Showing papers on "Induction motor published in 1975"

The General Theory of Alternating Current Machines: Application to Practical Problems

Abstract: 1 The Basis of the General Theory.- 1.1 The idealized machine.- 1.2 The two-winding transformer. Explanation of sign conventions and the per-unit system for electrical quantities.- 1.3 Magneto-motive force and flux in the rotating machine.- 1.4 Voltage and torque equations of the machine. The per-unit system for mechanical quantities.- 1.5 The fundamental assumptions. Saturation, harmonics, leakage.- 1.6 Calculation and measurement of parameters.- 2 The Primitive Machine.- 2.1 The equations of the cross-field commutator machine.- 2.2 Application to a simple d.c. machine.- 2.3 Equations for small changes and small oscillations.- 2.4 Sudden short-circuit of a d.c. generator.- 3 The Steady-State Phasor Diagrams of A.C. Machines.- 3.1 Representation of sinusoidal m.m.f. and flux waves by space phasors.- 3.2 The induction motor.- 3.3 The uniform air-gap synchronous machine.- 3.4 The salient-pole synchronous machine.- 3.5 Characteristic of a synchronous machine connected to an external supply.- 4 The General Equations of A.C. Machines.- 4.1 Equations in terms of phase variables.- 4.2 Transformation between various reference frames.- 4.3 Direct derivation of two-axis equations.- 4.4 Simplified equations of a synchronous machine with two damper coils.- 4.5 Equivalent circuits, operational impedances and frequency response loci.- 4.6 Summary of the equations for the synchronous machine with two damper coils.- 4.7 Modified equations with more accurate coupling between field and damper windings.- 4.8 General equations of the induction motor.- 5 Types of Problem and Methods of Solution and Computation.- 5.1 Classification of problems and methods of solution.- 5.2 Modified machine equations in terms of rotor angle ?.- 5.3 The state variable method and the state-space concept.- 5.4 Calculation of system response and stability.- 5.5 Optimization. Performance indices.- 5.6 Computational techniques for transient studies.- 6 Automatic Control of Synchronous Machines.- 6.1 General.- 6.2 Excitation control of a.c. generators.- 6.3 Quadrature field winding. The divided-winding-rotor generator.- 6.4 Speed governors.- 7 A.C. Operation of Synchronous Machines.- 7.1 Steady operation of the synchronous machine at synchronous speed.- 7.2 Starting of a synchronous motor.- 7.3 Negative-sequence reactance of a synchronous machine.- 7.4 Small changes relative to a steady state.- 7.5 Approximate methods for forced oscillations.- 7.6 Free oscillations. Steady-state stability.- 8 Synchronous Generator Short-Circuit and System Faults.- 8.1 Symmetrical short-circuit of an unloaded synchronous generator.- 8.2 The analysis of short-circuit oscillograms.- 8.3 Short-circuit of a loaded synchronous generator.- 8.4 Unsymmetrical short-circuit of a synchronous generator.- 8.5 System fault calculations.- 8.6 Sudden load changes.- 9 Synchronous Machine Problems Requiring Step-by-Step Computations.- 9.1 Transient stability.- 9.2 Swing curves of a synchronous generator connected to an infinite bus.- 9.3 Loss of synchronism of a synchronous generator. Effect on rectifier excitation systems.- 9.4 Optimization of control inputs.- 9.5 Techniques for a multi-machine system.- 10 Effects of Saturation and Eddy Currents on Machine Performance.- 10.1 General.- 10.2 Methods of allowing for saturation.- 10.3 Effect of eddy currents in the magnetic material.- 10.4 Effect of eddy currents in the rotor conductors.- 11 Induction Motor Problems.- 11.1 Application of equations in primary reference frame.- 11.2 Equations in secondary reference frame. Complex form of the equations.- 11.3 Short-circuit and fault currents due to induction motors.- 11.4 Transient stability calculations.- 12 Application to Less Common Types of Machine.- 12.1 Classification in relation to the theory.- 12.2 Application of two-axis theory.- 12.3 Application of the phase equations.- 13 Appendices.- 13.1 Representation of a.c. and transient quantities by complex numbers. The generalized phasor.- 13.2 Current and voltage transformations when power is invariant.- 13.3 Operational methods.- 13.4 The per-unit system.- References.

