Showing papers on "Transient (oscillation) published in 1998"

A modified direct torque control (DTC) for induction motor sensorless drive

Abstract: Direct torque control (DTC) is known to produce quick and robust response in AC drives. However, during steady state, notable torque, flux and current pulsations occur. They are reflected in speed estimation, speed response, and also in increased acoustical noise. This paper introduces a new direct torque and flux control based on space-vector modulation (DTC-SVM) for induction motor sensorless drives. It is able to reduce the acoustical noise, the torque, flux, current, and speed pulsations during steady state. The DTC transient merits are preserved, while better quality steady-state performance is produced in sensorless implementation for a wide speed range. The flux and torque estimator is presented and an improved voltage-current model speed observer is introduced. The proposed control topologies, simulations, implementation data, and test results with DTC and DTC-SVM are given and discussed. It is concluded that the proposed control topology produces better results for steady-state operation than the classical DTC.

Parameter identification of induction motor model using genetic algorithms

Abstract: The paper deals with methods of identification of the parameters of an induction motor model using genetic algorithms. It is supposed that the inverter supplying the motor is directly accessible for control of the conduction sequences of its power switches. This makes it possible to carry out a test consisting of a transient from standstill to steady-state operation at a given frequency and successive free motion to standstill. During this test, data are acquired referring to stator voltages, and currents and speed. Then, a genetic algorithm is employed with the aim of determining the mechanical and electrical parameters of the model, so as to reproduce the input-output behaviour of a real open-loop system.

Reflected wave modeling techniques for PWM AC motor drives

Abstract: Reflected wave transient voltages that are impressed on drive output cables and low voltage AC induction motors are simulated with an excitation source of steep fronted d/spl nu//dt pulse waveforms from a pulse width modulated (PWM) voltage source inverter. Motivation for system simulation arises from a need to correlate reflected wave peak voltage and risetime with the dielectric insulation capability of both motor and cable. Simulations based on an accurate system model also allow investigation into the effects of changing wire gauge, motor HP, cable distance or addition of drive output filters. System parameters of the inverter, cable and motor model are investigated in detail. Special emphasis is given to the importance of modeling cable skin and proximity effects. Simulation, measured lab and field results are compared. The main objective of the paper is to propose a reflected wave building block model that uses existing software on the market, is simple, computationally fast, easily configurable, reasonably accurate and allows investigation with wide variation of system parameters.

Properties of Amorphous Silicon and its Alloys

Abstract: An extensive collection of research papers on the properties, preparation and exploitation of amorphous silicon, which includes discussion of PECVD growth, transient and steady state photoconductivity, solar cells, photodetectors, LEDs, xerographic applications, and macroscopic data.

Three-dimensional wave-envelope elements of variable order for acoustic radiation and scattering. Part I. Formulation in the frequency domain

Abstract: A variable-order, infinite “wave-envelope” element scheme is formulated for transient, unbounded acoustical problems. The transient formulation which is local in space and time is obtained by applying an inverse Fourier transformation to a time-harmonic wave-envelope model whose formulation is described in a companion article. This procedure yields a coupled system of second-order differential equations which can be integrated in time to yield transient pressure histories at discrete nodal points. Far-field transient pressures can also be obtained at adjusted times. The method can be applied quite generally to two-dimensional and three-dimensional problems and is compatible with a conventional finite element model in the near field. The utility of the method is confirmed by the presentation of transient solutions for axisymmetric and fully three-dimensional test problems. An implicit time integration scheme is used and computed results are compared to analytic solutions and to solutions obtained from alternative numerical schemes. Close correspondence is demonstrated and the scheme is shown to be stable for the problems which are presented. CPU times for a large three-dimensional problem are shown to compare favorably with those required for an equivalent transient boundary element computation.

Complex representation in nonlinear time harmonic eddy current problems

Abstract: Several possibilities are presented to deal with nonlinearity in ferromagnetic media in the case of time harmonic excitation in steady state, without losing simplicity in describing the potentials by means of complex peak values. The main idea is to introduce a fictitious time independent and inhomogeneous material to take into account the nonlinear relationship between the field quantities. Four methods are shown and investigated on a 3D time harmonic eddy current problem, using the T,/spl Phi/-/spl Phi/ finite element formulation. The vector potential is represented by means of edge elements and the scalar potential by nodal elements. The results obtained are compared with transient computation.

Hybrid modelling of inhomogeneous transformer winding for very fast transient overvoltage studies

Abstract: This paper presents a novel approach for the modelling of transformer windings, which is valid in the frequency range of 10 kHz to a few MHz. It is a hybrid model; coil-by-coil detailed plus inter-coil black box model. The parameter estimation of the detailed model and the synthesis of the black box model is based on frequency domain measurements. The technique is applied to a high-voltage transformer winding. The comparison of the measurements and the frequency domain simulation of the model with EMTP confirms the validity and accuracy of the model for the intended frequency range. Experiments in the frequency range of several MHz reveal that remarkable overvoltages appear at the connecting point of the inverted and interleaved part of this winding. It is shown that the reason of the VFTO (very fast transient overvoltage) in the MHz range is the inhomogeneity of the winding parts.

