Showing papers on "Induction motor published in 1987"

Waveform Distortion and Correction Circuit for PWM Inverters with Switching Lag-Times

Abstract: The switching lag-time that prevents the phase shortage of inverter arms causes serious waveform distortions and fundamental voltage drops in pulsewidth-modulated inverter output. Distortions in the PWM inverter-fed induction motor system over the various frequencies of the carrier are investigated and a correction circuit with PWM potential feedback is proposed; the effectiveness of that circuit is shown by experiments.

Study of Parameter Sensitivity in High-Performance Inverter-Fed Induction Motor Drive Systems

Abstract: Vector control schemes are used in inverter-fed induction motor drives to obtain high performance. Crucial to the success of the vector control scheme is the knowledge of the instantaneous position of the rotor flux. The position of the rotor flux is measured in the direct scheme and estimated in the indirect schemes. Since the estimation of the flux position requires a priori knowledge of the induction motor parameters, the indirect schemes are all machine-parameter dependent. Changes in temperature and saturation levels of the machine vary the machine parameters and, hence, indirectly influence both the steady state and the dynamic operation of the drive system. Analytic expressions are derived to evaluate the effects due to parameter sensitivity. The simulation is experimentally verified on a drive system.

Secondary Resistance Identification of an Induction-Motor Applied Model Reference Adaptive System and Its Characteristics

Abstract: Induction-motor torque is not accurately controlled when the estimated secondary resistance of an induction-motor model in a vector controller differs from the true secondary resistance. An algorithm which identifies the secondary resistance on-line is developed. The motor operating condition for secondary resistance identification, the stable identifier organization, and the experimental investigation confirming the identification algorithm performance are presented. The algorithm is based on the theory of model reference adaptive systems (MRAS). The proposed algorithm stably identifies the secondary resistance under any load and any speed when a sinusoidal signal is injected into the flux axis primary current. The vector controller adopting this algorithm controls motor torque accurately under any load and any speed.

Optimal Efficiency Control of an Induction Motor Drive

Abstract: This paper describes a practical method for achieving optimal efficiency over the complete operating range of a variable speed drive. The proposed system adaptively adjusts the flux level in the motor based upon a direct measurement of the power input to the drive. An internal field orientation torque control loop and a speed regulator are employed to maintain the load speed requirements. Experimental results describing the efficiency optimization and the dynamic behavior of the drive at reduced flux are presented. The influence of the tuning of the field oriented controller on the efficiency of the drive is experimentally investigated.

Axial-Field Electrical Machines - Design and Applications

Abstract: Axial-field electrical machines (AFM's) offer an alternative to the conventional radial-field machines (RFM's). In the axial-field machine, the airgap flux is axial in direction and the active current-carrying conductors are radially positioned. This paper presents the design characteristics, special features, manufacturing aspects, and potential applications for axial-field electrical machines. The experimental results from several prototypes, including de machines, synchronous machines, and single-phase machines are given. The special features of the axial-field machine, such as its planar and adjustable airgap, flat shape, ease of diversification, etc., enable axial-field machines to have distinct advantages over conventional machines in certain applications, especially in special purpose applications.

The analysis of fields and torques in spherical induction motors

Abstract: The advent of robotics and automated manufacturing processes has brought about an urgent need for novel electromechanical transducers with unusual design and performance characteristics. Operating flexibility, ruggedness, size, force-to-weight ratio, and robust control capabilities are design attributes which place a heavy burden on conventional machines used for manipulation purposes. The spherical induction motor is an electromechanical drive which holds considerable promise in these application areas. A general analysis of both the fields and resultant forces generic to the spherical induction motor is presented. The analysis properly accounts for the diffusion of the magnetic field with changing frequency and motor speed. To aid in the prediction and conceptualization of the torque and commensurate motor losses, normalized plots of these parameters are given for various limiting values of skin depth ratio to conductor thickness. Results indicate that the device is capable of continuous speed control and efficient torque production.