Variable Speed induction Motor Drives Use Electronic Slip Calculator Based on Motor Voltages and Currents

Abstract: In certain types of adjustable frequency induction motor drives, optimal control of the motor can be best implemented by using information on the motor slip frequency. Unfortunately, this generally requires the use of an electromechanical speed transducer coupled to the shaft. The presence of this transducer spoils the general characteristics of ruggedness and mechanical simplicity typical of an ac drive. This paper discusses an improved method of obtaining the slip information without the use of rotary transducers of any kind. By sensing the electrical quantities applied to the motor (voltages, currents, and phases) and by performing simple signal processing operations on the sensed quantities, an analog signal proportional to the slip level is derived and used in motor control functions.

State-Variable Steady-State Analysis of a Controlled Current Induction Motor Drive

Abstract: The exact equations defining steady-state operation of a controlled current induction motor drive system are derived by solving the system state equations in the stationary reference frame. These equations, which assume ideal current filtering, eliminate the difficulties involved in taking derivatives of discontinuous currents by defining a pair of pseudocurrent variables. Effects of saturation are included by using the slope ratio method. Electromagnetic torque and current pulsations are computed for various load conditions, and experimental confirmation of the calculated results is made. Similarities and differences to voltage controlled characteristics are presented. It is shown that normal open-loop operation occurs on the unstable side of the torque-slip characteristic necessitating the use of feedback control for stable operation.

Linear electric machines—A personal view

Abstract: The history of linear motors is a history of shape. Once having departed from the cylindrical geometry of rotating machines, a wider world of three-dimensional design becomes possible. Linear induction motors dominate the field of linear drives to the same extent as does the rotary induction machine in relation to more complicated adjustable-speed motors. It is therefore thought appropriate to devote only one section to linear motors other than induction. A fairly full treatment of electromagnetic levitation is also included together with a treatment of oscillating machines. Perhaps the most important features are the division of electrical machines into two classes which are termed "magnetic" and "electromagnetic" and the "topological explosion" which is at present taking place in linear motor design. Some linear machines are already well established on a commercial basis but the vast bulk of recent inventions still remain to be exploited.

Torque regulating induction motor system

Abstract: A torque regulating alternating current induction motor control system comprising a motor flux sensing coil arrangement mounted on the induction motor stator for sensing the actual flux produced across the rotor-stator air gap of the motor and deriving a motor flux voltage signal proportional to the actual motor flux. An integrating circuit integrates the voltage signal to obtain a feedback sensed actual motor flux signal representative of the actual air gap flux. An actual torque feedback circuit converts the actual air gap flux and stator current signal to an actual value of torque feedback control signal. A first feedback control loop is responsive to the actual torque feedback control signal and a command value of torque signal and controls the frequency of operation of a power converter supplying the induction motor. A second feedback control loop also responsive to the feedback sensed actual value of flux converts the flux signal into a (V/Hz) voltage control signal for maintaining a substantially controlled value of rotor-stator air gap flux level. The first and second feedback control loops are interconnected and coact to maintain operation of the induction motor at a controlled value of torque. The actual torque feedback circuit includes a flux signal processing circuit for deriving from the output motor flux signals respective direct and quadrature axes flux signal components and combines these signals with direct and quadrature axes motor current signal components in multiplier circuits for multiplying the quadrature axis flux signal by the direct axis motor current signal and for multipyling the direct axis flux signal by the quadrature axis motor current signal. A summing circuit sums the two products to derive an output actual value of torque developd by the induction motor in accordance with the expression T=K(ψ d i qs -ψ q i ds ). The system is designed primarily for use with a three-phase, variable voltage, variable speed, alternating current induction motor intended for traction motor drives and makes available a new and novel actual torque measuring arrangement for use in such systems.

