Showing papers on "Transient (oscillation) published in 2003"

Trends and challenges in VLSI circuit reliability

Abstract: Deep-submicron technology is having a significant impact on permanent, intermittent, and transient classes of faults. This article discusses the main trends and challenges in circuit reliability, and explains evolving techniques for dealing with them.

A comparative analysis of multiloop voltage regulation strategies for single and three-phase UPS systems

Abstract: Most of the many reported control algorithms for uninterruptible power supplies (UPSs) use either filter inductor or filter capacitor currents as feedback variables to regulate the output voltage. This paper explores the fundamental performance issues associated with the use of these quantities as feedback variables, with a view to determining their contribution to the transient system response and output harmonic compensation in any particular situation. A proportional plus resonant (P+resonant) compensator is then added into the outer voltage regulation loop to achieve zero steady error, to develop a high performance UPS control algorithm, which is applicable to both single-phase and three-phase systems. Theory, simulation, and experimental results are presented in the paper.

Representing wind turbine electrical generating systems in fundamental frequency simulations

Abstract: Increasing numbers of wind turbines are being erected. In the near future, they may start to influence the dynamics of electrical power systems by interacting with conventional generation equipment and with loads. The impact of wind turbines on the dynamics of electrical power systems therefore becomes an important subject, studied by means of power system dynamics simulations. Various types of power system dynamics simulations exist and the approach depends on the aspect of power system dynamic behavior being investigated. In this paper, the focus is on fundamental frequency simulations, also known as electromechanical transient simulations. In this type of simulation, the network is represented as an impedance matrix and only the fundamental frequency component of voltages and currents is taken into account in order to reduce the computation time. This simulation approach is mainly used for voltage and angle stability investigations. Models of wind turbine generating systems that match the fundamental frequency simulation approach are presented and their responses are compared to measurements.

A solution of optimal power flow with multicontingency transient stability constraints

Abstract: This paper presents a formulation of the multicontingency transient stability constrained optimal power flow (MC-TSCOPF) problem and proposes a method to solve it. In the MC-TSCOPF formulation, this paper introduces a modified formulation for integrating transient stability model into conventional OPF, which reduces the calculation load considerably. In our MC-TSCOPF solution, the primal-dual Newton interior point method (IPM) for nonlinear programming (NLP) is adopted. Computation results on the IEEJ WEST10 model system demonstrate the effectiveness of the presented MC-TSCOPF formulation and the efficiency of the proposed solution approach. Moreover, based on quite convincing simulation results, some phenomena occurred when considering multicontingency are elaborated.

A new algorithm for transient motor current signature analysis using wavelets

Abstract: A new algorithm is introduced for motor current signature analysis of induction machines operating during transients. The algorithm is able to extract the amplitude, phase and frequency of a single sinusoid embedded in a nonstationary waveform. The algorithm is applied to the detection of broken rotor bars in induction machines during startup transients. The fundamental component of current, which varies in amplitude, phase, and frequency, is extracted using the algorithm. The residual current is then analyzed using wavelets for the detection of broken rotor bars. This method of condition monitoring does not require parameters such as speed or number of rotor bars, is not load dependent and can be applied to motors that operate continuously in the transient mode, e.g., wind generators or motor-operated valves.

Circuit and method for determining battery impedance increase with aging

Abstract: An internal impedance of a battery ( 30 ) is automatically determined by operating a processor ( 13 ) to analyze current flowing through the battery to determine if a transient condition due to change of current is occurring and determining when the transient condition has ended. A voltage of the battery is measured while a steady current is being supplied by the battery. The present depth of discharge (DOD) of the battery is determined and a database is accessed to determine a corresponding value of open circuit voltage. The internal impedance is computed by dividing the difference between the measured voltage of the battery and the open circuit voltage at the present DOD by an average value of the steady current. A remaining run-time of the battery can be determined using a total zero-current capacity of the battery, integrating the current to determine a net transfer of charge from the battery, determining a value of total run-time that would be required to reduce the voltage of the battery to a predetermined lower limit, determining the duration of the integrating, and determining the remaining run-time by subtracting the duration of the integrating from the total run-time.

A hybrid inverse transient model for leakage detection and roughness calibration in pipe networks

Abstract: Leakage detection and calibration of hydraulic models are important issues for the management of water and other distribution networks. An inverse transient model based on a hybrid search technique is presented here. The inverse model is developed mainly for the detection of leaks in water distribution networks. The inverse transient procedure is formulated as a constrained optimisation problem of weighted least-squares type. Two optimisation techniques are tested: the genetic algorithm (GA) and the Levenberg-Marquardt (LM) method. After examining their performance, a new hybrid genetic algorithm (HGA) is developed to exploit the advantages of combining the two methods. The resulting HGA-based inverse transient model is compared with the GA and LM-based inverse transient models using two case studies. The HGA-based inverse transient model proved to be more stable than the LM-based model and it is more accurate and much faster than the GA-based inverse transient model.

