; all the currents and fields are determined at each time of an half cycle. Tests and computation results are given and compared.

Optimized electric motor having controlled magnetic flux density

Abstract: A motor is disclosed in which a control winding is provided to generate magnetic flux in the stator to vary the volt-second capacity of the magnetic material of the stator in accordance with varying line, load or other selected conditions. The current in the control winding can be externally controlled or may be provided by a feedback winding wound on the stator.

New Methods of Induction Motor Torque Regulation

Abstract: Two methods of induction motor torque regulation are described utilizing speed and current feedback into the frequency and amplitude channels of a pulsewidth modulated inverter. Transfer characteristics illustrating the steady-state behavior of the two configurations are presented. Transient characteristics are discussed in detail by examining the linearized system transfer functions. An analytical approach to design of a closed loop controller for a practical application is outlined. Experimental results are presented showing correlation with predicted results.

Drive circuit for induction motor used in air conditioning system of a railway vehicle

Abstract: A drive circuit for an induction motor used in an air conditioning system of a railway vehicle operable from an applied high voltage direct current, which circuit comprises a chopper circuit having its input connected to the high voltage direct current and its output connected to a three-phase variable frequency inverter circuit which, in turn, has its output connected to the induction motor. A voltage feedback is employed to control the current output of the chopper circuit and the frequency of the inverter circuit.

Triac Speed Control of Three-Phase Induction Motor with Phase-Locked Loop Regulation

Abstract: The speed control of a three-phase squirrel cage induction motor by employing triacs in the lines which operate in the normal phase control mode is described. The inherent limitation of low circuit commutated (dv/dt), which makes the triac circuit somewhat unreliable, has been overcome by suitably designing the snubber circuit. The closed-loop speed regulation of the system is then investigated by employing digital phase-locked loop scheme. Compared to the conventional method with antiparallel SCR's and analog servo, the present scheme is somewhat simpler, more economical, and extreme precision in speed control is possible. A complete model of the speed control system has been designed and experimentally evaluated in the laboratory.

Winding machines with contact roller driven by synchronous motor or asynchronous motor

Abstract: A filament winding machine having a winding spindle driven by an rpm-controllable electric drive motor, a contact roller in frictional contact with the rotating winding being formed and driven by a synchronous or an asynchronous, 3-phase electric motor and an electric control circuit responsive to deviations in the measured effective power absorption of the latter motor for maintaining a constant linear take-up velocity of the filaments onto the winding.

Field compensated motor/generator

Abstract: A rotary electric motor/generator comprising a stator assembly including a single stator having a motor energizing winding and a generator output winding carried by the stator. A rotor is provided rotatable relative to the stator assembly, and includes a rotor winding carried by said rotor. The generator output winding is interconnected with the rotor winding to compensate for rotor reaction when the motor/generator is operating as a motor.

Control system for regulating the torque and speed of an electric motor

Abstract: A control system for regulating the torque and speed of an alternating current induction motor used in the traverse drive of an overhead travelling crane comprises an SCR bank controlled by a firing circuit responsive to actuation of an operator-controlled induction master control. The control system further comprises means for deriving a torque signal indicative of instantaneous rotor torque, means for deriving a speed signal indicative of instantaneous rotor speed, and summing means for combining the torque signal, the speed signal, and a reference signal from the induction master control to provide an error signal which is used to operate the firing circuit to thereby control the power delivered by the SCR bank to the motor and ensure that motor torque is constant for the control position selected or speed is controlled up to the torque level selected. The means for deriving the torque signal comprises means for deriving a voltage signal indicative of the instantaneous line-to-neutral voltage in the motor stator winding; means for deriving a current signal indicative of the instantaneous current in one or more phase lines to the motor stator winding; and multiplying means for multiplying the voltage and current signals to provide a wattage or torque signal which is proportional to the instantaneous torque being developed by the motor. The wattage supplied to the motor minus the wattage attributable to fixed motor losses and minus the wattage attributable to variable losses in the rotor resistance is directly related to the wattage delivered as horsepower (wattage) delivered by the motor shaft. The means for deriving the speed signal measure the magnitude of the instantaneous rotor voltage by sampling during a fixed period voltage derived from the supply voltage. The voltage being sampled is the voltage at the slip resistors connected to the motor rotor. Means are provided to combine the speed signal with the torque signal only after motor speed exceeds a desired level.

