Showing papers on "Induction motor published in 1979"

Induction motor drive apparatus

Abstract: An induction motor drive apparatus of the type having a speed detector for detecting the rotational speed of an induction motor, speed command device for producing a command speed, and an error amplifier for amplifying a difference between the rotational speed of the induction motor and the command speed, the induction motor being driven by so controlling the amplitude of the primary current as to vary the amplitude of the secondary current in accordance with the difference between the rotational and command speeds. Included are two-phase sinusoidal wave generating device for generating two sinusoidal signals displaced in phase from one another by π/2 and whose amplitudes conform to the output of the error amplifier, primary load current arithmetic device for computing a primary load current by employing the output of the error amplifier and the output of the two-phase sinusoidal wave generating means, and primary current arithmetic means for computing a two-phase primary current command by adding the primary load current to the output of the two-phase sinusoidal wave generating device, which output serves as an excitation current. The induction motor is driven by the primary current command having an excitation current component and a primary load current component the amplitudes of which vary in accordance with the difference between the rotational speed of the induction motor and the command speed.

Development of a Modulation Strategy for a PWM Inverter Drive

Abstract: When induction motors are driven by electronic inverters, the applied voltage waveforms are quite nonsinusoidal. The fundamental component of the current is controlled by the load. The harmonic currents are limited principally by the motor leakage inductance and are independent of load. These harmonic currents can lead to increased motor heating and to increased peak currents. In addition, the modulation technique can give rise to problems in the control. An analysis method was developed to predict the performance of an induction motor in response to inverter waveforms. The correctness of the method was verified by comparison to measurements made on an operating system. This tool was then used to aid in the development of a modulation strategy, to accurately evaluate the motor heating problem and to analyze a new method of transitioning from pulsewidth modulation to square wave operation.

Base drive and overlap protection circuit

Abstract: An inverter (34) which provides power to an A. C. machine (28) is controlled by a circuit (36) employing PWM control strategy whereby A. C. power is supplied to the machine at a preselectable frequency and preselectable voltage. This is accomplished by the technique of waveform notching in which the shapes of the notches are varied to determine the average energy content of the overall waveform. Through this arrangement, the operational efficiency of the A. C. machine is optimized. The control circuit includes a microcomputer and memory element which receive various parametric inputs and calculate optimized machine control data signals therefrom. The control data is asynchronously loaded into the inverter through an intermediate buffer (38). A base drive and overlap protection circuit is included to insure that both transistors of a complimentary pair are not conducting at the same time. In its preferred embodiment, the present invention is incorporated within an electric vehicle (10) employing a 144 VDC battery pack (32) and a three-phase induction motor (18).

Compact variable speed drive for electric motor

Abstract: An electrical machine in which a frame supporting the rotor windings is coupled to the machine shaft through a planetary gear system housed within the rotor structure. The internal ring gear of the planetary system forms a part of the motor rotor structure. Further locking devices are provided to lock the various movable components making up the drive system together or to the motor casing so that a variety of speeds can be selectively attained at the output shaft or shafts of the motor without changing the motor speed.

Method of restarting induction motor and apparatus for carrying out the same

Abstract: A frequency detector produces a pulse train from an emf generated across a three-phase induction motor in the decelerating mode with its pulse repetition frequency proportional to the speed of the motor. A phase locked loop synchronizes this frequency with that of a variable frequency oscillator for a variable frequency inverter and the synchronization is maintained by the phase locked loop and a ramp generator controlled with the signal from the detector. When the detected frequency equals a command frequency from a reference circuit, the inverter starts to operate the motor. When the start operation has been completed, the phase locked loop is disabled while the ramp generator is connected to the reference circuit to change the frequency of the inverter to the command frequency to complete the restart operation of the motor.

Control system for electric motor vehicle

Abstract: A control system for an electric motor vehicle adapted to be driven by a group of induction motors, comprises a converter for producing an a.c. output to energize the group of induction motors, a frequency command circuit for producing a value representing a minimum number of rotations among those of at least two induction motors of the group added with a slip frequency in a power running mode of the vehicle on one hand and a value representing a maximum number of revolutions among those of at least two given induction motors of the group subtracted by the slip frequency in a regenerative braking mode, respectively, the values being utilized as frequency control commands, and a frequency control circuit for controlling the output for controlling the output frequency of the converter in dependence on the frequency control commands, thereby to improve the adhesion performance of the electric motor vehicle.