Transient thermal analysis of induction motors

Abstract: Induction machines transient thermal analysis has been a subject of interest for electric machine designers in their effort to improve machine reliability and in rotor design optimisation. The study of transient thermal behavior is useful to identify causes of failure in induction machines. This paper presents a 2-D transient analysis of induction machines using the available heat transfer coefficients in literature. A generalised finite element code developed with Galerkin's weighted residual technique is used for analysis. The model is applied to one squirrel-cage totally-enclosed fan cooled machine of 3.7 kW and another surface cooled machine of 5.7 kW. The predicted temperatures compare well with test results. The advantages and limitations of this model are discussed.

VRM transient study and output filter design for future processors

Abstract: In this paper, the transient response of the (voltage regulator module) VRM output voltage when the processor has a fast load change is analyzed. The parasitic parameters play important roles in the transient. The system can be divided into several resonant loops. Each loop can be approximately considered as a decoupled second order system. The transient response is affected by the magnitude of the load change rather than the slew rate of it. Limitations of the present VRM topology for future specifications and output filter design are discussed.

AC-DC Power System Analysis

Abstract: * Chapter 1: Introduction * Chapter 2: The AC-DC converter in steady state * Chapter 3: The power flow solution * Chapter 4: The harmonic solution * Chapter 5: Three-phase power and harmonic flow * Chapter 6: Electromagnetic transient simulation * Chapter 7: Electromechanical stability * Chapter 8: Electromechanical stability withtransient converter simulation * Appendices

Development of Grounded Electrical Source Airborne Transient EM (GREATEM)

Abstract: We describe a new airborne EM system which uses a grounded electrical source and an airborne magnetic field receiver to increase the depth of investigation. Using a grounded source, we can apply a ...

Power system frequency estimation

Abstract: A new algorithm of power system frequency estimation is presented. The algorithm applies orthogonal signal components obtained with use of two orthogonal FIR filters. The essential property of the algorithm presented is its outstanding immunity to both signal orthogonal component magnitudes and FIR filter gains variations which ensures 1.5 mHz accuracy of estimation over typical (±2 Hz) range of measured frequency deviation. The results of the algorithm simulation tests using the EMTP software package are also included. It was confirmed that the algorithm dynamics are good enough to track power system frequency even under transient conditions.

Combined transient and dynamic analysis of HVDC and FACTS systems

Abstract: A new approach to HVDC and FACTS transient/dynamic simulation based on an interactive execution of an AC transient stability program (TSP) and the Electromagnetic Transients Program (EMTP) is described. Through the integration of the detailed transient model of FACTS with the transient stability program, authentic simulation is achieved without simplifications. Both HVDC and thyristor controlled series capacitor (TCSC) systems are used to validate the approach, under different coupling situations between both TSP and EMTP.

A simple method of transient electromagnetic data analysis

Abstract: Time-domain or transient electromagnetic (TEM) methods are used routinely in environmental, hydrogeological, energy, and mineral resources investigations owing to their ease of use and ability to generate diagnostic data. In some typical field situations, the gross structure of the subsurface may be approximately 1-D, so 1-D interpretation schemes can be used to retrieve an interpretive model for the depth soundings.

Augmentation of transient stability using a superconducting coil and adaptive nonlinear control

Abstract: The very nonlinear nature of the generator and system behaviour following a severe disturbance precludes the use of classical linear control techniques. In this paper, a nonlinear adaptive excitation and a thyristor-controlled superconducting magnetic energy storage (SMES) unit is proposed to enhance the transient stability of a power system with unknown or varying parameters like equivalent reactances of the transmission lines. The SMES unit is located near the generator bus terminal in a power system. A nonlinear feedback control law is found which linearizes and decouples the power system. An adaptive control law is used to design the controller for the generator excitation and SMES system. Simulation results demonstrate that the proposed controller can ensure transient stability of a single-machine-infinite-bus system under a large sudden fault which may occur near the generator bus terminal.

Method and apparatus for multi-function electronic motor protection

Abstract: A multi-function protection system (8) for protecting electrical equipment such as a screw compressor motor is shown having a housing (10, 20) mounting current sensing toroids (CT1, CT2, CT3) and associated circuitry as well as associated circuitry for temperature sensing PTC resistors (S1, S2, S3) adapted to be placed in heat conductive relation with respective windings of the motor. The circuitry is connected to an analog-to-digital converter or ADC (U6) which provides a binary coded input to a micro-controller (U5). The micro-controller performs protection sub-routines to control an output switch (Q4) which in turn controls the state of energization of a relay (K1) coupled to the screw compressor motor. The circuitry includes a current unbalance section (30a, 30b), an over temperature section (32), a low voltage cut-out circuit (33), a current transducer section (35), a signal conditioning circuit (36a, 36b, 36c), a micro-controller section (40) incorporating a shorted sensor protection system, current overload calibration section (41) and fault diagnostic section (42). A fault bank routine filters transient voltages resulting from industrial or environmental electromagnetic interference (EMI) for current overload, current imbalance and over temperature transient voltages to distinguish real fault conditions from EMI transients.