Induction motor load monitor and control apparatus

Abstract: Induction motor load conditions are monitored by sensing the slip speed of the motor which is linear over a large operating range including the 100% load condition. Electronic trigger pulses are derived from motor shaft rotation to operate a one-shot waveform generator having a selected signal pulse time duration set at the 100% motor load condition to produce a 3.5 millisecond difference from the time between two trigger pulses. Thus, as the slip speed varies the signal pulse duration varies and thus becomes a monitor of the load condition. Both analog and digital embodiments are described, and utilization devices may be an analog meter display or an alarm circuit triggered by means of an intervening threshold comparison circuit. The monitoring circuits are used to sense variations of speed and indicate on a meter a scale factor of load or horsepower, etc. as related to various drive means without interconnections other than shaft speed detectors.

Two speed single phase induction motor

Abstract: A dynamoelectric machine in the form of an induction motor is provided which is capable of two speed operation with a minimum number of motor leads and a minimum number of motor windings. The motor includes a stator assembly and a rotor assembly, the stator assembly being adapted to receive the motor windings in a conventional manner. The motor windings are constructed from a plurality of coil sets, groups of which define physical poles for the motor. The windings include a first main winding, a second main winding and an auxiliary winding. The first main winding and the auxiliary winding have an equal number of physical motor poles. The second main winding has twice the number of physical motor poles as the first main winding. The first main winding and the auxiliary winding are energized to permit motor operation at a first speed. Second speed operation is obtained by energizing the second main winding, disconnecting the auxiliary winding, and reconnecting the first main winding so that it functions as an auxiliary winding for the second main winding.

Turbomolecular high-vacuum pulp

Abstract: A turbomolecular high-vacuum pump has a substantially vertically extending cylindrical casing provided with inlet and outlet pipes for gas being evacuated. The casing accommodates, in the top part thereof, a stator having vanes disposed between the rotor vanes so as to define passages for gas being evacuated. The rotor is connected to a high-speed hollow shaft extending substantially vertically. The shaft is journalled in bearings and connected to the rotor by means of a high-frequency electric drive motor. The pump incorporates means for lubricating the bearings. The stator of the high-frequency drive motor of the pump is electrically coupled to the stator of a generator of a machine-type frequency converter which has an induction drive motor. Another, low-speed shaft is journalled in the bearings in the bottom part of the pump casing coaxially with the high-speed shaft, one shaft embracing the other. The induction motor rotor and the rotor of the generator of the machine-type frequency converter are mounted on the low-speed shaft, the stators of both devices being fixed within the pump casing. Means for lubricating the bearings of both shafts is disposed at the lower end of the low-speed shaft.

High voltage induction motor without ladder insulation between motor windings and method of construction therefor

Abstract: A permanent split capacitor induction motor rated at 460 volts AC is provided with first and second main winding parts and an auxiliary winding. The motor includes a core of magnetic material having a plurality of winding receiving slots formed in it. The main and auxiliary windings are constructed from a plurality of wire turns arranged in coil sets. The auxiliary winding is placed adjacent the first main winding part in the core slots, and is electrically connected to it. The coil sets of the auxiliary winding are separated from the coil sets defining the second main winding part by the coil sets of the first main winding part. Individual wire turns are distributed in the slots of the motor and positioned so that the voltage between coil sets forming the main winding parts and the auxiliary winding can never exceed the voltage across the capacitor. Because of the low voltage between coil sets, the coil sets of the respective windings may be placed in the slots without the use of additional insulation between coil sets other than the insulative coating provided on the wire used for coil set construction.

Elevator speed control system

Abstract: The disclosed elevator speed control system accelerates an induction motor for an elevator car in accordance with a voltage dependent upon a differential signal between a command speed signal and the actual speed signal and passed through a saturation generator. The saturation generator issues a command for applying across the motor its rated voltage upon the closure of a normally open contact set disposed in it. The system includes a sensor circuit is responsive to the difference signal less than a predetermined magnitude to decrease an output from the saturation generator. Alternatively the sensor circuit may responds to a negative load on the motor exceeding a predetermined magnitude to decrease the output from the saturation generator.

