Showing papers on "Transient (oscillation) published in 1992"

Electrical machines and drives : a space-vector theory approach

Abstract: Introduction The space-vector method Steady-state and transient operation of induction machines and induction motor drives Steady-state and transient operation of synchronous machines and synchronous motor drives Steady-state and transient operation of DC machines and DC motor drives References and further reading Index.

A new fault location technique for two- and three-terminal lines

Abstract: A method for the computation of fault location in two- and three-terminal high voltage lines is presented. It is based on digital computation of the three-phase current and voltage 60/50 Hz phasors at the line terminals. The method is independent of fault type and insensitive to source impedance variation or fault resistance. Furthermore, it considers the synchronization errors in sampling the current and voltage waveforms at the different line terminals. The method can be used online following the operation of digital relays or offline using data transferred to a central processor from digital transient recording apparatus. The authors start with a two-terminal line to explain the principles and then present the technique for a three-terminal line. The technique was first tested using data obtained from a steady-state fault analysis program to evaluate the convergence, observability, and uniqueness of the solution. The technique was then tested using EMPT-generated transient data. The test results show the high accuracy of the technique. >

Transient Liquid Phase Bonding

Abstract: Transient liquid phase (TLP) bonding is a joining process that has been applied to many metallic systems throughout the ages, and yet it still holds promise as a technique for joining in aerospace and semiconductor applications. The TLP process produces a strong, interface-free joint with no remnant of the bonding agent. It differs from diffusion bonding in that the formation of a thin liquid interlayer eliminates the need for a high bonding or clamping force. The interlayer can be provided by foils, electroplate, sputter coats, or any other process that deposits a thin film on the faying surfaces. A schematic illustration of the process, shown in Figure 1, indicates that by placing a thin interlayer of an alloying metal containing a melting point depressant (MPD) between the two pieces of parent metal to be joined and heating the entire assembly, a liquid interlayer is formed. The liquid may form because the melting point of the interlayer has been exceeded, or because reaction with the parent metal results in a low melting liquid alloy. The liquid then fills voids formed by unevenness of the mating

Transient Stability Test Systems for Direct Stability Methods

Abstract: The aim of this paper is to present a standard set of power system data with benchmark results against which direct stability techniques to assess transient stability could be compared and tested. The test systems have been selected to display a wide range of dynamic characteristics to provide a robust test of the efficacy and accuracy of the various analytical techniques to analyze transient stability. Transient stability test system data and benchmark results obtained from two commercially available time domain stability analysis packages are presented in this paper.

A novel control scheme of a parallel current-controlled PWM inverter

Abstract: A parallel technique for current-controlled pulse-width-modulated (PWM) inverters is described. Two voltage source inverters, the output terminals of which are connected in parallel through current balancers, are used as a main circuit. In this scheme, excellent characteristics both in steady states and in transient states are obtained, keeping the average values of the cross current and zero sequence current at zero level. This current control scheme is applicable to large-capacity GTO inverters because good performance is attained even if the switching frequency is only a few hundred hertz, as is shown in the experimental results. >

A computer program (MODFLOWP) for estimating parameters of a transient, three-dimensional ground-water flow model using nonlinear regression

Abstract: This report documents a new version of the U.S. Geological Survey modular, three-dimensional, finite-difference, ground-water flow model (MODFLOW) which, with the new Parameter-Estimation Package that also is documented in this report, can be used to estimate parameters by nonlinear regression. The new version of MODFLOW is called MODFLOWP (pronounced MOD-FLOW*P), and functions nearly identically to MODFLOW when the ParameterEstimation Package is not used. Parameters are estimated by minimizing a weighted least-squares objective function by the modified Gauss-Newton method or by a conjugate-direction method. Parameters used to calculate the following MODFLOW model inputs can be estimated: Transmissivity and storage coefficient of confined layers; hydraulic conductivity and specific yield of unconfined layers; vertical leakance; vertical anisotropy (used to calculate vertical leakance); horizontal anisotropy; hydraulic conductance of the River, Streamflow-Routing, General-Head Boundary, and Drain Packages; areal recharge rates; maximum evapotranspiration; pumpage rates; and the hydraulic head at constant-head boundaries. Any spatial variation in parameters can be defined by the user. Data used to estimate parameters can include existing independent estimates of parameter values, observed hydraulic heads or temporal changes in hydraulic heads, and observed gains and losses along head-dependent boundaries (such as streams). Model output includes statistics for analyzing the parameter estimates and the model; these statistics can be used to quantify the reliability of the resulting model, to suggest changes in model construction, and to compare results of models constructed in different ways.

