Showing papers on "Transient (oscillation) published in 1999"

Power System Dynamics: Stability and Control

Abstract: INTRODUCTION: Basic Concepts Review of Classical Methods of Analysis SYSTEM MODELLING AND DYNAMICS OF SYNCHRONOUS GENERATOR: Modelling of Synchronous Machine Excitation and Prime Mover Controllers Transmission Lines, Static VAR Compensators and Loads Dynamics of Synchronous Generator Connected to Infinite Bus SMALL SIGNAL STABILITY ANALYSIS (Low Frequency Oscillations): Analysis of Single Machine System Power System Stabilizer Analysis of Mulitmachine System SMALL SIGNAL STABILITY ANALYSIS (Subsynchronous Frequency Oscillations): Analysis of Subsynchronous Resonance Countermeasure to SSR TRANSIENT STABILITY ANALYSIS: Simulation for Study of Transient Stability Application of Energy Function Methods Transient Stability Controllers Appendix A: Introduction to Voltage Stability Appendix B: Numerical Integration Appendix C: Data of 10 Generator System Appendix D: List of Problems.

Diagnosis of continuous valued systems in transient operating regions

Abstract: The complexity of present day embedded systems (continuous processes controlled by digital processors), and the increased demands on their reliability motivate the need for monitoring and fault isolation capabilities in the embedded processors. This paper develops monitoring, prediction, and fault isolation methods for abrupt faults in complex dynamic systems. The transient behavior in response to these faults is analyzed in a qualitative framework using parsimonious topological system models. Predicted transient effects of hypothesized faults are captured in the form of signatures that specify future faulty behavior as higher order time-derivatives. The dynamic effects of faults are analyzed by a progressive monitoring scheme till transient analysis mechanisms have to be suspended in favor of steady state analysis. This methodology has been successfully applied to monitoring of the secondary sodium cooling loop of a fast breeder reactor.

A simplified model for zinc oxide surge arresters

Abstract: A model for metal-oxide surge arresters, derived from that one recommended from the IEEE W.G. 3.4.11, is presented. The main innovation introduced by the paper lies in the simplicity of the criteria proposed for the model's parameter identification. Such criteria allow calculation of the model parameters directly from the standard data reported in the arrester data-sheets with a simple and straightforward procedure. The effectiveness of the model was tested for several arresters of different manufacturer both for medium voltage and for high voltage application. The discharge test results obtained by the manufacturers were compared with the results of simulations performed with the Alternative Transient Program (ATP). Effectiveness and simplicity of use make the proposed model a useful tool for insulation coordination studies involving steep front transients.

Transient modeling and simulation of a tubular solid oxide fuel cell

Abstract: This paper describes the development of a computer model for simulating the transient operation of a tubular solid oxide fuel cell (SOFC). The model includes the electrochemical, thermal, and mass flow elements that affect SOFC electrical output. The electrochemical and thermal parts of the model were developed and verified separately before they were combined to form the transient model. The results of model verification tests are presented. Transient simulations were conducted with constant reactant flows and constant inlet temperatures. The transient electrical response of the cell to a load change is described.

Performance comparison of three identification methods for the analysis of electromechanical oscillations

Abstract: This paper describes the results of a study to evaluate the performance of three identification methods for the study of low frequency electromechanical oscillations. The three identification methods considered are: the Steiglitz-McBride algorithm; the eigensystem realization algorithm; and the Prony method. The identification methods are used to identify low order linear systems of power systems modeled in standard transient stability programs. This is accomplished by processing the system response to a simple probing pulse. The frequency domain characteristics of several identified systems are compared using three power systems with lightly damped electromechanical modes.