Control system of an alternating-current motor

Abstract: An alternating-current motor is used as an actuator of a positioning control system. The control variable to control the torque of the motor is the load angle θ d of a synchronous motor or the slip frequency f s of an induction motor. The highest and the lowest limit values of the control variable are respectively predetermined from the characteristics between the torque and the control variable and from other design considerations. The preparatory value E for the control variable is synthesized in accordance with an equation E=G 1 (θ c -θ a )-G 2 pθ a , where θ c is the reference position, θ a is the controlled position, G 1 and G 2 are respectively amplification constants, and p denotes the differential operator d/dt. When E is within the predetermined highest and the lowest limit values of the control variable, E is used as the control variable; when E is larger than the predetermined highest limit value, the highest limit value is used as the control variable; and when E is smaller than the predetermined lowest limit value, the lowest limit value is used as the control variable. After the control variable is thus determined, the instantaneous phase angle signal is synthesized in accordance with an equation θ p =θ a + θ d or θ p =θ a + 2 πf s /p where the instantaneous electrical angular position of the rotor of the motor is also denoted by θ a . The instantaneous phase angle of the power supply to the motor is controlled with this synthesized θ p as the reference signal. The voltage amplitude V 1 of the power supply is controlled as a constrained variable to control the torque of the motor. The reference signal of the voltage amplitude V 1 is determined as a function of the frequency of the power supply, or in one embodiment for a synchronous motor, as a function of the frequency and the load angle.

Variable speed control apparatus for induction motor

Abstract: An induction motor is operated by a power supply of variable voltage and variable frequency. The voltage and frequency of the variable-voltage variable-frequency power supply is changed by a control circuit to accelerate or decelerate the induction motor. For slowly controlling the speed of the induction motor, the ratio of the output voltage to the output frequency of the variable-voltage variable-frequency power supply is maintained substantially constant. The control circuit includes a voltage correcting means which, in response to a command for sudden acceleration or deceleration of the speed of the motor, corrects the output voltage of the power supply in accordance with the acceleration or deceleration rate and the prevailing magnitude of the output frequency of the variable-voltage variable-frequency power supply.

Apparatus for controlling the rotors of synchronous motors

Abstract: A device for measuring the angular position of the rotor of a synchronous motor relative to the rotating field thereof wherein the synchronous motor is driven by a frequency generator. The synchronous motor has an optoelectronic device generating a pulse for each rotation of the rotor and applied to the stop input of a counter whose start input receives from a frequency divider connected to the frequency generator and having a dividing factor equal to the number of poles of the synchronous motor. A frequency multiplier is also connected to the frequency generator and the output of the multiplier is applied to the counting-pulse input of the counter. The count registered on the counter in the interval between start and stop pulses is thus proportional to the lag of the rotor behind the rotating field.

Computer Analysis of 3-Phase Induction Motor Operation on Rural Open-Delta Distribution Systems

Abstract: Open-delta/open-delta and open-wye/open-delta transformer banks are often used as an economic means of supplying simultaneous single-phase and 3-phase loads in rural areas. If the 3-phase load is an induction motor, the inherent voltage unbalance causes increased losses and uneven heating that may lead to motor failure. often these motors are submersible or deep well pump motors located in remote unattended areas or air conditioning motors which may not have sufficient over-design to handle the voltage unbalance. The theory analyzing the open-delta distribution system has existed for many years, however, because of the tedious and almost infinite differences in distribution topology, the problem has been neglected. The purpose in this endeavor is to present a simple general approach to the solution of the problem by utilizing existing motor and network concepts and theories. Two previously published theories are used to predict motor heating and the motor derating that is necessary to prevent insulation failure due to the unbalanced voltages. A general motor model has been developed. Motor heating and derating are obtained from the model through a generalized digital computer program.

A Three Phase Sine Wave Reference Generator For Thyrisitorised Motor Controllers

Abstract: A variable frequency, variable amplitude three-phase low frequency sine wave reference generator is discussed in this paper. The frequency and amplitude are independently capable of being varied by means of two independent dc control voltages. This reference generator is well suited for closed loop control applications such as constant frequency power supplies, constant amplitude power supplies, induction motor control requiring a finite ratio between amplitude and frequency, etc. The reversal of polarity of the dc voltage controlling the frequency reverses the phase sequence. The reference generator has been very satisfactorily used in the control of a three-phase ``subharmonic'' pulse width modulated inverter. The reference generator is also suitable for cycloconverter control.