Variable-structure facts controllers for power system transient stability

Abstract: Nonlinear, variable-structure control theory is employed for series capacitor control and braking resistor control to improve the transient stability of a single machine infinite-bus (SMIB) system. A related simulation showed that variable-structure control of the series capacitor (SC) and braking resistor is effective for enhancement of power system steady-state performance and transient stability. Good transient response and high transmission limits were obtained. For the idealized control, only two switching applications are required, which suggests that the controller will be easily realized and reliable. The research reported suggests that variable-structure control can be used effectively for transient stability control of power systems. >

Efficient calculation of transient flow in simple pipe networks

Abstract: Extensions to the conventional method of characteristics allow transient conditions in simple pipe networks to be efficiently calculated. In particular, treating both boundary conditions and network topology in a general and comprehensive fashion simplifies the solution of many combinations of hydraulic devices. The algebraic framework presented includes a flexible integration of the friction loss term that reduces to previous linear approximations as special cases. In addition, an explicit algorithm is derived for a general hydraulic element called an external energy dissipator. This boundary condition conveniently represents surge tanks, relief valves, storage reservoirs, valves discharging to the atmosphere, and many other common devices. Significantly, the solution remains explicit even if friction losses and inertia effects are present in both the storage element and a connecting pipe. This comprehensive approach to transient analysis simplifies control logic, encourages accurate reporting of field data, and improves execution times. The procedure is illustrated by analyzing transient conditions in a small network containing a variety of devices.

Robust nonlinear controller design for transient stability enhancement of power systems

Abstract: A robust DFL (direct feedback linearization) nonlinear excitation controller is proposed to enhance transient stability for power systems. A robust control technique for linear systems is extended to design this controller. The design of the controller is independent of the operating point. Simulation results show that the controller has the following advantages: the fault location does not need to be known and the controller can overcome the variation of the reactance of the transmission line. Both transient stability enhancement and voltage regulation can be achieved. >

Transient response of a peak voltage detector for sinusoidal signals

Abstract: A fast peak detector for constant frequency sinusoidal signals is proposed. This detector is based on the concept of the orthogonal function set. The theoretical response time of this detector is less than one-fourth of a cycle. When this detector is used, the transient response of the output voltage is different under different inception angles. The mathematical equations to describe transient phenomena are derived and simulated. Because its transient response performance is superior to the conventional sinusoidal amplitude detector used in an analog controller, it can improve the transient response performance of the controller. For practical applications, the effects of harmonics and frequency variation are also discussed, simulated, and tested. >

Probabilistic Reactor Dynamics—II: A Monte Carlo Study of a Fast Reactor Transient

Abstract: The concept of how probabilistic reactor dynamics applies to a realistic problem, an accidental transient of the primary side of a fast reactor, is demonstrated. A full description of the reactor m...

Temperature surges in current-limiting circuit devices

Abstract: This paper studies the problem of heat transfer in a thermistor, which is used as a switching device in electronic circuits. The temperature field is coupled to the current flow by ohmic heating in the device, and the problem is rendered highly nonlinear by a very rapid variation of electrical conductivity with temperature. Approximate methods based on high activation energy asymptotics are developed to describe the transient heat flow, which occurs when the circuit is switched on. In particular, it is found that a transient “surge” phenomenon (akin to thermal runaway, but self-saturating) occurs, and we conjecture that this phenomenon may be associated with cracking of thermistors, which sometimes occurs during operation.

The trajectory tracking approach-a new method for minimum distortion PWM in dynamic high-power drives

Abstract: Feedforward pulsewidth modulators generate volt/spl middot/second differences between the controlling reference signal and the switched output waveform during transient operation. This dynamic modulation error is particularly pronounced at low switching frequency, e.g. with modern high-power GTO inverters. The compensation of this error is a key requirement when designing an optimal pulsewidth modulator for these applications. The trajectory tracking approach uses the steady-state trajectories of the current vector, computed from the optimal switching sequences, as templates. A tracking controller counteracts if the actual current vector deviates from this given path at transient operation. A decomposition of the current vector trajectory into its components enables, in addition, the identification of the instantaneous fundamental current, permitting the implementation of a fast current control system. Oscillograms from a 30 kW model induction motor drive demonstrate the high quality in terms of dynamic performance and minimum harmonic distortion obtained with a three-level inverter at only 200 Hz switching frequency. >