Variable speed induction motor control system

Abstract: A variable speed induction motor control system includes a variable voltage DC bridge coupled to a frequency controlled power inverter which in turn drives an induction motor. A motor power factor detecting circuit determines the relative voltage/current phase angle for the motor and derives a corresponding power factor error signal. The DC bridge and inverter respond to the power factor error signal to maintain the input power conditions of the motor at a near optimum efficiency. The power factor detecting circuit uses an exclusive OR gate to provide a pulse having a duration corresponding to the motor power factor which enables a counter during the pulse interval. After each pulse, the count which is indicative of the motor power factor, is applied to a holding circuit and converted to an analog error voltage.

Synchronous Control of a Static AC Induction Motor Drive

Abstract: Conventional methods of controlling an induction motor utilize regulation of stator current and motor slip frequency in order to maintain system stability. This control strategy requires a shaft speed feedback and fast-response current regulation. An alternative method of controlling an induction motor is presented which achieves the necessary system stabilization by controlling only the motor frequency. The control inherently regulates the motor torque angle by properly adjusting the phase of the converter firing signals. By synchronizing the inverter firing pulses to the motor back electromotive force (EMF) possible adverse inverter operating modes are avoided. The concept of synchronous control eliminates the preprogrammed functional relations previously required and allows the control to adapt to any desired motor flux level. Any desired outer regulating loop can be incorporated to form a fast-response wide-range ac drive system.

Control Loop Study of Induction Motor Drives Using DQ Model

Abstract: This paper presents a systematic study of the various control loops in a current source inverter-induction motor drive and their effects on the dynamic response and stability of the system. A dq model is developed which incorporated the induction motor and the inverter power supply with current feedback. The model is first used to generate steady-state curves to determine operating points. A linearized small signal model is developed to study stability and provide transfer functions for various control strategies. The stabilizing effect of adding first slip speed control and then flux control is investigated. Two possible implementations of the flux control are compared, showing insignificant difference. The study reveals that with flux control, several pole-zero cancellations are possible, thereby simplifying the model and the design of other outer control loops such as speed or torque.

Losses and Parasitic Torques in Electric Motors Subjected to PWM Waveforms

Abstract: Some aspects of the theoretical performance of an electric motor, supplied by an unfiltered pulsewidth modulated (PWM) inverter are studied. The stator copper losses and the winding insulation lifetime are emphasized. An induction motor system is assumed and the creation of low-frequency parasitic torques are described. Their relative importance are estimated. It is shown that PWM supplies may have a negative impact on the motor performance and lifetime and can make a modification of the motor design more desirable than in the case where a ``simpler'' inverter system is used.

PWM Inverter control and the application thereof within electric vehicles

Abstract: An inverter (34) which provides power to an A.C. machine (28) is controlled by a circuit (36) employing PWM control strategy whereby A.C. power is supplied to the machine at a preselectable frequency and preselectable voltage. This is accomplished by the technique of waveform notching in which the shapes of the notches are varied to determine the average energy content of the overall waveform. Through this arrangement, the operational efficiency of the A.C. machine is optimized. The control circuit includes a micro-computer and memory element which receive various parametric inputs and calculate optimized machine control data signals therefrom. The control data is asynchronously loaded into the inverter through an intermediate buffer (38). In its preferred embodiment, the present invention is incorporated within an electric vehicle (10) employing a 144 VDC battery pack (32) and a three-phase induction motor (18).

Control apparatus for induction motor

Abstract: An induction motor has a multi-phase primary winding (stator winding) and a multi-phase secondary winding (rotor winding) which are connected to each other in opposite phase relation The both windings are fed with variable frequency AC current from a common frequency converter A position sensor for sensing a rotor position is mounted on the induction motor The position signal of the position sensor is in phase with an air gap flux between the primary winding and the secondary winding Magnitude of a motor current is controlled in accordance with a torque command signal indicative of an error between a speed command signal and a speed feedback signal and with a voltage command signal for determining a terminal voltage, and a phase difference of the motor current relative to the position signal is controlled in accordance with the torque command signal and the voltage command signal In this manner, the torque generated can be varied while maintaining amount of air gap flux and hence the terminal voltage constant

Two-Frequency Heat Run - A Method of Examination for Three-Phase Induction Motors

Abstract: The system equations for a three-phase induction motor fed at two frequencies are derived. The system of equations for the steady-state quantities, characterizing the average steady- state operating point, and for the "deviations" which determine the superposed multi- frequency oscillations, are established. The scope and the mutual dependenceof the systems of equations do not permit a general analytical solution; they have to be solved by numerical iteration. Considering the results obtained by numerical calculation , the operational behaviour of the three-phase induction motor fed at two frequencies is discussed. A heat run performed with the induction motor by the two-frequency method and the results obtained are compared with the results of a conventional heat run in which the motor shaft is mechanically loaded. It is found that, provided the voltage and frequency of the back-up system are judiciously chosen, the noinal temperature rise in the induction motor can be accurately determined by the two-frequency method.