Calibration of electrodiffusion friction probes using a voltage-step transient

Abstract: Voltage-step transient experiments are used to calibrate electrodiffusion (ED) friction probes. The approach is demonstrated on the probes in high-speed rotating impellers. This calibration has shown that shear rates as high as 106s-1 can be measured reliably using 0.5mm Pt working electrodes in ferro/ferricyanide aqueous solutions. The complete transient calibration experiment provides sufficient information about the dynamics of ED friction probes.

Transient temperature measurement using embedded thermocouples

Abstract: The response time of thermocouples is generally considered to be a limiting factor when transient temperature changes need to be assessed in solids. As an example, transient temperature changes which develop during dynamic straining of materials, adiabatic shear band formation, dynamic fracture and related fields are often investigated using sophisticated noncontact measurement techniques such as infrared detectors. In these phenomena, the time scale is of the order of the microsecond. In this paper, the authors revisit the application of thermocouples to such measurements using small embedded thermocouples (ETC). Experiments with dynamically loaded polymeric disks (characteristic strain rate of 103 s−1) show that the thermocouples record transient temperatures with a short typical rise time of 10 μs as a result of the conversion of plastic deformation into heat. This observation is corroborated by the solution of the temperature distribution in a sphere subject to constant surface temperature which predicts the same fast reaction. Specifically, considering a sphere which is representative of the sensing bead, the average temperature is shown to rise in a few microseconds. These theoretical results can be used to deconvolve the experimental results with respect to a calculated impulse response of the sensor to recover the actual temperature variations. The results show that small thermocouples can be embedded to yield useful information about the transient temperature evolution in a solid. This technique is easy to use and provides an important complement to other noncontact techniques.

Transient Thermal Effects of Radiant Energy in Translucent Materials

Abstract: When a solid or stationary fluid is translucent, energy can be transferred internally by radiation in addition to heat conduction. Since radiant propagation is very rapid, it can provide energy within a material more quickly than diffusion by heat conduction. Radiation emitted in a hot material can also be distributed rapidly in the interior. The result is that transient temperature responses including radiation can be significantly different from those by conduction alone. This is important for evaluating the thermal performance of translucent materials that are at elevated temperatures, are in high temperature surroundings, or are subjected to large incident radiation. Detailed transient solutions are necessary to examine heat transfer for forming and tempering of glass windows, evaluating ceramic components and thermal protection coatings, studying highly backscattering heat shields for atmospheric reentry, porous ceramic insulation systems, ignition and flame spread for translucent plastics, removal of ice layers, and other scientific and engineering applications involving heating and forming of optical materials. Radiation effects have been studied less for transients than for steady state because of the additional mathematical and computational complexities, but an appreciable literature has gradually developed. This paper will review the applications, types of conditions, and geometries that have been studied. Results from the literature are used to illustrate typical radiation effects on transient temperatures, and comparisons are made of transient measurements with numerical solutions.

An analysis/synthesis tool for transient signals that allows a flexible sines+transients+noise model for audio

Abstract: We present a flexible analysis/synthesis tool for transient signals that extends current sinusoidal and sines+noise models for audio to sines+transients+noise. The explicit handling of transients provides a more realistic and robust signal model. Because the transient model presented is the frequency domain dual to sinusoidal modeling, it has similar flexibility and allows for a wide range of transformations on the parameterized signal. In addition, due to this duality, a major portion of the transient model is sinusoidal modeling performed in the frequency domain. In order to make the transient and sinusoidal models work more effectively together, we present a formulation of sinusoidal modeling (and therefore transient modeling) in terms of matching pursuits and overlap-add synthesis. This formulation provides a tight coupling between the sines+transients+noise model because it allows a simple heuristic, based on tonality, as to when an audio signal should be modeled as sines and/or transients and/or noise.

Multi-Category Classification of Tool Conditions Using Wavelet Packets and ART2 Network

Abstract: This paper proposes a new approach for multi-category identification of turning tool conditions. It uses the time-frequency feature information of the AE signal obtained from best-basis wavelet packet analysis. By applying the philosophy of divide-and-conquer and a local wavelet packet extraction technique, acoustic emission (AE) signals from turning process have been separated into transient and continuous components. The transient and continuous AE components are used respectively for transient tool conditions and tool wear identification. For transient tool condition identification, a 16-element feature vector derived from the frequency band value of wavelet packet coefficients in the time-frequency phase plane is used to identify tool fracture, chipping and chip breakage through an ART2 network. To identify tool wear status, spectral and statistical analysis techniques have been employed to extract three primary features: the frequency band power at 300 kHz –600 kHz , the skew and kurtosis. The mean and standard deviation within a moving window of the primary features are then computed to give three secondary features. The six features form the inputs to an ART2 neural network to identify fresh and worn state of the tool. Cutting experimental results have shown that this approach is highly successful in identifying both the transient and progressive tool wear states over a wide range of turning conditions.