Showing papers on "Induction motor published in 1988"

Direct self-control (DSC) of inverter-fed induction machine

Abstract: The new direct self-control (DSC) is a simple method of signal processing that gives converter-fed three-phase machines an excellent dynamic performance. To control the torque of, say, an induction motor, it is sufficient to process the measured signals of the stator currents and the total flux linkages only. In the basic version of DSC, the power semiconductors of a three-phase voltage source inverter are directly switched on and off via three Schmitt triggers, comparing the time integrals of line-to-line voltages to a reference value of desired flux, if the torque has not yet reached an upper-limit value of a two-limit torque control. Optimal performance of drive systems is accomplished in steady state as well as under transient conditions by combination of several two-limit controls. >

Modeling of permanent magnet motor drives

Abstract: Research has indicated that the permanent magnet motor drives, which include the permanent magnet synchronous motor (PMSM) and the brushless DC motor (BDCM) could become serious competitors to the induction motor for servo applications. The PMSM has a sinusoidal back EMF and requires sinusoidal stator currents to produce constant torque while the BDCM has a trapezoidal back EMF and requires rectangular stator currents to produce constant torque. The PMSM is very similar to the wound rotor synchronous machine except that the PMSM that is used for servo applications tends not to have any damper windings and excitation is provided by a permanent magnet instead of a field winding. Hence the d, q model of the PMSM can be derived from the well-known model of the synchronous machine with the equations of the damper windings and field current dynamics removed. Because of the nonsinusoidal variation of the mutual inductances between the stator and rotor in the BDCM, it is also shown that no particular advantage exists in transforming the abc equations of the BCDM to the d, q frame. Hence the solution of the original abc equations is proposed for the BDCM. >

Noninvasive detection of broken rotor bars in operating induction motors

Abstract: A description is given of a computer-based noninvasive broken bar fault detector for squirrel-cage rotors of induction motors. The detector can be applied to existing motors without disassembly or shutdown and has the sensitivity to diagnose the presence of a single broken bar or an open end ring. It is suitable for monitoring the trend of the motor signature, or it can be used as a one-time diagnostic tool. >

Modelling of inductance machines for electric drives

Abstract: The author presents several linear and nonlinear models suitable for transient and steady-state analyses of induction machine drives The models are presented in equivalent circuit form to preserve the identity of nonlinear parameters The circuits, designated as Gamma or inverse Gamma form, are simpler than the conventional T-form circuit Their parameters are readily determined from terminal measurements The major effects of magnetic nonlinearity are included in the models in a way that is more accurate than that usually obtained with the conventional T-form circuits Modeling of time harmonics is also discussed >

A stator flux oriented induction machine drive

Abstract: The sensitivity of the parameters of a rotor-flux-oriented system using rotor flux estimation is discussed, and a stator-flux-oriented scheme is developed. Since the estimation of the stator flux is independent of the leakage, the steady-state performance of the stator-flux-oriented system is insensitive to the leakage inductance. A decoupler is designed to minimize the coupling in the stator-flux reference frame, improving the dynamic performance of the system. Digital simulation is carried out to show that the performance of the stator-flux-oriented system is superior to that of a detuned rotor-flux-oriented system. >

A simplified approach to continuous on-line tuning of field-oriented induction machine drives

Abstract: A simplified approach to continuous, online tuning of rotor flux feedforward, field-oriented induction machine drives is presented. The procedure offers the advantages of not requiring a special test signal or special test conditions. The approach takes advantage of the stator voltage equations, which allow robust, parameter-insensitive estimation of the electromagnetic torque while operating at nominal speeds for which the stator voltage (IR) drop is negligible ( mu approximately 5 Hz and above). This torque computation is independent of the rotor flux field-oriented control. In essence the approach uses a stator flux controller to detect improper tuning of the feed forward, rotor flux controller. The authors present the theoretical and practical implementation of such a continuous, self-tuning system. Experimental results are based on a rotor flux feedforward, field-oriented induction machine servo drive. >

The universal field oriented controller

Abstract: This paper synthesizes and develops a universal field oriented (UFO) controller for induction machines The UFO controller decouples flux and torque in an arbitrary flux reference frame Due to its high degree of generality the UFO controller lends itself to be fully compatible with all existing field oriented controllers, indirect as well as direct field orientation As a consequence, the digital implementation of the UFO scheme is identical for all induction motor drives enabling the usage of identical hardware and software Examples of UFO control block diagrams for different field oriented controllers are presented The execution time of the UFO algorithm is compared with the classical rotor flux field orientation method when using a high speed digital signal processor Further, this paper indicates that the flexibility of changing the flux reference frame can extend the stability region of the drive especially at high speed during flux weakening Detuning problems in field orientation are handled in an optimal manner for each field oriented controller by proper selection of the model of the induction machine and its reference frame >

