Showing papers on "Induction motor published in 1974"

Induction motor control system

Abstract: An improved induction motor control system. Single-phase and three-phase AC induction motors are controlled in accordance with the equation y=m=x+b, where y is the phase angle, m is the slop, x is the firing delay and b is the offset. Subsequently, the firing delay is increased by predetermined amounts, the behavior of the phase angle is evaluated for several cycles, and the motor is controlled based on the results of the evaluation, thereby minimizing energy consumption.

Electronically commutated motor and method of making same

Abstract: A brushless DC motor is constructed with photosensitive devices for detecting rotor shaft position. Arcuate permanent magnets on the rotor provide a DC flux field while distributed stator windings, each spanning a fixed number of slots in the armature assembly, provide mutually perpendicular magnetic fields. A logic circuit comprising NOR gates and transistor switches and drivers activated in response to signals from the shaft position sensors are utilized to control current switching in the stator windings of the motor. A light interrupting shutter mounted to the rotor cooperates with the light sensitive devices which are mounted to a supporting bracket fixed to the stator assembly in a manner to selectively preset advancement of commutation of the stator windings.

A Novel Approach to Induction Motor Transfer Functions

Abstract: The scope of static ac drives is increasing rapidly, and with this increase has evolved the need to devise control strategies for a variety of new applications. Purely analytical approaches to design of control systems for ac drives are hindered by the highly coupled nature of the ac induction motor equations which, in the past, necessitated lengthy manual derivations of transfer functions. This paper presents an alternative approach using a state variable formulation. The equations are arranged in a form such that the entire derivation procedure can be relegated to a digital computer. Transfer function poles, zeros, and gain for any practical input-output pair of variables can be rapidly obtained.

Energy absorbing unit for physical exercising devices

Abstract: An energy absorbing unit for physical exercising devices is arranged as an asynchronous motor the stator of which has windings to be connected to an AC supply and cooperates with the rotor of ferromagnetic material having a circular circumference, and an input shaft and an epicyclic gearing arranged inside the rotor circumference operatively connecting the input shaft to the rotor with the input shaft adapted to be driven by the training person, in order to generate an electromagnetic motive force on the rotor to tend to drive it in the direction opposing movement of the shaft by the training person and thereby act as a braking force on the shaft independently of the movement thereof.

Vernier reluctance motor

Abstract: Reluctance motors depend for their operation on the existence of alternate zones of higher and lower permeance between stator and rotor round the periphery. In the usual form of reluctance motor this is provided by salient poles on the rotor. In the vernier form of reluctance motor it results from both stator and rotor having teeth, separated by open slots, with the number of teeth on the stator slightly different from the number on the rotor. Then there are zones where stator teeth are most nearly opposite to rotor teeth and the permeance is larger, alternating with zones where the stator teeth are opposite to rotor slots and the permeance is smaller. Such motors run `synchronously', with the rotor speed a certain fraction of the speed of the axis of the applied m.m.f. The torque obtainable depends in a rather complicated manner on the proportions of the dimensions of teeth, slots and air gap and on the waveform of m.m.f. Various relationships giving peripheral force and output are derived, and the conditions are found by which the output can be maximised. The possible output coefficient so estimated is compared with the output coefficients of various other forms of machine. It appears from this comparison that the best output coefficient possible is intermediate between the coefficients for a d.c. motor and for an induction motor. Any suggestion that the vernier construction might provide an exceptionally large output coefficient is thus disproved.

Flux control system for controlled induction motors

Abstract: An induction motor, supplied by a static converter power supply which is independently adjustable as to frequency and voltage, is voltage controlled so as to keep the flux at an optimum constant level while the frequency is varied and load conditions change substantially. Flux regulation is obtained from a signal processor providing a synthesized representation of the square of the magnetizing current multiplied by the frequency derived from the analog sensing of the supplied voltages and currents. In a negative feedback loop the synthesized signal is compared to a reference signal which is proportional to frequency, and the voltage is controlled therefrom, whereby the magnetizing current developed on the stator of the motor remains constant when frequency varies.