Pulsewidth Modulated Inverter Motor Drives with Improved Modulation

Abstract: The performance of inverter drives, which use the pulsewidth modulated (PWM) technique to control motor applied voltage and frequency, are critically influenced by the choice of the modulation policy used in the control circuits. This paper deals with practical inverter drives for squirrel cage induction motors and presents some basic considerations on modulation requirements. The advantages and limitations of popular modulation methods are discussed, and an improved modulation scheme, which allows us to extend the practical speed range of PWM ac drives, is presented.

Analysis and Comparison of Two Types of Square-Wave Inverter Drives

Abstract: The application of adjustable frequency static inverters to induction motor speed control has resulted in a diversity of inverter designs. In this paper, the state-variable formulation is applied to the analysis of two widely used drive systems incorporating square-wave inverters with 180° and 120° firing logic. Measured characteristics of an actual drive system are included, and the results are compared to an analytical solution. Steady-state speed-torque curves for each inverter supplying three markedly different types in induction motors are given. Performance of the two inverter drives are compared by a thorough investigation of typical operating points.

Transistor bridge inverter motor drive having reduced harmonics

Abstract: A harmonic reduced pulse width modulation, variable speed transistor bridge inverter drive controls frequency and magnitude of stator voltage applied to an induction motor so as to maintain constant flux in the motor and permit maximum driving torque to be realized from the motor over a wide speed range. An oscillator generates a train of clock pulses whose frequency is proportional to an analog speed signal, and a three phase generator derives three phase reference waves having periods which include a predetermined number of clock pulses. A resettable volt/hertz integrator derives a train of ramp pulses which are synchronized to the clock pulses and vary in magnitude as a function of the integral of the output voltage from the bridge inverter with respect to time. The constant volt/hertz ramp signals are compared to first and second reference voltages to derive phase-displaced first and second control pulses. The fundamental output voltages of individual phases of the bridge are regulated in accordance with respective three phase reference waves, and pulse width modulating means switch the transistors in the phases of the bridge by two different width pulses whose leading edges are established by the clock pulses and whose trailing edges are respectively at the first and at the second control pulses and in such a manner that the bridge inverter applies twelve-step voltages to the motor stator windings in which the fifth and seventh harmonics are substantially eliminated and in which the voltage-to-frequency ratio is controlled to maintain constant flux in the motor.

Rotor Chopper Control for Induction Motor Drive: TRC Strategy

Abstract: A solid-state induction motor speed regulating scheme using a rotor chopper-controlled external resistor is investigated. This control scheme provides continuous and contactless variation of rotor resistance and thereby eliminates the undesirable features of the conventional rotor resistance control method. A thorough analysis of the steady-state performance of the system is presented. Both dc and ac circuit models are derived to describe the performance characteristics when the chopper operates under the time-ratio control (TRC) strategy. Effects of machine parameters on performance characteristics are studied. Theoretical results from the model are verified by comparison with experimental results. The torque?speed characteristic of this speed control system is essentially linear for a particular time ratio.

Constant torque induction motor drive system

Abstract: An ac induction motor is supplied with variable frequency and amplitude excitation voltage by a power converter. Precise regulation of torque independent of motor parameter changes is achieved by feedback control loops for maintaining at command values constant airgap flux and also the real component of stator current with respect to airgap voltage as measured by a voltage sensor. The real stator current error controls the slip frequency which adjusts to maintain constant airgap power.

Air conditioning system for a railway vehicle

Abstract: An air conditioning system for a railway vehicle operable from an applied high voltage direct current, which system includes an alternating current induction motor driving a variable speed, helical screw-type refrigerant compressor. A variable frequency AC drive circuit is provided to power the motor from the high voltage direct current. The output frequency of the drive circuit is varied according to the cooling demand of the vehicle.