Recent progress in the development in solid-state AC motor drives

Abstract: The author summarizes important developments in AC drive design that have occurred in the past several years. He discusses: converter technology, covering the matrix converter, PWM voltage and current link converters; and resonant link converters; AC motor technology, covering stepping motor drives, DC brushless motor drives, and synchronous reluctance motors; and control technology for AC drives, covering online and offline parameter identification and efficiency-maximizing control. >

Induction motor analysis by time-stepping techniques

Abstract: A numerical approach is described that overcomes the deficiencies of other methods through the use of a two-dimensional, nonlinear, time-stepping finite-element method for excitation from a constant voltage source. Comparison of stator current for no-load and load conditions shows good agreement with test values on a large induction motor. It is shown that the method can provide a great deal of information on flux distribution and harmonic rotor bar currents. >

Studies on the use of conventional induction motors as self-excited induction generators

Abstract: The suitability of using a normal three-phase induction motor as a capacitor self-excited induction generator (SEIG) is illustrated. The thermal limit of the stator windings being the limiting factor, the capacity of the SEIG is determined. The steady-state performance of such induction generators, maintaining a constant terminal voltage, is analyzed under resistive and reaction loads. Typical experimental results are also presented. It was found that, for low power motors, the maximum power that can be extracted as generators is 148% to 160% of the motor rating for resistive loads and 118% to 128% of the motor rating for 0.8 lagging power factor loads. Capacitive reactive volt-ampere (VAR) required to maintain constant voltage at 1.0 p.u. speed is in the range 85% to 140% of the power rating of the motor with resistive loads and 100% to 140% with lagging reactive loads. >

An integrated AC drive system using a controlled-current PWM rectifier/inverter link

Abstract: Two identical three-phase, bipolar transistor, controlled-current, pulsewidth modulation (PWM) power modulators are integrated so that one functions as a rectifier and the other as an inverter in an AC drive system. The rectifier input currents maintain near-60-Hz sinusoidal waveforms with unity power factor. A leading power factor is also possible. The modulators do not depend on the availability of bidirectional switch elements. Performance as a polyphase induction motor drive under motoring and regenerative braking is reported. The study includes digital simulation of operation as a synchronous motor drive. >

Finite element force calculation: comparison of methods for electric machines

Abstract: Results of torque and thrust calculation using the finite-element method are presented. The calculations make use of the Maxwell stress tensor, the virtual work principle, and the Lorentz formula. Calculations for two types of machines are considered: the switched reluctance motor and the linear induction motor. Computational results are validated by comparison with the shortcomings and the advantages of the different methods. >

Studies on inverter-fed five-phase induction motor drive

Abstract: The advantages of higher-phase-order drives are reviewed, and results of investigations of a five-pulse inverter-fed induction motor are presented. Methods of improving the waveform of the motor phase current in the five-phase drive are examined theoretically as well as experimentally. A mathematical model based on complex symmetrical components is developed for theoretical investigations, and a prototype five-phase inverter-fed induction motor drive is fabricated to conduct experimental studies. Theoretical and experimental results under various operating modes are presented. The studies establish that the five-phase drive operates satisfactorily when it is fed from a pulsewidth-modulated inverter. >

Review of recent progress in linear motors

Abstract: The paper gives a review of recent progress in linear electrical machines The use of linear machines for industrial purposes is described and this is followed by a report of their application to transport propulsion and levitation The development of linear forms of induction motor, synchronous motor, stepper motors, DC motors, permanent magnet motors and reluctance motors is described A description of most major experimental and implemented transport projects using linear motors is provided, along with the reported performances of the different arrangements The paper concludes with a review of the analytical techniques used to obtain the performance of linear machines A description of direct-solution layer methods, and finite-element techniques is given, with a comparison of accuracies achieved by each method

Method and apparatus for brushless DC motor speed control

Abstract: Control and synchronization of a polyphase, brushless DC motor (used for a hard-disk system) during initial start-up of the motor, is effected by monitoring rotor position using a high-frequency commutation: A short current pulse is applied to each power phase of the motor, and motor current conducted in response thereto, is measured to determine therefrom positional information of the rotor From such positional information the identity of the appropriate motor phase to which is applied a torque-producing current is determined Cycles of high-frequency commutation and application of torque-producing are performed, until the rotational speed of the rotor has attained a predetermined RPM Motor speed is controled in synchronized, increasing fashion by continued monitoring of the motor current and back-EMF, until a desired rotational RPM is attained, whereupon torque-producing current is sequentially applied to each motor phase in synchronization with the rotor position by deriving positional information from the disk