Dynamic Equibalents of Asynchronous Motor Loads in System Stability Studies

Abstract: The dynamic behavior of complex asynchronous motor loads has been investigated by means of a digital computer program based on general equations for induction machines. The paper is devoted to load-voltage relationships. Load-frequency characteristics are not discussed in detail.

Solid state motor starting control

Abstract: An improved solid state motor starting switch is disclosed, which switch is adaptable to single-phase induction motors of the split-phase, capacitor-start, or capacitor-start capacitor-run type, the switch circuit utilizing bidirectional semiconductor devices and a running winding current sensitive control device such as a bias resistor, inductor or transformer, for operating the semiconductor device, typically one or more triacs, to ON and OFF states, respectively, during motor starting and motor running conditions. Two rectifier or zener diodes, parallel connected back-to-back, are disposed in series connection in the gate circuit of the semiconductor switch such that the control device develops a control voltage in excess of the diode forward voltage during motor starting. During normal running, the control voltage from the control device falls below the diode forward voltage drop in the PN junction region such that leakage current is very small in order to reduce the triac gate voltage to a correspondingly small value during motor running conditions.

Method and apparatus for controlling the speed of induction motors

Abstract: In a method and apparatus for controlling the speed of an induction motor energized from a source of variable frequency, e.g. a controllable inverter, a control signal which is a function of the primary current of the induction motor is produced, a predetermined slip frequency pattern signal is generated in accordance with the control signal, and the source is controlled in accordance with the slip frequency pattern signal for controlling the operating frequency. By suitably determining the shape of the slip frequency pattern signal it is possible to operate the induction motor with either one of normal induction motor characteristic, DC series motor characteristic, DC shunt motor characteristic, DC weak field motor characteristic and DC compound motor characteristic, and to operate the induction motor for smooth and continuous power regeneration.

Modeling of DC Motors for Control Applications

Abstract: Three different mathematical models of an armature-controlled dc motor are considered: (i) a precise nonlinear model, (ii) a piecewise linear model, and (iii) a second-order linear model. Experimental results are presented comparing the various models, and a range of applications for each is suggested.

A Comparative Study of Symmetrical Three-Phase Circuits for Phase-Controlled AC Motor Drives

Abstract: The speed of an induction motor in certain types of drives can be adjusted by phase control of the applied voltage. Three pairs of inverse-parallel thyristors are required for three-phase bipolar symmetry, but several different arrangements of the thyristors and motor windings are possible. A direct series connection of thyristors and windings in each phase can be made; the three phases can then be connected in delta, wye, or wye with neutral return. Alternatively, a delta connection of thyristor modules can be inserted in the opened neutral junction of wye-connected windings. Representation of the motor as a counter EMF in series with leakage reactance allows a simplified analysis of the current waveforms in terms of the thyristor conduction angle. With a given fundamental current, the current harmonics in the motor windings and in the supply lines for each of the circuits can then be compared. The results are equally applicable to thyristor-controlled inductive loads such as may be used for reactive power adjustment.

A.C. motor starting system

Abstract: A single-phase induction motor is provided with a simple capacitor-start control system. A precision current detector (reed relay) is used in the main winding circuit to fire a bidirectional thyristor and precisely control the starting and stopping points of energization of the start winding to cause the motor to accelerate to the desired speed. Although this small reed relay is a fast acting device that picks up on the leading side and drops out on the trailing side of each current half-cycle, chopping up of the current wave is avoided by the combination used. Thus, in view of the nearly 90 degree phase-shift between the main winding and start winding currents, the reed relay, with its dropout point being lower in current value than its pickup point on each half-cycle due to the inherent differential in its magnetic characteristics, applies a wide firing pulse to the thyristor at the most desirable time, that is, it widely overlaps the point where the start winding current passes through zero. Thus, the thyristor is force-fired at the beginning of each half-cycle for symmetrical triggering. And since the thyristor conducts for the remainder of each half-cycle, this start winding thyristor affords full-cycle conduction even though the reed switch itself is not closed throughout each half-cycle of main winding current thereby avoiding chopping up of the start winding current wave. In addition, this combination avoids hysteresis in that the current value at which the reed relay starts picking up on consecutive half-cycles and the lower current value at which it stops picking up on consecutive half-cycles are very close to one another thereby affording accurate control of the start winding.