Performance of Feedforward Current Regulators for Field-Oriented Induction Machine Controllers

Abstract: To achieve instantaneous control of induction motor torque using field-orientation techniques, it is necessary that the phase currents be controlled to maintain precise instantaneous relationships Failure to do so results in a noticeable degradation in torque response Most of the currently used approaches to achieve this control employ classical control strategies which are only correct for steady-state conditions A modern control theory approach which circumvents these limitations is developed The approach uses a state-variable feedback control model of the field-oriented induction machine This state-variable controller is shown to be intrinsically more robust than PI regulators Experimental verification of the performance of this state-variable control strategy in achieving current-loop performance and torque control at high operating speeds is included

Field orientation control of a permanent magnet motor

Abstract: A field orientation control system for an interior permanent magnet synchronous motor includes function generating means responsive to a torque command signal for producing direct and quadrature axis direct current signals which are converted to synchronously-varying two-phase signals for coupling to power control means, for effecting sinusoidal energization of the permanent magnet motor. The function generators modify the torque command signal as a predetermined function of the motor parameters. Rotor position information is derived from measured stator voltages and currents without the use of a separate rotor position sensor. The control system includes means for establishing a preselected amplitude of a stator α-axis current in the motor at start-up prior to establishing orthogonal β-axis current such that the motor rotor is caused to become initially aligned with the selected α-axis.

A Current Source GTO Inverter with Sinusoidal Inputs and Outputs

Abstract: With the application of gate turn-off thyristors (GTO's) and PWM control techniques, a current source inverter capable of producing sinusoidal input/output (I/O) voltages and currents has been developed. The sinusoidally modulated current is fed to the GTO's in the rectifier and inverter sections. The overvoltage-absorption capacitors connected to the ac input and output terminals function as a filter and, consequently, the waveforms of the input/output voltages and currents become sinusoidal. Because the PWM control utilizes the high-speed switching characteristics of the GTO's, the dc link current smoothing reactor and the overvoltage absorption capacitors are greatly reduced. The dc link voltage in the rectifier section is controlled to adjust the ac motor current. This is accomplished by using the firing angle shift method in conjunction with the method involving varying the width of the bypass gate pulses, which put the rectifier section into a bypass state. The current source GTO inverter is used to drive an 11-kW induction motor. As a result, excellent acceleration and deceleration characteristics are obtained, which verifies that the new current source inverter is quite suitable for driving an ac motor at variable speeds.

Method of induction motor control and electric drive realizing this method

Abstract: Method of induction motor vector control in Cartesian and polar coordinates, whereby control of the rotor speed, induction motor torque, as well as dynamic, power, and thermal processes, which is interconnected with control of the rotor flux linkage amplitude and phase as functions of the desired induction motor torque, is achieved in an electric drive by synchronizing the stator current control by a controlled synchronization frequency by means of three control inputs, one control input is used to control the synchronization frequency and phase as functions of the desired rotor torque and speed; two other control inputs are used to control the amplitudes of ortho-phasal and current phase to a phase angle equal to the ratio of the ortho-phasal and co-phasal and ortho-phasal currents as functions of the desired induction motor torque, the actual desired amplitude of the rotor flux linkage, and magnetizing characteristic of the induction motor, while the amplitudes of the ortho-phasal and co-phasal currents is kept mostly equal, the synchronization phase being additionally controlled as a function of the induction motor temperature. An apparatus is described to carry out the method.

Performance Optimization of Induction Motor-Pump System Using Photovoltaic Energy Source

Abstract: The optimization of a photovoltaic pumping system based on an induction motor driven pump that is powered by a solar array is presented in this paper. The motor-pump subsystem is analyzed from the point of view of optimizing the power requirement of the induction motor, which has led to an optimum u-f relationship useful in controlling the motor. The complete pumping system is implemented using a dc-dc converter, a three-phase inverter, and an induction motor-pump set. The dc-dc converter is used as a power conditioner and its duty cycle is controlled so as to match the load to the array. A microprocessor-based controller is used to carry out the load-matching.

Aggregation of Induction Motors for Transient Stability Load Modeling

Abstract: An investigation of several methods for aggregating induction motors is described. The accuracy of the methods is compared using frequency-domain techniques. A new method involving the use of one or two aggregate motors is described and shown to be superior to other methods.

A New Longitudinal End Effect Factor for Linear Induction Motors

Abstract: The longitudinal end effect in a linear induction motor (LIM) is analysed assuming two travelling magnetic flux density waves in the airgap: the wave travelling with synchronous velocity and the wave representing end effect [1]. A simple equation for the end effect factor which modifies the airgap EMF is obtained, and a simple equivalent circuit incorporating the end effect factor is established. Analysis is compared with measurements from two largescale single-sided LIM's. The equation for the end effect factor is sufficiently accurate to be used for design studies of LIMs. Since end effects are negligible at low speeds, the end effect factor has application for medium and high-speed LIMs.

Induction Machine Modelling for Electromagnetic Transient Program

Abstract: A method is presented by which an accurate dynamic induction motor model may be developed from a knowledge of standard specification data for the motor. The incorporation of the model into the Electromagnetic Transients Program (EMTP) is described. Examples are given of its use in the study of the starting performance of a large induction motor and of the response of the same motor following various electrical faults.