A control strategy of single-phase active filter using a novel d-q transformation

Abstract: In this paper, a control strategy of the single-phase active filter using a novel d-q transformation is proposed This d-q transformation is implemented by using Hilbert transform, by which the instantaneous single-phase voltage and current are converted into complex vectors (analytic signals) on the instantaneous basis Since the fundamental components of voltages and currents are converted into DC components on the d-q coordinate both in the steady and transient states, the harmonics of voltages and currents can be obtained precisely through the low-pass filer installed on the d-q coordinate This results in the economical active filter with a small capacitor suppressing the DC bus voltage fluctuation because the fundamental power can be fully removed from the active filter input

Dynamic harmonic evolution using the extended harmonic domain

Abstract: A novel methodology is presented in this paper for conducting transient and steady-state analysis of electric networks containing nonlinearities and switching plants components. The method is termed the extended harmonic domain (EHD) method as may be seen as an extension of the harmonic domain (HD) method used in steady-state analysis. It is shown in the paper that EHD is a natural approach for conducting dynamic and steady-state studies of the evolution of harmonics in power circuits containing nonlinear components and flexible AC transmission systems (FACTS) devices. It is also shown in the paper that EHD provides a suitable basis for extending the well-known steady-state power quality indices to the transient range. To illustrate the use of the theory, a three-phase linear circuit and a three-phase PWM-STATCOM are modeled using EHD. The results are compared against those provided by industry standard tools as PSCAD/EMTDC and Matlab.

Numerical modeling of electrostatic discharge generators

Abstract: The discharge current and the transient fields of an electrostatic discharge (ESD) generator in the contact mode are numerically simulated using the finite-difference time-domain method. At first the static field is established. Then the conductivity of the relay contact is changed, which initiates the discharge process. The simulated data are used to study the effect of design choices on the current and fields. They are compared to measured field and current data using a multidecade broadband field and current sensors. The model allows accurate prediction of the fields and currents of ESD generators, thus it can be used to evaluate different design choices.

Design consideration of the active-clamp forward converter with current mode control during large-signal transient

Abstract: The design issues of the active-clamp forward converter circuit with peak current mode control in small signal stability and large-signal transients are discussed. A design procedure is provided to solve circuit issues under these conditions. It is the first time that with the aid of simulation, we are able to optimize the circuit design of the active-clamp forward converter for large-signal transient behaviors.

Transient response analysis for temperature-modulated chemoresistors

Abstract: This article presents a sensor excitation and signal processing approach that combines temperature modulation and transient analysis to enhance the selectivity and sensitivity of metal-oxide gas sensors. A staircase waveform is applied to the sensor heater to extract transient information from multiple operating temperatures. Four different transient analysis techniques, Pade–Z-transform, multi-exponential transient spectroscopy (METS), window time slicing (WTS) and a novel ridge regression solution, are evaluated on the basis of their ability to improve the sensitivity and selectivity of the sensor array. The techniques are validated on two experimental databases containing serial dilutions and mixtures of organic solvents. Our results indicate that processing of the thermal transients significantly improves the sensitivity of metal-oxide chemoresistors when compared to the quasi-stationary temperature-modulated responses. # 2003 Elsevier Science B.V. All rights reserved.

Analysis and control of transient dynamics of EDFA pumped by 1480- and 980-nm lasers

Abstract: The transient responses of Er-doped fiber amplifier (EDFA) to fast channel adding/dropping processes have been studied and analyzed. The result shows that the speed in which we can control EDFA with a feedback circuit is limited by the physical processes involved in the amplification. We demonstrated that with the combination of electrical feedforward and feedback, the power excursion caused by fast channel adding/dropping processes can be minimized.

One-dimensional transient radiation heat transfer modeling using a finite-volume method

Abstract: This article presents a finite-volume method to calculate transient radiative transfer in a one-dimensional slab. The fully implicit scheme is used to discretize the transient term. The step and CLAM spatial differencing schemes are used in this study. The procedure is validated with available published results. The capabilities of the procedure are then examined using three additional test problems. In these test problems, one of the walls is subjected to a single-pulse collimated beam and a repeated-pulse collimated beam. The effects of the two spatial differencing schemes are discussed.

Fault location in distribution systems based on traveling waves

Abstract: A single end fault location method for distribution systems, based on the traveling waves theory, is presented. The proposed scheme operates on the incident transient currents traveling from the fault point and measured at the substation. A cross-correlation function is used to identify the transient traveling waves. The voltages are estimates by using the transmission line modeling method while the distance to the fault is computed using the cross-correlation function. Although the complexity introduced by the many discontinuities created by the subfeeders in the system is considered, the results of several simulations and a field trial on a 23.8 kV system demonstrate the viability of this technique for distribution systems.