Regenerative braking circuit

Abstract: An inverter device which delivers a-c power to an induction motor during motoring and receives power therefrom during regenerative braking has a current commutating capability which varies with the input voltage. During the regenerative braking mode of operation, the input voltage is increased by inserting an impedance in series between the d-c power source and the inverter, thereby increasing the input voltage level beyond that of the d-c power source. The resulting increased current commutation capacity and increased voltage provides for greater power generation without increasing the size of the inverter device. During motoring operation the impedance is removed to provide for the free flow of current to the inverter.

Control system for induction motors

Abstract: Both analog and logic elements are utilized in a control system for an induction motor. A TRIAC delivers power to the run winding of the motor. In response to a control signal which represents the magnetic flux in the air gap, a regulator initiates a control pulse timed after a zero crossing of the alternating current so as to be proportional to the control signal. The control pulse governs operation of trigger circuitry which fires the gate of the TRIAC at a time when the latter is non-conducting. Temperature-responsive and threshold circuits are combined to inhibit application of the firing pulse under a condition of motor overheating or when its rotor is stalled. In addition, a signal representative of motor speed is utilized in threshold circuitry to develop additional firing pulses that are used to gate a second TRIAC which controls the delivery of power to the start winding of the motor. As an adjunct to proportional control of motor operation, the inclusion of supplemental logic components permits the motor alternately to be stopped and started, with the motor reversing direction upon each successive new start, to effect reversal of the motor in response to a stall signal when the motor is operating in one direction and to deenergize the motor upon the occurrence of a stall signal when operating in the other direction. This extended feature is particularly suitable for use in connection with a garage door operator.

System for operating a self-propelled track bound vehicle with a linear synchronous motor

Abstract: A circuit arrangement for the operation of a track-bound selfpropelled (or propulsion) vehicle driven by a synchronous linear motor with the stator of the linear motor installed along the roadway as a traveling field winding, and its exciter winding on the vehicle as a co-moving translator, in which the stator of the synchronous linear motor is supplied with variable voltage and frequency by a stationary, controlled static converter timed as a function of the position of the translator relative to the stator with the position calculated by a computing circuit using values of the voltage and current which exist at the feeding point of the converter into the stator.

High efficiency induction motor with multi-cage rotor

Abstract: Fractional horsepower induction motors having a fixed number of poles (and, accordingly, a single no load synchronous speed) that are particularly adapted for multi-speed operation when driving a fan load by changing the field strength of the main winding. Induction motors of N fundamental poles have squirrel cage rotor having a plurality of interrelated conductor bars and end rings that are arranged so that multiple sets of the rotor bars establish a predetermined number of separately identifiable cage sets such that the fundamental pole structure of the stator field is coupled with the rotor and such that the third harmonic of the stator field is not coupled with the rotor. The rotor slot number and total number of separately identifiable cage sets are selected so that a cage set pattern is provided that has two-thirds of a fundamental pole pitch. In addition, the number of rotor cage end rings at one end times the number of rotor cage end rings at the other end is greater than or equal to the number of different cage types.

Electronic commutation system having motor stator windings in push-pull

Abstract: An n-phase electronically commutated motor has a stator with n angularly displaced phase windings, each of which comprises a pair of power windings, and each power winding is connected in series with a transistor power switch across an electric power source so that the power windings of each phase generate magnetic fluxes in opposite directions and operate in push-pull. A capacitive rotor sensor coupled to the motor rotor derives n-phase square wave rotor position signals displaced 360/n degrees apart at a frequency proportional to rotor speed and n sets of logic gates receive the rotor position signals and control the conduction interval of the power transistors. The logic gates are opened during rotor position signals which energize the power switches in a sequence that generates a rotating magnetic field within the stator.