Transient simulation of arbitrary nonuniform interconnection structures characterized by scattering parameters

Abstract: A noniterative time-dependent circuit model is presented for transient analysis of general uniform and nonuniform interconnection structures terminated with arbitrary, linear or nonlinear loads. Simulated or measured scattering parameter data are used to characterize the interconnection structures. No approximations or model fitting are required. At each point in time, all coupled ports of the interconnection structure are modeled as extended Thevenin equivalents, which consist of constant resistances and time-dependent voltage sources. This new general circuit representation is compatible with existing simulation programs such as SPICE. Simulations on circuits with linear and nonlinear loads illustrate the approach. >

Transient simulation of arbitrary nonuniform interconnection structures characterized by scattering parameters

Abstract: A noniterative time-dependent circuit model is presented for transient analysis of general uniform and nonuniform interconnection structures terminated with arbitrary, linear or nonlinear loads. Simulated or measured scattering parameter data are used to characterize the interconnection structures. No approximations or model fitting are required. At each point in time, all coupled ports of the interconnection structure are modeled as extended Thevenin equivalents, which consist of constant resistances and time-dependent voltage sources. This new general circuit representation is compatible with existing simulation programs such as SPICE. Simulations on circuits with linear and nonlinear loads illustrate the approach. >

Loss modeling of converter induction machine system for variable speed drive

Abstract: The authors describe a unified loss model of a converter induction machine system such that steady state loss characteristics as well as the dynamic behavior of both machine and converter are accurately represented. The machine electrical losses. such as stator and rotor copper loss, core loss, and stray loss, are considered for both fundamental and harmonic frequencies. Also considered are the skin effect on rotor resistance, the temperature effect on both stator and rotor resistances, magnetizing inductance saturation, and friction and windage loss. All these features are incorporated in synchronously rotating frame dynamic D/sup e/-Q/sup e/ equivalent circuits. A converter system that includes a diode rectifier and pulse-width modulation transistor inverter has been modeled accurately for conduction and switching losses. The machine and converter drive system, and been simulated for a vector-controlled drive system, and validity in both steady state and transient condition has been verified. >

Transient semiconductor device simulation including energy balance equation

Abstract: An efficient numerical method for the solution of hot‐carrier transport equations describing transient processes in submicrometer semiconductor devices is proposed. The calculations of transient processes in submicrometer MOS transistor were carried out and compared with the results obtained by conventional drift‐diffusion model.

Transient simulation of nonuniform coupled lossy transmission lines characterized with frequency-dependent parameters. I. Waveform relaxation analysis

Abstract: Presents a waveform relaxation technique for simulating the transient response of nonuniform coupled transmission lines which are characterized with frequency-dependent parameters. The method consists of iterative waveform relaxation analysis of asymmetric disjoint resistive networks constructed with voltage-dependent voltage sources generated by applying the fast Fourier transform (FFT). The method requires neither convolution integration nor synthesis of lumped equivalent circuits for the simulation of the frequency-dependence of transmission-line parameters. Transient responses of uniform and nonuniform coupled transmission lines with and without skin-effect parameters and terminated with linear and nonlinear loads are simulated for illustration. The accuracy and efficiency of the relaxation technique are substantiated with exact analytical solutions and experimental data. >

Gas-dependent response in the temperature transient of SnO2 gas sensors☆

Abstract: This paper describes the gas-dependent response observed in the transient conductance patterns caused by surface temperature changes in various types of SnO2 gas sensors. These sensors have been investigated for the purpose of gas identification. The underlying objective of this research is how to extract gas-specific information to the fullest extent from a single gas sensor. In this case a temperature transient method is used. A step-like change in its heater voltage causes a conductance change in the sensor, resulting in a gas-dependent transient response. We examine the transient responses after dividing them by the conductance response when measured in clean air, and distinctive peaks are observed. The peak times depend on the particular gas species. Therefore this method will be useful for identifying gas species. The characteristics of several types of gas sensor have also been studied. We observe that the same types of sensor show similar gas dependency characteristics. Other types of sensor show different peak delay times. However, they all have gas-dependent features in common.

