Showing papers on "Induction motor published in 1991"

DSP-based speed adaptive flux observer of induction motor

Abstract: A method for estimating the rotor flux and speed of an induction motor based on adaptive control theory is presented. The method is applied to a direct field-oriented induction motor control without speed sensors. The influence of the parameter variation on the speed estimation can be removed by the proposed parameter adaptive scheme. The validity of the adaptive flux observer is verified experimentally. >

Lumped parameter thermal model for electrical machines of TEFC design

Abstract: A lumped-parameter thermal model is described which provides both a steady-state and transient solution to the temperatures within an electrical machine of the TEFC design. The model is sufficiently complex to identify the temperatures at most locations in the machine, including the peak temperatures in the endwinding and the surface temperatures of the rotor. It is formulated out of purely dimensional information and constant thermal coefficients and is therefore easily adapted to a range of frame sizes. The thermal behaviour of the TEFC machine is accurately described by the solution of just eight linear differential equations. The model is therefore suitable for application to online temperature estimation for protection and duty-cycle evaluation. The application of the thermal model to a medium (75 kW) and two small (5.5 kW) induction motors is described in detail. The model performance is confirmed by experimental temperature data obtained from varying load tests on each of the three induction motors.

Cause and analysis of stator and rotor failures in three-phase squirrel-cage induction motors

Abstract: The authors attempt to identify the various causes of stator and rotor failures in three-phase squirrel cage induction motors. A specific methodology is proposed to facilitate an accurate analysis of these failures. It is noted that, due to the destructive nature of most failures, it is not easy, and is sometimes impossible, to determine the primary cause of failure. By a process of elimination, one can usually be assured of properly identifying the most likely cause of the failure. It is pointed out that the key point in going through this process of elimination is to use the basic steps of analyzing the failure class and pattern, noting the general motor appearance, identifying the operating condition at the time of failure, and gaining knowledge of the past history of the motor and application. >

Speed sensorless field orientation control of the induction machine

Abstract: A speed estimation method for an induction machine and its application to a flux observer-based field orientation (FOFO) control system proposed previously is presented. The motor speed is estimated on the basis of the difference between two flux estimators. The convergence of the method is analyzed, and a novel pole assignment method is proposed. The speed estimator is applied to the FOFO controller. The system has been implemented using a DSP, and some laboratory experiments showing that the speed-sensorless FOFO operates with enough stability and has a strong robustness to rotor resistance variation are reported. >

Transient effects in application of PWM inverters to induction motors

Abstract: Standard squirrel cage induction (SCI) motors are subjected to nonsinusoidal wave-shapes when supplied from adjustable-frequency inverters. In addition to causing increased heating, these wave patterns can be destructive to the insulation. In particular, pulse-width-modulated (PWM) inverter output amplitudes and risetimes are investigated. Motor insulation capabilities are discussed. Voltage reflections are simulated for various cable lengths and risetimes and are presented graphically. Simulations confirm potential problems with long cables and short risetimes. Application precautions are also suggested. >

A strategy for improving reliability of field oriented controlled induction motor drives

Abstract: Although design of induction motor drives employing field-oriented control has reached a relatively mature state, relatively little effort has been expended on improving the reliability of these drives. A new, improved induction motor drive topology and control strategy are proposed that allow for continuous, disturbance-free operation of the drive even with complete loss of one leg of the inverter or motor phase. A complete analysis and computer simulation of the control and circuit concepts is included. >

Analysis of a concentrated winding induction machine for adjustable speed drive applications. I. Motor analysis

Abstract: The performance of multiphase machines designed for operation with static power converters is investigated. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Equations which define the transient as well as steady-state behavior, including the computation of all machine inductances, are derived. In deriving these equations the space harmonics are specifically included. Equations for calculation of terminal voltages and electromagnetic torque are modified to account for nonsinusoidal air-gap-flux distributions. A conventional three-phase induction motor including the effect of space harmonics is simulated. >

Adaptive-speed identification scheme for a vector-controlled speed sensorless inverter-induction motor drive

Abstract: The authors describe a model reference adaptive control system for speed control of the vector-controlled inverter induction motor drive without a speed sensor. The rotor speed is estimated with a full-order adaptive observer and is used as the feedback signal for the vector and speed controls. In order to estimate the speed accurately at low speeds, the motor stator resistance is also identified at the same time to correct the mismatched resistance value used in the observer. The resulting system is verified to be hyperstable. As a result, the drive can be operated in a wide range of speed, and especially, it can be operated stably at the state of zero speed. Experiments also show that the scheme is effective. >