A complete equivalent circuit of a linear induction motor with sheet secondary

Abstract: A per-phase equivalent circuit of a linear induction motor (LIM) with sheet secondary is developed with parameters derived from field analysis, taking the specific phenomena of longitudinal-end effect, transverse-edge effect, field diffusion in the secondary, and back-iron saturation into account. The results are applied to two single-sided LIMs, and their performance is predicted. Results from analyses are compared with those obtained from tests. >

Decoupling control of induction motor drives

Abstract: The decoupling control of induction machines is investigated. Three different schemes for decoupling-control methods based on stator flux, airgap flux, and rotor flux field regulation are developed. The control dynamics of each scheme are outlined and studied. Simulation results are presented to verify that these schemes provide decoupling control with excellent dynamic behavior. The transient and steady-state relationships between slip frequency and torque, under constant stator flux, airgap flux, and rotor flux operations, are simulated and compared. The sensitivity characteristics of the three methods of flux-control, machine fed by impressed currents and voltages, are also compared and studied. A prototype torque-drive system is implemented to demonstrate the decoupling control of a squirrel-cage induction machine. >

Single phase induction motor with an electronically controlled capacitor

Abstract: A single-phase induction motor using an electronically controlled capacitor is described. The system uses a DC capacitor switched by a transistor H bridge. By proper control of the transistor switching, the circuit synthesizes a continuously variable capacitance in series with the auxiliary winding. The system could be used to replace standard single-phase motor capacitor configurations to provide improved machine performance. The basic system is described and compared with a normal capacitor-run motor. The effects of independent adjustments in several system parameters are considered, and the circuit device requirements are described. Both analog and digital simulations are used to carry out the analysis. Illustrations of some of the design flexibility inherent in the system are included. >

Control strategy for a three phase AC traction drive with three-level GTO PWM inverter

Abstract: A control strategy developed for two-level inverters is applied to the three-level gate-turn-off PWM inverter. This is done by replacing the three-level inverter by two coupled two-level inverters and taking the coupling condition into account. A control strategy based on the method of direct self-control is described. Results from computer simulation for a traction motor with 1400 kW nominal power are shown and discussed. >

Analysis of rotor failures in squirrel-cage induction motors

Abstract: The authors describe a procedure for analyzing rotor failures in squirrel-cage induction motors. They attempt to identify the various kinds of failure classes and patterns and relate them back to the probable cause of failure. They discuss five key areas that must be considered and related to one another in order to accurately diagnose the cause of rotor failure: failure class, failure pattern, appearance, application, and maintenance history. Finally, a summary of typical failures and tell-tale rotor appearances is presented. >

Efficiency-optimized flux trajectories for closed-cycle operation of field-orientation induction machine drives

Abstract: A structured design procedure for system integration is presented. A dynamic programming scheme is developed which optimizes efficiency of an induction-machine drive which is operated in closed-cycle and which has both control and state constraints. Application of rotor-flux feed-forward field-orientation control for an induction machine reduces the system equations to contain only three state variables: rotor flux, velocity, and position. Maximum stator current and rotor velocity are set as constraints. Saturation effects are modelled to provide a state-dependent constraint on the rotor-flux magnitude. Load is treated as a function of the rotor position, which is appropriate for many mechanical system applications. To optimize efficiency for closed-cycle operation of the motor, both machine losses as well as the cycle time must be minimized using an appropriate objective function. State trajectories of the system that simultaneously optimize machine efficiency and cycle time are found by dynamic programming. Flux trajectories for the optimal solution are found to vary significantly over the machine cycle. The validity of the energy optimization is investigated experimentally on a feedforward, field-oriented induction machine. >

A novel technique for optimal efficiency control of a current-source inverter-fed induction motor

Abstract: A technique that optimizes flux level to improve the efficiency of an induction motor is discussed. When harmonics and saturation effects are considered, the slip of minimum loss, or optimal slip, depends on both the speed and the load torque. The measurements of speed and torque are achieved without conventional torque and speed sensors, using motor terminal quantities. The control strategy is divided into two stages. First, the optimal slip is searched by trial and error, and the results are tabulated in microprocessor memory. Then the motor is operated at optimal efficiency by simply tracking the optimal slip given in the table. Experimental results show good performance in energy saving and dynamic responses. >

Design and performance of a high frequency link induction motor drive operating at unity power factor

Abstract: The design and performance of a complete three-phase converter system and field-oriented induction motor drive based upon a 20 kHz AC link is described. By using the same converter for the AC input side and the output load side, it is shown that power can be transferred in either direction. It is also shown that, with the use of a current regulator, both power flow on the link and the link voltage amplitude can be regulated. In addition, by suitable feedback control, the power factor at the input to the converter can be adjusted to unity. Both computer and experimental results show unity power factor operation, low harmonic current in both the input and output of the system, and bidirectional power flow capability. >