Rotor for squirrel-cage induction motor

Abstract: A rotor for a squirrel-cage induction motor in which a thermosetting resin consisting essentially of a polyfunctional epoxy compound and a polyfunctional isocyanate compound and containing a catalyst which forms an isocyanurate ring and an oxazolidone ring has been impregnated between the slot of a rotor iron core and a rotor bar to bond the rotor bar to the slot. The rotor shows excellent adhesive strength between the slot and the rotor bar particularly at high temperatures and thereby can prevent the vibration produced between the slot and the rotor bar.

Closed-loop, precision-stop induction motor control circuit

Abstract: An induction motor deceleration control circuit capable of activating apparatus peripheral to the induction motor when the motor output shaft is at a predetermined speed and position, and then stopping the output shaft precisely at a predetermined position, all in a rapid one-step operation, is illustrated herein. The control circuit includes apparatus for providing an AC drive signal to the induction motor, a control for reducing the frequency of that AC drive signal in order to reduce the operating speed of the motor, a feedback loop for identifying the speed and position of the motor output shaft, and a brake control responsive to the feedback loop for converting the AC drive signal to a DC braking signal when the motor shaft slows to a predetermined speed and reaches a predetermined position. The controlled application of a braking signal in accordance with motor output shaft speed and position ensures that the shaft will only rotate through a known angle after application of the braking force and thus stop precisely at a predetermined distance. The control circuit also includes apparatus responsive to the feedback circuit for activating apparatus peripheral to the induction motor just before the induction motor is stopped, when the motor output shaft has a predetermined speed and position.

Novel Simulation of Cage Windings Based on Mesh Circuit Model

Abstract: Representing the cage winding of a polyphase induction motor as a set of mesh circuits results in the rotor being faithfully modelled by a simple symmetric matrix. The application of a new transform reduces the model to its two-axis equivalent with novel expressions for impedance, which avoid many of the complications of other methods of cage winding simulation. The derived impedance expressions are rigourously applicable to machines which are unbalanced to the extent of having non-integral numbers of rotor bars per pole-pair. No assumptions are required about the magnitudes of rotor currents and all harmonics can be included.

A linear synchronous motor for high-speed ground transport

Abstract: This paper describes a linear synchronous motor which has been designed to propel a 500 km/hr electrodynamically-levitated vehicle. Superconducting magnets on the vehicle interact with an aluminum-cable winding built into the guideway. Following a description of the motor, a coupled-circuit model is derived and used to optimize the winding Configuration and to predict the performance of the motor. An inverter which acts as a controllable current source is used with the motor.

DC/AC motor drive for a downhole acoustic transmitter in a logging-while-drilling system

Abstract: In a system for logging while drilling, a downhole turbine is rotated by the hydraulic power in the circulating drilling fluid to provide mechanical power that is converted to regulated DC power. The DC power is converted to two-phase AC power by a DC/AC motor drive. The frequency of the two-phase AC power output of the DC/AC motor drive is modulated by the output of a downhole transducer which monitors a selected downhole condition. A two-phase AC induction motor is driven by the DC/AC motor drive at a speed which changes with the frequency modulation of the two-phase AC power. The induction motor drives an acoustic transmitter which interrupts the circulating drilling fluid to produce an acoustic wave in the drilling fluid that is frequency modulated in response to changes in the condition being measured by the downhole transducer.

Protector system for an electric motor

Abstract: This disclosure deals with a protection circuit for an electric motor, the motor being connected by power lines to a power supply. A thermal protector switch is connected in at least one of the lines and is mounted closely adjacent at least one of the windings of the motor, and a main contactor is connected in the lines to control the flow of power to the motor. The circuit includes means for responding to the opening of the protector switch by sensing the absence of current flow in the power line to which it is connected, and for actuating the main contactor to open the power lines. The protection circuit further includes means for preventing automatic reapplication of power to the motor even though the protector switch is automatically resettable, thereby requiring manual resetting of the circuit. In the case of a three phase motor, the circuit enables the use of a single protector switch thereby avoiding problems due to random resetting of plural protection switches.