Stator terminal assembly machine

Abstract: An apparatus for attaching slotted plate terminals or the like to individual wires such as the wires of a stator coil in an induction motor is disclosed. A rotatable arbor positions the stator in alignment with an insertion track and ram. A terminal is inserted by moving it along the tracks and into a cavity in an insulating housing mounted on the stator. A guide track along which an insertion ram moves a terminal also acts as a depth control for accurate positioning of the terminal.

Variable speed induction motor

Abstract: A polyphase motor of the wound rotor type has the rotor of a polyphase generator, smaller in size than said motor, mounted on the motor shaft. Polyphase voltages produced across the generator rotor are coupled to the input of an amplifier having an output power commensurate with the size of the motor and the amplifier output is connected to the windings of the motor rotor to supply the current to the motor rotor windings. The frequency of the voltage fed to the motor rotor is inversely proportional to the motor speed, and a frequency sensitive filter is provided to adjust the output of the amplifier thereby to control the motor speed and to maintain said speed at a selected predetermined value regardless of the motor load.

Electric Motor Vibration-Cause, Prevention, and Cure

Abstract: The trend of industry toward higher speed machines and longer periods between downtimes has fostered closer surveillance of those parameters that can interrupt satisfactory service. Vibration of electric motors and systems containing motors are areas identified for consideration. Electric motor vibration is discussed from the viewpoint of its causes and cures. Also covered are the important considerations in establishing purchase specifications consistent with final installation requirements.

Controlled current induction motor drive

Abstract: Improved stable four-quadrant operation of an induction motor supplied with variable amplitude and frequency stator line current by a motor controller with a constant current source converter is achieved by using several feedback control loops to control the slip frequency as well as the stator line current amplitude and frequency Speed feedback is employed with optional control of rotor speed Motor performance is optimized by indirectly regulating air gap flux to its rated value by controlling slip frequency as a function of sensed stator current Thus, torque is approximately linear with stator current

Experimental evaluation of a high speed double sided linear induction motor

Abstract: Design details and performance testing of a high speed linear induction motor and test facility are described. The motor is double sided and of sector shape with radial slots. It has 4 poles, is 3 feet in length and is loaded by reaction with an 80 inch diameter rotating disc facility. Performance testing including efficiency, power factor, thrust, and normal force and moment are reported for operation over a speed range up to 300 MPH. A breakdown of losses, including end effects, and measurements of air gap flux density over the length of the motor are also reported. A description of instrumentation, the data Acquisition system and the load loop is given. The results are expected to be used to increase the understanding of LIM behavior and design and to provide a data base for the verification of new designs and new theoretical models.

Determination of the parameters and parameter variations of a 3-phase induction motor having a current-displacement rotor

Abstract: The paper describes a method of determining the parameters and parameter variations of a 3-phase cage induction motor having a current-displacement rotor. The method is based on the use of the Newton-Raphson procedure for the solution of two nonlinear equations in two unknowns, these being the rotor resistance and leakage reactance at any particular rotor frequency.

Self-starting synchronous and stepping motor having a permanent magnet rotor

Abstract: A self-starting synchronous or stepping motor has at least two phases, a permanent magnet rotor and a stator including individually excited and inwardly facing main stator poles. The stator poles and rotor poles have a predetermined spacing of τp. The stator poles are combined in groups of alternate polarity. The groups are displaced by a predetermined angle. At least one windingless auxiliary stator pole of approximately one-half of the width of the main stator pole is provided per group in addition to the main stator poles. The total number of stator poles is at least equal to the number of rotor poles. Additional auxiliary poles may be either half-pole widths or pointed shape. Embodiments of two-phase and three-phase synchronous motors are disclosed.