Parameter estimation for induction machines based on sensitivity analysis

Abstract: Induction machine parameters supplied by manufacturers are usually sufficient for short-circuit analysis only. System studies that involve transient simulation of machines require additional parameters that are not readily available, but nonetheless are essential for an accurate modeling of the machines. A mathematical method for estimating the equivalent circuit parameters of induction machines from the most readily available performance characteristics is presented. In this method, machine equations are used to estimate the parameters and sensitivity analyses are then performed with respect to the circuit parameters to match the given performance characteristics. An example is included to illustrate how well the performance of the estimated model matches that of the actual machine. The example is a three-phase, 1000 HP, 4.16 kV, 60 Hz induction motor. The example indicates that, with a restricted set of input data, it is possible to find the elements of a machine model that duplicates the given performance to a high degree of accuracy. Without sensitivity analysis, accuracies on the order of 10% are obtained, but after sensitivity analysis an accuracy of 0.1% or better can be achieved. >

A wide constant power range vector controlled AC motor drive using winding changeover technique

Abstract: A high-performance vector-controlled induction motor drive with a very wide constant power range of 1:10 to 1:30 has been developed and widely accepted in the spindle drives of machine tools. The motor has two combinations of winding connections, and one of them is selected in accordance with the operating conditions. The versatility of the winding changeover technique has been introduced and demonstrated. A wide constant power range is achieved, and the gear box used in a conventional machine is eliminated. In addition, it was proved by actual operations that the machining operation can be continued during the changeover without sacrificing the quality of the final product. The basic idea, features, and test results of this technique are described. >

A high performance control method of a voltage-type PWM converter

Abstract: A high-performance control method for a voltage-type pulsewidth-modulated voltage-type converter is introduced. Starting from the modeling of the converter, power-factor control and five types of DC voltage control are discussed. The stability and responses of these control methods are analyzed and compared with the root locus method and by digital simulation. The most promising approach, which uses current feedforward control, is applied to the drive test of an induction motor, and its excellent performance is confirmed. >

A direct field oriented controller for induction motor drives using tapped stator windings

Abstract: The implementation of a direct method of field orientation that requires little knowledge of machine parameters and uses only readily measurable quantities is discussed. The system uses tapped stator windings to measure the air-gap flux. The signals from the tapped windings are also used in a flux-regulation loop. A speed controller is implemented using the ripples created in the tapped windings by the motion of the rotor slots through the flux for speed information. >

Method and apparatus for providing thermal protection for large motors based on accurate calculations of slip dependent rotor resistance

Abstract: A microprocessorized thermal protection system and accompanying method measures input voltage and current of an induction motor and derives therefrom continuously updated estimates of the slip dependent rotor resistance during acceleration of the motor. The measurements and calculations of the varying rotor resistance enable determination of the heat generated within the motor based on a thermal model thereof. Phase shift distortions induced by the measurement system are accounted for by determining the value of the stator resistance at start up. In addition, during a brief period following start up, sampling of the voltage/current inputs is suspended to avoid the effects of the initially occurring DC-offset resulting from the application of the voltage input to the inductive motor load.

Alternating current motor control system with emergency control responsive to failure of power supply

Abstract: A control system for an alternating current motor, such as an elevator hoisting induction motor, in response to failure of power supply, such as service interruption, phase open and so forth, performs in a first emergency control mode and in a second emergency control mode. In the first emergency control mode operation, dynamic braking is used to decelerate the motor. On the other hand, in the second emergency mode, triggered while the motor is driven in regeneration mode to recirculate regenerated power to decelerate the motor, a mechanical brake is applied. During second emergency control mode operation, power supply condition is monitored to detect failure of the power supply for switching control mode from the second emergency control mode to the first emergency control mode. Switching from the second emergency control mode to the first emergency control mode assures synchroneous operation of an inverter and the motor after resumption of power supply to the motor in cases where the power failure is short in duration.

An improved resonant DC link invertor for induction motor drives

Abstract: The authors present a bidirectional initial current control concept which solves the voltage overshoot problem in the resonant link and establishes reliable zero-voltage crossing for smooth inverter operation. The resonant circuit is analyzed to establish the criteria for initial current selection. A circuit is proposed to establish the bidirectional initial current. The improved inverter permits successful operation at 50 kHz resonant frequency and can potentially operate up to 100 kHz. The control of the inverter, which involves prediction of the inverter input current, is formulated. A complete inverter-fed induction motor speed control system is simulated using PC-SIMNON. The simulation study at both 50 kHz and 25 kHz resonant frequency indicates the superiority of the inverter at higher resonant frequency. >