Transient performance study of a brushless doubly fed twin stator induction generator

Abstract: This paper presents theoretical, simulation, and experimental study of the brushless doubly fed twin stator induction generator (BDFTSIG) dynamics under vector control based on the orientation on the power machine stator flux. A complex transfer function is derived which links the control current and power winding current space vectors in the field coordinates. Based on this result, the transient response of the BDFTSIG to step changes in the control current is examined theoretically. The oscillatory transients are explained in detail and linked to control flux transients triggered whenever operation point of the generator is changed. Furthermore, BDFTSIG operation with closed loop control of the power machine active and reactive powers is examined theoretically and experimentally. It is shown that in the closed loop operation, the system damping may be reduced so that the PI controller gains must be properly selected to achieve a good transient response.

Two-Color Pump−Probe Spectroscopies of Two- and Three-Level Systems: 2-Dimensional Line Shapes and Solvation Dynamics

Abstract: For both two- and three-level systems, theoretical descriptions of two-color transient grating, transient dichroism, and transient birefringence spectroscopies were presented. The two-dimensional line shapes of these pump−probe spectra were found to be strongly dependent on the solvation dynamics. The two-dimensional contours of the transient birefringence signal of a two-level system are not vertically directed in the short time region. The inverse slope of the tangential line of the two-dimensional contours was found to be linearly proportional to the solvation correlation function. The two-dimensional transient grating and dichroism spectra are shown to directly provide quantitative information on the reorganization energy and spectral diffusion dynamics. For a three-level system that is a model for an anharmonic oscillator, the peak separation observed in a two-dimensional transient dichroism spectrum was found to be determined by both fluctuation amplitude of the transition frequency and spectral ban...

Dynamic modeling and analysis of a bimodal ultrasonic motor

Abstract: A dynamic model that includes four subsystems is developed to analyze the fundamental characteristics of a bimodal ultrasonic motor. The first subsystem is the driving circuit designed for the motor to achieve bidirectional motion. The stator is modeled as a Timoshenko beam, and the assumed mode energy method is used to obtain the dynamic equations. The normal interface force is represented by an elastic spring existing in between the tip of the stator and the moving platform. The interface forces are coupled into the dynamic formulations of the stator and the moving platform. The behavior of the force transmission between the stator and the moving platform are analyzed using the developed model. Transient and steady-state responses of the system are obtained by numerical simulation, and the results are validated by experiments. Furthermore, the existing of a nonlinear deadzone is predicted analytically, and the causes of this nonlinearity are clarified.

A diagnostic method for on-line fault detection and localization in vsi-fed ac drives

Abstract: This paper describes a novel approach to the detection and localization of semiconductor faults in VSI-fed AC drives. We use the DC-to-fundamental motor current ratio as the diagnostic variable. The method has proved to reliably detect true faults, while not issuing false alarms under transient conditions. The method has been validated by both simulation and experiment.

Transient and steady-state amplitudes of forced waves in rectangular basins

Abstract: A weakly-nonlinear analysis of the transient evolution of two-dimensional, standing waves in a rectangular basin is presented. The waves are resonated by periodic oscillation along an axis aligned with the wavenumber vector. The amplitude of oscillation is assumed to be small with respect to the basin dimensions. The effects of detuning, viscous damping, and cubic nonlinearity are all simultaneously considered. Moreover, the analysis is formulated in water of general depth. Multiple-scales analysis is used in order to derive an evolution equation for the complex amplitude of the resonated wave. From this equation, the maximum transient and steady-state amplitudes of the wave are determined. It is shown that steady-state analysis will underestimate the maximum response of a basin set into motion from rest. Amplitude response diagrams demonstrate good agreement with previous experimental investigations. The analysis is invalid in the vicinity of the “critical depth” and in the shallow-water limit. A separate analysis, which incorporates weak dispersion, is presented in order to provide satisfactory results in shallow water.

Simulation and verification of transient events in large wind power installations

Abstract: Models for wind power installations excited by transient events have been developed and verified. A number of cases have been investigated, including comparisons of simulations of a three-phase short circuit, validation with measurements of tripping of single wind turbine, islanding of a group of two wind turbines, and voltage steps caused by tripping of wind turbines and by manual transformer tap-changing. A Benchmark model is also presented, enabling the reader to test own simulation results against results obtained with models developed in EMTDC and DIgSILENT. ISBN 87-550-3030-0 ISBN 87-550-3031-9 (Internet) ISSN 0106-2840 Print: Pitney Bowes Management Services Danmark A/S, 2003

Transient optical studies of interfacial energetic disorder at nanostructured dye-sensitised inorganic/organic semiconductor heterojunctions.

Abstract: Broadening needs energy: Hole-transfer reactions at a dye-sensitised nanocrystalline TiO2/organic hole-conductor (HTM) interface are mainly driven by the free energy difference ΔG(dye-HTM). Inhomogeneous broadening of ΔG(dye-HTM) controls the yield of this interfacial charge-transfer reaction (see picture, curve b) and is therefore an important limitation on the voltage output of photovoltaic devices based upon such interfaces.