Finite-width, finite-thickness, and saturation effects in solid-rotor induction machines

Abstract: A theory for the solid-rotor induction machine is developed such that the finite width and thickness of the rotor as well as its saturation are taken into account. An axial-airgap disc-type motor is considered as an example, for which an equivalent circuit is developed, terminal characteristics are computed and compared with experimental results. The validity of the theory is thus demonstrated. Although the disc motor is used as an example, the theory is applicable to single-sided linear induction motors and other solid-rotor eddy-current motors.

Electric motor having controlled magnetic flux density

Abstract: A motor is disclosed in which the stator winding of, for example, a squirrel cage induction motor, is connected in series with a capacitor so that the capacitor, together with the input voltage, causes the stator core to periodically switch from a nonsaturated to a saturated condition and vice-versa so that the flux density is maintained at a uniform high level. A second stator winding may be provided in parallel with the first stator winding and capacitor which second winding serves to provide increased starting torque and improve the overall operating characteristics of the motor. Also disclosed is an embodiment in which an inverter is employed to permit the motor to be operated from a DC source.

Digital Computer Simulation of an Adjustable-Speed Induction Motor Drive with a Cycloconverter-Type Thyristor-Commutator in the Rotor

Abstract: This paper deals with a digital computer-simulation study of a complex drive-system which incorporates a thyristor cycloconverter-type frequency-converter in the rotor circuit of a slip-ring induction motor for speed variation in the subsynchronous as well as the supersynchronous region by secondary voltage control The action of the frequency converter is analogous to that of a normal commutator in the stator-fed ac commutator motor while the circuit behavior is similar to that of a cycloconverter. A rotor-position detector is used to switch the thyristor configuration in a sequential manner to generate an output voltage having a predominant slip-frequency component. Simulation involves solution of a set of generalized performance equations of an ideal induction machine in an appropriate reference frame under the control conditions imposed by the thyristor-commutator which is simulated using simple logical and limiting statements. Differential equations are solved by the well-known Runge-Kutta numerical integration method. Initial simulation results assuming thyristors as ideal switches and neglecting source impedances show very similar characteristics to the case when a pure sine-wave slip-frequency voltage is injected to the rotor. Rigorous simulation results include the physical thyristor behavior, effect of source impedances, overlap, and logical control of the circulating currents that may occur. Simulation results are presented together with the experimental performance of the drive.

Variable speed drive for induction motor

Abstract: A variable speed drive is provided for a polyphase induction motor The motor is connected through a contactor to a constant frequency polyphase alternating current power source for starting and for full speed operation but is supplied by a variable frequency source in a single phase operating mode when reduced speed levels are desired In the single phase operating mode, low speed operation is provided by driving the motor with a cycloconverter which converts power from the polyphase source to single phase alternating current of a predetermined lower frequency The motor speed decreases from a higher level to a lower level by coasting, with gate signals of the cycloconverter suppressed until a desired lower speed is reached Initiation of contactor and cycloconverter operation is coordinated by motor speed sensing means

Optimisation program for large-induction-motor design

Abstract: The problem of designing large induction motors at a minimum cost is approached using nonlinear programming. The performance evaluation programs include saturation effects, stray load losses, and airflow and temperature rise throughout the machine, while the cost function includes labour as well as material costs. A new optimisation technique is employed which promises rapid convergence and allows the program to begin from, and search through, nonfeasible designs. This feature eliminates the need for a synthesis program as required in most optimisation methods. The program has been applied to motors in the range of 148–1 110kW.

AC Elevator control system

Abstract: In an AC elevator which is provided with a multi-speed induction motor unit connected to an AC power source and including a high-speed motor and a low-speed motor and in which an elevator car is started and accelerated by the high-speed motor, a control system comprising regenerative braking means connecting the low-speed motor to the AC power source through one set of thyristors connected in parallel in opposite polarity, DC braking means for supplying direct current to the high-speed motor from a controlled reactifier circuit, means for controlling the regenerative braking means to reduce the speed of the elevator car, means for detecting the reduction of the speed of the elevator car to a level at which the regenerative braking means is no more effective in producing the regenerative braking torque, and means for deenergizing the regenerative braking means and energizing the DC braking means in response to the output of the detecting means.