Thyristor control system

Abstract: An induction motor is coupled to a three-phase AC source through thyristors controlled by a digital control circuit. An adjustable device gates a selected number of clock pulses to a control counter. As one of the AC phases goes positive, the control counter is incremented or decremented by clock pulses until reaching a predetermined count, which causes a trigger means to generate a trigger pulse and fire a thyristor. The trigger pulse also gates clock pulses to a second control counter which counts to 120° and 240° representing numbers in order to fire the other thyristors. In a speed feedback embodiment, rotation of the motor generates a motor feedback signal which is compared with a desired speed signal to adjust the count of an up/down counter, the contents of which are loaded into the control counter.

System for controlling operation of the rotating anode of an x-ray tube

Abstract: A closed loop system is disclosed for monitoring and regulating the power applied to the stator of an induction motor for controlling the operation of the rotating anode of an X-ray tube in order to insure acceleration of the rotor to a selected speed of rotation, to maintain the selected speed of rotation, and to provide a braking voltage to the rotor as desired. The system provides direct inter-related operation of an anode rotor, an anode rotor rotation sensing detector, and an X-ray generator.

Method and control system for improved stability of an induction motor via independent voltage, synchronous frequency, and slip frequency control at an operating point

Abstract: The invention relates to a method and control system to improve stability of an induction motor by means of regulating, independently, the voltage, the synchronous frequency applied to the motor and the slip frequency of the motor. The system applies a voltage to the motor at a synchronous frequency and at a magnitude derived from an error signal indicative of the differences between a desired rotor speed or position and the true rotor speed or position. The synchronous frequency as determined by this control system is the sum of a desired slip frequency and a desired rotor frequency.

Electric hoist control and braking system

Abstract: The invention relates to control and braking systems for apparatus driven by single and polyphase alternating current induction motors. The system prevents destructive and dangerous overspeeding where the nature of the driven load is such that it can furnish sufficient torque to overdrive the apparatus in any one of several potential failure modes. A capacitor selected according to this invention is permanently connected across the motor winding such as to cause the drive motor to automatically develop retarding torque in the absence of power supplied thereto sufficient to restrict the overdrive speed to a value not appreciably exceeding the normal operating speed. The system also incorporates drive motors specifically designed with a predetermined value of starting torque appreciably less than that conventionally applied to similar apparatus for the specific purpose of limiting the load handling capability of the apparatus, thus preventing dangerous overloading. Numerous related benefits are attained through the aforementioned features, including improved controllability, improved holding brake life, and more reliable arresting of motion at limits of safe travel.

Direct current and synchronous motor system

Abstract: A motor control system in which direct current is sequentially applied to portions of the motor stator windings in response to rotor position signals generated by Hall effect devices until the rotor has reached a desired angular velocity corresponding to the frequency of a source of reference pulses, at which time the portions of the stator windings are driven in a synchronous manner by pulses having a fixed duration and the same frequency as the reference pulses. In the synchronous mode the Hall effect signals are used only in conjunction with circuitry to determine whether or not the rotor is continuing to rotate at the desired, synchronous velocity. The motor is stopped by reverse application of direct current drive to the windings in the direct current drive mode and, again, in accordance with the position signals output from the Hall effect devices. Sine and cosine drive circuitry is disclosed to enable the generation of a substantially continuously rotating magnetic field by the stator windings to allow smooth rotor rotation at very low speeds. Further circuitry is disclosed to provide a hyperbolic variation in the frequency of the reference pulses to allow utilization of the motor system in a disc recording system, whereby substantially constant tangential velocity of a portion of the disc adjacent to a transducer radially movable along the disc is realized by movement by the transducer of a wiper of a linear potentiometer included in the hyperbolic frequency generator circuit.

Control circuit for variable reluctance motor

Abstract: A control circuit for a variable reluctance motor. A solid state switching device has its output circuit connected in series with the electrical winding of the motor. Circuit means are coupled to the motor winding and to the control electrode of the solid state switching device. The circuit means senses the EMF induced in the motor winding while the motor is rotating and while the switching device output is nonconductive. The switching device output circuit is rendered conductive when the EMF attains a predetermined level. The EMF induced in the winding of the rotating motor results from residual magnetism in the magnetic circuit of the motor or from such residual magnetism in addition to a bias current supplied to the motor winding. The variable reluctance motor acts as its own position sensor.