Split phase induction motor operation from PWM voltage source inverter

Abstract: The operation of split-phase induction motors from pulse-width modulated (PWM) voltage source inverters is examined. Splitting the phase windings leads to reduced voltage ratings for the inverter switches. As compared with seven positions for the space phasor of voltage in three-phase machines, 48 different locations bounded by a 12-sided polygon are possible in the split-phase machine. Based on space phasor modulation, a three-phase inverter can give a maximum peak fundamental of 0.577 V/sub DC/. In comparison, the split-phase configuration can provide an equivalent three-phase maximum peak fundamental of 0.643 V/sub DC/ with a DC bus voltage of 0.5 V/sub DC//cos 15. >

Observers for induction motor state and parameter estimation

Abstract: The Kalman filter in its basic form is a state estimator and can be applied to the problem of estimating induction motor rotor currents in a vector control scheme. This filter is shown to combine information from the plant model with output measurements to produce an optimal estimate of the unmeasured states. Also described is the application of the extended Kalman filter algorithm to the online estimation of rotor resistance in an induction motor drive. Significant savings in computing requirements are obtained with a reduced-order model of the motor, in which measured, rather than computed, values of stator currents are used. >

An improved estimation of iron losses in rotating electrical machines

Abstract: Core losses in rotating electrical machines have been estimated through direct use of the standard Epstein loss data of the employed magnetic laminations, without introducing empirical correcting factors. The prediction is based on a numerical finite element approach to magnetic flux distribution, coupled to a physical model of losses in ferromagnetic laminations under generic flux waveform, which takes into account the specific role of the hysteresis and classical and excess loss components. An application has been made to the case of a 7.5-kW four-pole induction motor under no-load conditions. The predicted core losses turn out to be about 20% lower than the measured ones, a fact which points to an appreciable contribution of the rotor cage Joule losses and to the detrimental role played in the material properties by the residual and applied stresses introduced by lamination punching and core assemblage. >

Selection of the flux reference for induction machine drives in the field weakening region

Abstract: In a conventional rotor flux oriented induction motor drive, the flux reference is usually made proportional to the inverse of the rotor speed for field weakening operation. The authors indicate, however, that such a variation cannot maintain optimal (maximum) torque capability maintain optimal (maximum) torque capability of the machine over the entire speed range. It is further shown that nearly optimal torque capability can be achieved in a stator flux oriented system when the stator flux reference is varied as the inverse of the rotor speed. >

Analysis of a concentrated winding induction machine for adjustable speed drive applications. II. Motor design and performance

Abstract: For pt.I. see ibid, vol.6, no.4, p.679-83 (1991). The performance of multiphase machines designed for operation with static power converters is described. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Fourier analysis is used for investigation of the effects of different air-gap-field spatial distributions and time harmonics in the supply. The approach to analysis of such machines, derived in Part I, is implemented by means of a digital-computer simulation. Compound results indicate that when operating in conjunction with a converter supply, a specially wound five-phase machine is theoretically capable of a 10% improvement in torque per root-mean-square ampere assuming the same peak air-gap-flux density level in the air gap of the machine as in a conventionally designed induction motor of the same rating. >

Computer aided detection of airgap eccentricity in operating three-phase induction motors, by Park's vector approach

Abstract: The subject of online detection of airgap eccentricity in three-phase induction motors is discussed, and a noninvasive approach, based on the computer-aided monitoring of the stator current Park's vector, is introduced. Experimental results, obtained by using a special fault producing test rig, demonstrate the effectiveness of the proposed technique, for detecting the presence of airgap eccentricity in operating three-phase induction machines. >

Integrated motor drive and recharge system

Abstract: A drive and recharge system is disclosed that includes a bidirectional dc power source, two voltage-fed inverters, two induction motors, and a control unit. In the drive mode, power is bidirectionally connected between the dc power source and the motors. In the recharge mode, single-phase power applied to the neutral ports of the two motors is converted with unity power factor to return energy to the dc power source. An alternate scheme is also presented which uses a single motor having two sets of windings.