Calculation of the flux density and the unbalanced pull in two pole induction machines

Abstract: In this paper, the relationship between the homopolar flux generated by a statically eccentric rotor and the unbalanced magnetic pull in two-pole induction motors is considered. We will show that due to this kind of eccentricity, a homopolar flux is generated having the supply frequency, yielding a vibrational component of the unbalanced magnetic pull with the double supply frequency.

Rotor fault detector for induction motors

Abstract: A method and apparatus for detecting rotor faults in an induction motor. A flux sensor generates a flux signal corresponding to the magnetic flux at a predefined flux detection point external to the motor. A current sensor generates a current signal proportional to the current drawn by said motor. A time series of data points is stored, representing the values of the flux signal and the current signal over a period of time. The time series are transformed by FFT into a set of flux spectra and into a set of current spectra. Then the line frequency of the motor's power supply is determined by finding the maximum of the current spectra. Similarly, the slip frequency of the motor is determined by finding the maximum of the flux spectra in a predefined spectral range (e.g., below 2 Hz). The analysis of the rotor is then performed by comparing the amplitude of the current spectra, at a set of rotor fault harmonic frequencies, with specified fault threshold criteria. Each rotor fault harmonic frequency is a predefined function of the line frequency and the slip frequency. The presence of a rotor fault is denoted if the amplitude of any of said current spectra exceed a corresponding fault threshold criteria.

Optimization of Three-Phase Induction Motor Design Part I: Formulation of the Optimization Technique

Abstract: This two-part paper deals with the optimization of the induction motor designs with respect to cost and efficiency. Most studies on the design of an induction motor using optimization techniques are concerned with the minimization of the motor cost and describe the optimization technique that was employed, giving the results of a single (or several) optimal design(s). In the present paper, a more comprehensive study on the optimization of a three-phase induction motor design was performed. This includes the relationship between motor cost, efficiency, and power factor; the effect of the properties of the electrical steel; and other effects as they occur in an optimal design. In addition, the optimization procedure that was used in this paper includes a design program, where some of the secondary parameters (which are called here variable constants), are modified according to the optimal results, in contrast to other studies where these parameters remain constant for the entire optimization. In this part, a new mathematical formulation of the optimization problem of the induction motor is presented.

Switched-Reluctance Motor Torque Characteristics: Finite-Element Analysis and Test Results

Abstract: The switched-reluctance motor is a simple and robust machine which is finding application over a wide power and speed range. To properly evaluate the motor design and performance and the effectiveness of different control schemes, an accurate model is required. The finite-element method can be used to predict the performance of the switched-reluctance motor as it can account for the salient pole geometry of the stator and rotor and the nonlinear properties of the magnetic materials. The computed results are shown to compare favorably with test results from a 7.5-kW Oulton switched-reluctance motor.

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

Abstract: The new "Direct Self-Control" (DSC) is a simple method of signal processing, which gives converter fed three-phase machines an excellent dynamic performance. To control the torque e.g. of an induction motor it is sufficient to process the measured signals of the stator currents and the total flux linkages only. Optimal performance of drive systems is accomplished in steady state as well as under transient conditions by combination of several two limits controls. The expenses are less than in the case of proposed predictive control systems or FAM, if the converters switching frequency has to be kept minimal.

Method of making an electric motor

Abstract: A method of making an electric motor with the stator winding inside a slotless cylindrical stator shell.

Variable speed controlled induction motor

Abstract: This invention relates to a variable speed control­led induction motor. The motor has a rotor (8) formed in one-piece and a plurality of stators (24,25), the rotor having a plurality of rotor cores (2,3) and a plurality of conductive members (5) interconnected and the stators having respective stator windings (22,23). The stator windings (22,23) are connected in series, the conductive members (5) are short-circuited by connecting members (r) at an air space or a non-magnetic core portion disposed between the rotor cores (2,3) and at least one of the plurality of stators (24,25) is associated with a phase shifter (38;47;50;51) providing the voltage of a given phase to the stator windings, whereby the rotational speed can be controlled easily over a wide range with the excellent torque characteristics and efficiency being maintained.

Influence of unbalanced magnetic pull on the radial stability of flexible-shaft induction machines

Abstract: An accurate assessment of the critical speed and the electromechanical damping is necessary to avoid the possibility of excessive vibrations and damage under operating conditions. Nowadays these problems are even more important, as the speed of induction motors may be varied using static inverters. 2-pole machines are very interesting when used with these inverters, because, f or a given frequency range of the inverter, the absolute speed range covered is twice the range of a 4-pole machine. Therefore the unbalanced magnetic pull and its relationship with the homopolar flux is analysed.