Existence of limit cycle and stabilization of induction motor via new nonlinear state observer

Abstract: In this paper the boundedness of the solutious of the bilinear and nonlinear differential equations, which describe the dynamic behavior of an ideal three-phase squirrel cage induction motor, is shown using a Lyapunov function. It is then proved by sampling combined with a digital simulation that an unstable machine has limit cycle. Utilizing these results a new bilinear and nonlinear reduced-order state observer, which is globally asymptotically stable, is constructed to estimate the unmeasurable state variables. By using this observer a new two-step procedure for stabilizing an unstable machine, which has a limit cycle, is proposed. This scheme can be easily implemented resulting in an asymptotically stable overall system. These results are numerically verified by simulation.

Energy economizer for polyphase induction motors

Abstract: A standard three phase induction motor starts with all three of its input connections connected to the three phase power line. Two of these connections are through triacs which remain continously conducting below said motor's particular most energy-efficient speed, which is above about 95% of synchronous speed. This assures full starting torque and undiminished overload handling capability. The triacs, in response to a control signal, may open the circuits over a sufficiently wide portion of the sine wave input voltage to substantially maintain said particular efficient speed under all rated load conditions. To assure smooth operation and maximum energy savings, the two triacs conduct differently at very light motor loads. The DC control voltage which determines the operation of the triacs is generated by a frequency discriminator circuit which receives its information from a load detecting device that is frequency modulated by load/speed related properties inherent to induction motors.

Bearing failure indicator for rotating electric machines

Abstract: In a squirrel cage type of induction motor, conductive strips insulated from the stator are circularly spaced, ninety degrees apart, and project 0.003 inches into the rotor-to-stator clearance space. Upon excessive lateral rotor movement, it contacts a strip, closing a low voltage circuit triggering an alarm and de-energizing the motor. A reset button must be pressed to enable starting the motor.

Electronic motor having a multi-pole external rotor

Abstract: An electronic motor has a multi-pole external rotor and a multi-slot stator which is rotatable inside the external rotor. At least two magnetic field sensing elements are arranged in the vicinity of the external rotor and current supply to the stator windings is provided by a commutation device. The prior art stator was provided with obliquely set stator winding slots and involved a complicated winding technique. To eliminate this disadvantage and to be able to use slots lying parallel to the axis, the neutral field lines between each north and south pole of the external rotor are made to lie parallel to the rotor axis in the region of the magnetic field sensing elements and obliquely thereto in the region of the laminated rotor stack.

Digital Phase-Locked Loop for Induction Motor Speed Control

Abstract: The study of the speed control of induction motor drive using digital phase-locked loop is discussed. The block diagram and the control circuitry have been outlined. A mathematical model has been developed to predict the system performance. Different types of filters have been considered as part of the feedback control system, and their effects on the overall system behavior have been qualitatively studied. The system is tested using a 5-hp induction motor and an integrating type filter. Excellent speed regulation in the order of 0.002 percent has been obtained.

Hybrid stator and a two-axis induction electric motor constructed therewith

Abstract: A tubular stator capable of creating a magnetic field having both linear and rotary components comprises a tubular magnetic frame formed from longitudinal magnetic elements which are angularly spaced. The magnetic elements have teeth which extend radially inwardly. Circular induction coils are disposed between the teeth and undulating coils are disposed longitudinally between the magnetic elements. A magnetic sleeve surrounds the magnetic frame. An electric motor comprises a cylindrical rotor mounted within the tubular stator so as to be rotatable and translatable.

Variable speed motor system

Abstract: An electronic system for controlling the speed of a shaded-pole single-phase induction motor provides increased power during speed increase and automatic braking during slowdown by regulation of half-wave D.C. braking current applied to the motor. Speed control during normal operation, and braking control during slowdown and stopping, are implemented by means of dual feedback loops interactively connected to the gate electrode of a triac in the A.C. current line of the motor. The speed control loop utilizes a frequency/phase detector to adjust the time delay of triac gating relative to the zero crossing points of each half-cycle of A.C. voltage until the tachometer-sensed speed of the motor corresponds to a desired speed set by a voltage controlled oscillator. The braking control loop adjusts the time delay of the triac gating relative to the zero crossing points of every alternate half-cycle of A.C. power thus decelerating the motor by an impressed half-wave pulsed D.C. current.