A neural network approach to real-time condition monitoring of induction motors

Abstract: A neural network-based incipient fault detector for small and medium-size induction motors is developed. The detector avoids the problems associated with traditional incipient fault detection schemes by employing more readily available information such as rotor speed and stator current. The neural network design is evaluated in real time in the laboratory on a 3/4 hp permanent magnet induction motor. The results of this evaluation indicate that the neural-network-based incipient fault detector provides a satisfactory level of accuracy, greater than 95%, which is suitable for real-world applications. >

Vector-controlled induction motor drive with a self-commissioning scheme

Abstract: Different vector-controlled structures are discussed, and their suitability for an economical and reliable industrial drive system is explored. From this, the design of a compact control hardware is derived, composed of an 80196 microcontroller and an ASIC (application-specific integrated circuit) for the generation of the pulsewidth modulation (PWM) signals. The drive system can be configured from a host computer or a hand-held servicing unit through a serial data link. Monitoring and diagnostic functions are included. A self-commissioning scheme permits the setting of the parameters for optimum dynamic performance of the induction motor. Various oscillograms demonstrate the behavior of the vector controller operating a 25-kVA PWM inverter. >

Transient model of a doubly excited reluctance motor

Abstract: A transient machine model of a doubly fed reluctance motor is derived by means of winding function and d-q transformation theory. The machine consists of a double-wound stator with four and eight pole sets. The rotor is equipped with six poles. The machine, related to the Hunt motor, has the synchronous speed of a twelve-pole machine. Comparison of simulated results to test results indicates that the higher harmonics in the motor inductances are important for predicting the current waveform. >

Methodology for on-line incipient fault detection in single-phase squirrel-cage induction motors using artificial neural networks

Abstract: A novel approach for online detection of incipient faults in single-phase squirrel-cage induction motors through the use of artificial neural networks is presented. The online incipient fault detector is composed of two parts: (1) a disturbance and noise filter artificial neural network to filter out the transient measurements while retaining the steady-state measurements, and (2) a high-order incipient fault detection artificial neural network to detect incipient faults in single-phase squirrel-cage induction motors based on data collected from the motor. Simulation results show that neural networks yield satisfactory performance for online detection of incipient faults in single-phase squirrel-cage induction motors. The neural network fault detection methodology presented is not limited to single-phase squirrel-cage motors (used as a prototype), but can also be applied to many other types of rotating machines, with the appropriate modifications. >

Adjustable AC capacitor for a single phase induction motor

Abstract: The most common practice for starting a single-phase induction machine (SPIM) is to install a starting capacitor in series with the auxiliary winding. In some applications, two capacitors are used. One is used during the starting period to help create the starting torque. The other one is used during the running condition to improve efficiency. The possibility of using an electronic switch in parallel with the running capacitor, thereby providing the equivalent of a starting capacitor, is discussed. The capacitor is shorted during each cycle to vary the effective size of the AC capacitor. By using this method, only one capacitor is used for both the starting and running condition, and a starting performance similar to that of the conventional method using two capacitors can be obtained. >

Low-torque-ripple switched reluctance motors for direct-drive robotics

Abstract: A contender for direct-drive application, the switched reluctance motor, is examined. It is first described how the number of teeth on the rotor and stator can be selected to achieve an electromagnetic gearing, with the goal of eliminating the need for a mechanical gearbox. It is also discussed how the tooth arcs of the rotor and stator can be adjusted so as to reduce the torque ripple of the motor during commutation. The treatment of these subjects includes a detailed case study in which the performance of four related motors is compared using finite-element analysis with a commutation algorithm for torque control. It is discovered that, although a tradeoff exists between peak torque and torque ripple, the maximum smooth torque and minimum torque ripple can be achieved by the same direct-drive motor design. >

Iron losses in magnetic materials with six-step and PWM inverter supply (induction motors)

Abstract: The energetic behavior of two samples of soft magnetic materials fed by inverters has been studied. The authors dealt with the increase of the iron losses due to a nonconventional voltage supply. Six-step and PWM (pulse width modulated) inverter output voltages have been selected as the excitation waveforms for the samples under test. Extensive experimental results of high-quality grain-oriented silicon steel and amorphous-alloy-wound core samples are presented. A detailed description of the testing procedure is shown. The results are quite informative and quantify the iron-loss increase with nonsinusoidal supply in comparison with the results obtained by the standard tests (sinusoidal supply and Epstein method). The comparison can give useful indications to electromagnetic-device designers about the derating factors for the different magnetic materials that have to be used in designing devices fed by static power sources. >

A novel vector control scheme for transistor PWM inverter-fed induction motor drive