Slow-running DC motor with flat rotor for recording equipment - has stator windings coils fixed to ironless stator and projecting freely into air gap

Abstract: The slow-running dc motor, has a flat rotor and is used for driving recording equipment as in 2424290 2143752. It has the stator winding coils fixed on their outsides to the ironless stator and projecting feeely into the air gap. A spacer takes up the magnetically-generated axial force between the rotor parts on each side of the stator winding. This spacer fixes the rotor part to the inside of the stator winding and encloses with clearance the tube acting as rotor bearing. The spacer is bell- shaped. The bearing tube forms an integral part of the motor housing. The motor is designed to fit directly under the turntable of the recording equipment.

Variable threshold starting circuit for induction motor

Abstract: A circuit for the automatic starting of an induction motor of the type having a sensing means for producing a signal proportional to the main winding current and control means for allowing current flow through a start winding only when energized by a start winding control signal. The starting circuit includes means for continuously producing a variable threshold level which is proportional to a condition capable of affecting the current level in the main winding and which defines an adjustable threshold switching level. A comparison means continuously compares the adjustable threshold switching level to the signal proportional to the main winding current and, whenever the latter signal exceeds the former, the comparison means generates a start winding control signal which activates the start winding control means thereby establishing current flow through the start winding. When the main winding current decreases to a sufficient extent, the comparison means is characterized by the absence of a start winding control signal whereby the start winding control means will block the flow of current through the start winding.

Regulating the torque of an induction motor

Abstract: A motor control circuit and method for regulating the torque of an ac induction motor operated at a variable frequency utilizes as a controlled variable the modified in-phase component of stator current which is compensated for the voltage drop across the stator resistance. Both positive and negative torque are approximately linear assuming the slip frequency is changed linearly, and only the per phase line current and voltage are sensed. A traction application is described.

Modeling and simulation of variable-reluctance step motors with application to a high-performance printer system

Abstract: Basic information on modeling and digital computer simulation of variable-reluctance (VR) step motors is provided. The nonlinear equations of the system are derived, and a method for implementing them on a digital computer is presented. As an example, a typical printer with a step motor is designed with this approach. The problem is defined by giving the desired system performance criteria and the step motor parameters and characteristics. The specification of the control schemes determined the design. Computer simulation runs are made to determine the optimal control parameters of the system. The case study demonstrates the advantages of the computer-aided design, before the physical construction of the experimental system.

Solid state current source polyphase inverter induction motor drive

Abstract: A solid state, current source, polyphase inverter induction motor drive is disclosed wherein the current source is derived from a constant potential buss Each side of the buss is connected to the inverter via a separate chopper The choppers normally operate in unison to supply a controlled current to the inverter Each time the inverter sequence is to be advanced, the chopper current is reduced to zero on the side of the inverter, either positive or negative, that requires a commutation Chopper current is then reinstigated and feeds the next set of inverter thyristors in the inverter sequence Alternative means for rendering the current source non-inductive during inverter commutations, and transformerless means for providing motor voltages well above rated voltage are also disclosed

Multi-rotor electric motor

Abstract: A multi-rotor electric motor having a wound main rotor mounted on a drive shaft which is rotatable within a cup-shaped stator, which is so wound, that when connected to a source of polyphase power, as to provide a rotating magnetic field. A second rotor equipped with permanent magnets is mounted for rotation about and exteriorly of the stator and which are effected by the rotating magnetic field so as to tend to rotate the second rotor at synchronous speeds in the same direction as the main rotor. The two rotors are normally connected for mutual rotation between starting speed and pre-determined speed less than synchronous speed by a spring-closed centrifugally-opened clutch assembly which disengages when the main rotor reaches said pre-determined speed so as to enable both rotors to rotate independently of each other and which re-engages both rotors for mutual rotation when the speed of the main rotor falls below said pre-determined speed.