A New Controlled Current Type Inverter with Improved Performance

Abstract: A new current-commutating method applying the action of the mutually coupled inductances is described and is termed the coupled reactor commutating (CRC) method. With this method a unique self-excited controlled current type inverter is constructed. The CRC inverter not only gives an efficient voltage adjustment function, but it also liberates men from the task of treating reactive powers. An example of the application to the induction motor drives is described in which an overall efficiency as high as 85 percent has been reached. The troublesome problem of parasitic torque pulsation in the low-revolution range, which is inherent in the controlled current type inverters, is also resolved by the torque-smoothing current control method with the CRC inverter.

A New Method for the Study of Inter-Bar Currents in Polyphase Squirrel-Cage Induction Motors

Abstract: The paper presents an analysis of inter-bar currents and stray-load losses in non saturated polyphase squirrel-cage induction motors due to the harmonic currents in the cage and in the contact between cage and rotor laminations.

Microprocessor control of a PWM inverter induction motor drive

Abstract: The practical implementation of a microprocessor control system for an induction motor drive is described. A three-phase transistor inverter feeds a 2 hp induction motor with a pulsewidth modulated voltage waveform having no harmonic component of lower order than the seventeenth. The motor operates in a controlled-slip mode and both constant torque and constant horsepower strategies are implemented.

Application of Induction Motor Simulation Models to Power Station Auxiliary Pump Drives

Abstract: Transient operation, such as that caused by faults or switching, often results in auxiliary drive motors departing significantly from their normal operating speed. Under these conditions it is necessary to take account of parameter changes caused by saturation and eddy current effects. The paper presents a mathematical model which utilises a modal technique to represent eddy currents and includes saturation effects. The model also included a representation of the mechanical system. A number of important operating conditions are simulated and comparisons of test and computed results are presented for a test machine.

Experience with direct and indirect search methods applied to cage induction motor design optimization

Abstract: In the present paper low cost cage induction motor design problem is approached using direct search methods, which do not require to calculate the derivatives of the function, and indirect method-a penalty function approach. Induction motor design is considered as a nonlinear, multivariable constrained optimisation problem with ampere conductors per meter, ratios stack length to pole pitch and stator slot depth to width, stator core depth, average air-gap flux density, and stator and rotor winding current densities as variables. The constraints are imposed on the thermal ratings of the machine and on performance indices- Results for same capacity motor with different optimization techniques are tabulated and compared.

Choice of parameters in the hybrid permanent-magnet synchronous motor

Abstract: Hybrid permanent-magnet reluctance motors have to be designed with many performance parameters in mind. The configuration is not a simple one, and some parts of the magnetic circuit operate in the nonlinear regime. The effect of the choice of design dimensions is considered, and the effect on pull-out torque computed as some of the important paramenters are varied. It is seen that some design parameters have a major effect on performance, although others are much less critical.

A Theoretical Analysis of Linear Induction Motors

Abstract: This paper describes a quasi-three- dimensional mathematical model developed for the design of linear induction motors operating with either controlled current or controlled voltage supplies. The model is notable in its simultaneous treatment of (1) electromagnetic boundary phenomena, including longitudinal end-effect and transverse edge-effect; and (2) other refinements, such as the effects of staggered double-layered windings, and a secondary resistance corresponding to the actual current pattern. The mutual interaction of these characteristics is encompasssed in the model. Motor performance predictions obtained from the model have agreed with full-scale hardware test results.

Apparatus and method for providing a signal proportional to flux in an AC motor for control of motor drive current

Abstract: An apparatus and method for providing signals indicative of the magnitude and angular position of the DC motor flux of an AC induction motor is disclosed. The AC induction motor provides controllable rotation and torque in accordance with a drive current of variable magnitude and frequency. A first signal is provided proportional to the rate of change of the flux of the motor. A second signal is supplied proportional to the magnitude of the drive current. A flux signal is generated proportional to the integral of the first signal when the frequency of the output signal is above a preselected value and which is proportional to the second signal when the frequency of the output signal is below the preselected value. A representative value for the preselected frequency value is 3 Hertz in a 60 Hertz drive system. The flux signal is effective to control the generation of the drive current. An embodiment of the present invention is shown for the case where the motor is stopped at a predetermined position in accordance with a predetermined conduction state of the inverting supplying the drive current. Additional embodiments are shown for the general cases where the motor can be stopped at any position and where two flux axes or three flux axes are sensed. The present invention is particularly applicable for use in an AC induction motor drive system.