Efficient Operation of Surface-Mounted PM Synchronous Motors

Abstract: The steady-state performance of the surface magnet PM synchronous motor can be modeled to a good approximation by a simple equivalent circuit that includes the effect of the stator core loss. For operation at constant power with no restrictions placed on voltage or frequency, this model shows that there exists a unique operating point that yields the maximum efficiency and that the efficiency at this point is a function solely of the motor loss parameters, independent of the particular power level. Loss contour plots are introduced to show the existence of the optimum point and to show the nature of the losses as one departs from the optimum. The impact of these results on different operating modes for the machine is discussed. Test results are presented to verify that the optimal efficiency point exists and that the simple model predicts the machine performance reasonably well.

Double-Winding Rotary-Linear Induction Motor

Abstract: A rotary-linear induction motor whose stator possesses two windings generating the rotating and travelling fields is described. A theoretical analysis of the magnetic field and motor performance takes into account finite stator length effects. Computational results are partially verified by experimental measurements of the motor's model.

Analysis of the Audible Noise of Three-Phase Squirrel-Cage Induction Motors Supplied by Inverters

Abstract: One of the major problems in inverter-fed motors is the high level of audible noise produced by harmonic current and voltage components To analyze these phenomena the field in the machine airgap is calculated using the rotating field theory together with the Maxwell stress theorem This analysis yields a way for predicting the spectrum components produced by the motor and for relating it to the airgap flux density distribution time harmonics caused by the nonsinusoidal supply The theoretical approach is used for calculating the airgap flux density distribution and the frequency spectrum components of a small three-phase squirrel-cage induction motor fed by a six-step voltage source inverter (VSI) and by a pulsewidth-modulated (PWM) inverter The theoretical results are compared with experiments

Single and polyphase electromagnetic induction machines having regulated polar magnetic symmetry

Abstract: An induction motor includes a stator having at least one pair of stator windings and a rotor with rotor windings which are magnetically coupled to the stator windings via a circumferential air gap. The rotor windings are connected together in a squirrel cage or a wound rotor configuration. The stator windings are connected in series across the source. A capacitor is connected in parallel with one of the stator windings and this combination is connected in series with the other stator winding and is sized to form a quasi-double-resonant circuit, i.e., a quasi-parallel resonant circuit with the one winding and a quasi-series resonant circuit with the other winding. The stator windings are then grouped to form definite polar areas in the stator and a balanced rotating magnetic field is produced by all the windings throughout the entire load range when the motor is connected to a power source. Both a single-phase and a polyphase motor can be configured as a quasi-double-resonant circuit with respect to each input power phase. A further polyphase motor is also described with primary stator windings connected to each power phase input and interleaved secondary stator winding magnetically coupled to the primary stator windings but not directly connected to the power inputs. The secondary stator windings have capacitors coupled in parallel thereto to form parallel floating resonant circuits. In all of these motors, the power factor is in the range of 0.96 to 1.00, but normally closer to unity due to the resonant behavior of the circuitry. The induction motor can be driven above synchronous speed to act as a generator. Also, a method of generating torque is described.

Driving system for single phase A-C induction motor

Abstract: By employing a single phase pulse width modulated inverter system, a-c power line voltage may be effectively converted to single phase, variable amplitude and frequency sinusoidal voltage for driving a single phase a-c induction motor at an adjustable speed. The motor may be driven directly in response to the power line voltage (such as during start-up or when it is desired to run the motor at the power line frequency) by bypassing the inverter system and connecting the motor across the power line. Reduced energy consumption may be obtained by operating the motor in response to a reduced inverter output frequency. Switching the motor from the power line to the inverter, and vice versa, is accomplished without interruption. Immediately prior to each, switchover the inverter output voltage is synchronized to the power line voltage to minimize any electrical disturbance during the switching transition.

Power electronics and motor control

Abstract: Preface to second edition Preface to first edition List of principal symbols 1. Power switching theory 2. Switching devices and control electrode requirements 3. System realisation 4. Adjustable speed drives 5. DC motor control using a DC chopper 6. Controlled bridge rectifiers with DC motor load 7. Three-phase naturally-commutated bridge circuit as rectifier or inverter 8. Single-phase voltage controllers 9. Three-phase induction motor with constant frequency supply 10. Induction motor slip energy recovery 11. Induction motor speed control by the use of Adjustable-Voltage, Adjustable-Frequency, Step-Wave Inverters 12. Induction motor speed control by the use of adjustable frequency PWM inverters Appendix: General expressions for Fourier series Answers to problems References and Bibliography Index.