Generalized moment-matching methods for transient analysis of interconnect networks

Abstract: An approach is introduced which improves published moment matching methods used in transient waveform estimation of large linear networks including lossy, coupled transmission lines. The method, which selects from a general set of moment-matching approximations, ensures stability while increasing the accuracy of the transient response. The technique is useful for analysis of high-speed interconnects including lumped and distributed linear components with nonlinear terminations. Examples are presented which demonstrate the stability and accuracy of the new method. >

Application of robust control to sustained oscillations in power systems

Abstract: Transient control of the sustained oscillations that can occur after a major disturbance to a power system is investigated. A control scheme for an n-generator system is first developed using a classical machine model, and then extended to a machine model that includes governor/turbine dynamics. The proposed control strategies are linear and require only local relative angle and velocity measurements for the classical model case, plus the measurement of mechanical power if governor/turbine dynamics are included. Using Lyapunov's direct method, the control is shown to be robust with respect to parameter and load variations, and topology changes in the power system. The overall power system is shown to be exponentially stable in the main so that any oscillation, anywhere in the system, can be damped efficiently. The results are obtained without any linearization of the power system model. Simulation results for the 30-bus New England system demonstrate the effectiveness of the proposed control. >

Measurement of steady-state and transient load-angle, angular velocity, and acceleration using an optical encoder

Abstract: The measurement of steady-state and transient load-angle, angular velocity, and acceleration using an optical encoder is described. The accuracy of measurement is assessed, and results are given for the run-up of a three-phase reluctance motor. Accurate values of speed and load-angle are determined, but the measurement of acceleration is more difficult, and significant errors are present for values in excess of approximately 50 mechanical rad/s/sup 2/. Predicted results for a computer model are in reasonable agreement. >

A precise model for the transient characteristics of power diodes

Abstract: A power diode model for circuit simulations is described. All important phenomena like transient behavior, temperature dependence, emitter recombination, mobile charge carriers in depletion layer, carrier multiplication, and self-heating are included. Comparisons between simulations and measurements show less than 10% deviation of current and voltage over the temperature range of 25 degrees C-125 degrees C. >

Transient grating effects in absorbing colloidal suspensions

Abstract: The time dependence of the refractive index change induced in an absorbing colloidal suspension by a nanosecond laser pulse is studied by the four‐wave mixing method. A very large transient is observed even in very dilute suspensions whose amplitude oscillates on a time scale much shorter than the laser pulse duration; the effect is found in a variety of systems. The behavior of the transient suggests that it is associated with an acoustic wave in the suspending fluid excited by an explosive event at the surface of the particles. By comparing the predictions of various hydrodynamic models with the observations and by studying the effect of changing the experimental conditions on the form of the transient, it is proposed that the behavior arises from the very rapid growth of vapor bubbles around those particles which are heated sufficiently strongly; the four‐wave mixing signal monitors the coherent superposition of the resulting pressure pulses in the fluid.

Transient analysis of nonuniform transmission lines

Abstract: The transient propagation through nonuniform transmission line structures is analyzed. Nonuniform structures include tapered microstrips and uniform lines with periodic and nonperiodic loadings or discontinuities. The analysis employs a scattering parameter formulation in the time domain to derive closed-form algorithms for the voltage and current variables in the line. The solutions that can be used in the case in which both discontinuities and terminations are nonlinear avoid the use of transforms or convolutions and thus are computationally efficient. Simulation algorithms are tested and, when compared with experimental simulations, indicate good agreement. >

Notes on Transient THD Effects in a Lubricating Film

Abstract: An analysis of the transient thermohydrodynamic behavior of the lubricating film in a journal bearing is presented. The energy equation and the Reynolds equation are uncoupled and a simplified form of the energy equation is derived by integrating an assumed form of temperature distribution across the film thickness. This equation gives the mean film temperature subjected to an adiabatic boundary condition at the oil-bush interface and a boundary condition that imposes a uniform circumferential temperature at the oil-shaft interface. An algorithm is developed which efficiently solves the equation for the transient, mean film temperature. Numerical results are presented for several operating parameters.

Analytic transient solution of general MOS circuit primitives

Abstract: The exact analytic transient solution is presented for a general MOS circuit primitive. In the circuit primitive, I-V characteristics of transistors are modeled by quadratic equations and node voltages by piecewise-linear waveforms. The proposed MOS circuit primitive, of which an inverter is a special case, is shown to be more suitable for switch level and fast timing simulations than the commonly used inverter. For circuit simulation of medium-size digital circuits containing a few hundred transistors, the application of this analytic solution has resulted in two to three orders of speed improvement over the conventional circuit simulator. The speed improvement factor is expected to grow with the circuit size. It is also shown that the exact transient solution of a macromodel which models the charge sharing can be obtained in the same way. >