Abstract: A novel vector control scheme for a transistor pulse-width-modulation (PWM)-inverter-fed induction motor drive is presented. The system is based on a current control loop that consists of two independent nonlinear controllers that regulate the DC (field-oriented) components of the stator current vector. Three-level hysteresis comparators are used as current controllers. The outputs of the comparators select the appropriate inverter output voltage vectors via a switching erasable programmable ROM (EPROM) table. The theoretical principle of this method is discussed. Simulation and experimental results that illustrate the operation of the proposed system and performance in comparison with the other known schemes based on two-level hysteresis comparators are presented. >

Characteristics of a bearingless induction motor

Abstract: A bearingless induction motor with additional windings in the stator slots is proposed. Additional two-pole windings were wound with the conventional four-pole windings to produce radial magnetic forces. These forces, which control the position of the rotor shaft, are produced when magnetic fluxes from the two-pole windings cause an imbalance in the revolving magnetic field of the four-pole windings. Inductance functions were measured to derive the machine inductance matrix expression, and from this matrix the radial force and current relationships were found. Control circuits were designed and fabricated for a test machine. This test machine was successfully driven by the control circuits. A bearingless induction motor was successfully operated at speeds up to 6000 r/min. >

Robust speed control of IM with torque feedforward control

Abstract: The authors present a robust speed control of an induction motor (IM) using a load torque observer and feedforward control. The speed response characteristics using a conventional PI (proportional plus integral) controller are affected by variations of system parameters. With the proposed system, the load torque disturbance and the effects of motor and mechanical parameter variations can be removed. The entire control processing was performed by the software of a digital signal processor within a reasonable period, and experimental results showed the robustness of the control system against the disturbance torque and the variation of motor and mechanical parameters. >

Design and implementation of a fuzzy controller for a high performance induction motor drive

Abstract: A limit-cycle controlled induction motor drive with a fuzzy controller has been designed and implemented. The torque and flux of the proposed drive system are regulated by the limit-cycle control technique. It follows that very quick torque response can be achieved. Since the dynamic model of this type of drive system is not easy to obtain, a fuzzy controller was developed and used in the speed control feedback loop to obtain good dynamic rotor speed response. The fuzzy algorithms in the proposed controller are systematically found from intuition and experience about the drive systems. The experimental results indicate that good dynamic speed performance can be achieved by the proposed controller. Moreover, since the rotor parameters are not needed in the implementation of the drive system, and due to the inherent feature of high adaptive capability possessed by the fuzzy controller, the performance of the controller drive system is rather insensitive to the parameter and operating condition changes. >

Calculation of cage induction motor equivalent circuit parameters using finite elements

Abstract: A means by which the finite-element method can be used in conjunction with the conventional equivalent circuit model to determine the equivalent circuit components for a three-phase cage induction motor is described. The method uses separate finite-element models for the rotor and the stator, consisting of one slot pitch and one phase band, respectively. The use of minimal models leads to a fast execution time. The method is illustrated by comparing computer predictions of performance with test measurements made on four motors, ranging in size from 4 to 150 kW.

Simple efficiency maximizer for an adjustable frequency induction motor drive

Abstract: A new method of efficiency maximization that utilizes sensing of the third-harmonic component of air-gap flux is proposed. This signal is used to determine the resulting instantaneous position of the fundamental component of the air gap flux and, consequently, the torque- and flux-producing components of the stator current. In addition, the third harmonic signal is also used to determine the rotor speed. Hence, the output power of the machine can be calculated with only a single sensor wire attached to the neutral point of the machine. The flux-producing component can be readily adjusted to produce the minimum input power for a fixed amount of output power (fixed speed). >

Simulation of induction machine operation using a step by step finite element method coupled with circuits and mechanical equations

Abstract: The authors present the modeling of an induction machine using a nonlinear magnetodynamic complex method coupled with the circuit equations. The method is an extension to the harmonic solution of nonlinear magnetodynamic problems of the proposed classical finite element method. The coupling of the circuit equation completes the 2-D finite element method by making it possible to take into account the 3-D part of the motor. Another advantage is the ability to include voltage sources. >

Vector control of induction motor with fuzzy PI controller

Abstract: A description is presented of the fuzzy proportional-plus-integral controller for the vector control system of an induction motor, and the performance of the system using this controller is discussed. The theoretical process of the fuzzy inference and the guide to a design of the controller are presented. This controller is applied to the laboratory model drive system with 0.75 kW induction motor. The simulation results demonstrate the good performance of this system. >