Apparatus and method for chronic measurement of monophasic action potentials

Abstract: Apparatus and methods adapted for in vivo chronic measurement of cardiac monophasic action potentials (MAPs). The methods include, inter alia, providing a sensing electrode in contact with cardiac tissue and a reference electrode in proximity to the sensing electrode, intermittently inducing a transient localized depolarization or transient injury-like electrical currents in at least some of the cells of the cardiac tissue underlying or adjacent to the sensing electrode and measuring the potential difference between the sensing electrode and the reference electrode during at least part of the duration of the depolarization or injury-like currents. Other methods for inducing depolarization or injury-like currents in the tissue include, inter alia, localized membrane electroporation, localized electrostatic production of depolarization using voltage clamp to produce a signal representative of MAPs, localized tissue heating, localized application of ultrasound and localized irradiation with light. The apparatus and methods may also be applied for non-chronic measurement of cardiac monophasic action potentials and for measurement of monophasic action potentials from other non-cardiac excitable tissues.

Sensitivity of Transient Evoked and Distortion Product Otoacoustic Emissions to the Direct Effects of Noise on the Human Cochlea

Abstract: Measurement of otoacoustic emissions (OAEs) has been proposed as a sensitive test t reliably assess the effects of noise exposure. The present study in humans was designed t evaluate the sensitivity and applicability of transient evoked OAEs (TEOAEs) and 2fl-f distortion product OAEs (DPOAEs) as quantitative indices of the functional integrity of th outer hair cells (OHC) during growth of and recovery from temporary threshold shift (TTS This was examined in two different groups of volunteers by measuring the per- and pos stimulatory effects of a one hour BBN and an on-site five hour exposure to loud music froi a discotheque. The results of both experiments show consistent growth and recover patterns for both DPOAEs and TEOAEs. For TEOAEs, both the reproducibility scores an signal to noise ratio values for the 4 kHz frequency band exhibited the greatest sensitivit The DPOAEs, on the other hand, showed the greatest sensitivity between 2 and 5.5 kH. Thus, both the TEOAEs and DPOAEs have a great potential in ...

Process control by transient thermography

Abstract: A method and apparatus for detecting, locating, isolating and controlling variations in the manufacturing process by transient thermography. A heat source (200) imparts heat to a surface which is radiated in the infrared region. Infrared sensors (204, 206, 208, 210) are coupled to a processor which tracks the physical characteristics of the sample, and provides feedback to a central process controller to make adjustments to the manufacturing process. The sample can be a continuous product such as a green powder metal sheet or tobacco product.

Controlling transient chaos in deterministic flows with applications to electrical power systems and ecology

Abstract: Transient chaos is a common phenomenon in nonlinear dynamics of many physical, biological, and engineering systems. In applications it is often desirable to maintain sustained chaos even in parameter regimes of transient chaos. We address how to sustain transient chaos in deterministic flows. We utilize a simple and practical method, based on extracting the fundamental dynamics from time series, to maintain chaos. The method can result in control of trajectories from almost all initial conditions in the original basin of the chaotic attractor from which transient chaos is created. We apply our method to three problems: (1) voltage collapse in electrical power systems, (2) species preservation in ecology, and (3) elimination of undesirable bursting behavior in a chemical reaction system.

Shared-bus current sharing parallel connected current-mode DC to DC converters

Abstract: A power system consisting of parallel connected current-mode power converters combined with a voltage error signal on a shared-bus used in common for controlling all of the power stages for improved consistency, reliability, and performance in both transient and steady states. Near uniform current sharing is achievable without sacrificing the voltage regulation performance. The improved system offers faster settling time under step loads, consistent small signal characteristics and large signal responses regardless of mismatches of components values such as reference voltages, and reduced output impedance variations in magnitude and phase even during various modes of operation.

Efficient inverse transient analysis in series pipe systems

Abstract: Measurement of the changes in heads initiated by a valve closure are used to calibrate the friction factors in a hydraulic system consisting of a series-connected pipeline and a downstream valve joining two reservoirs. The calibration is performed by minimizing the inverse least-squares problem representing the difference between the measured and predicted transient response in the network. The hydraulic transient is modeled using the method of characteristics. Unlike previous approaches, the sensitivity information required for the minimization or error is obtained by direct differentiation of the method of characteristic equations and the valve equation with respect to the friction factors. The sensitivity of the calibration results to the amount of data included in the analysis, the initial friction factor estimates, and modeling and simulated measurement errors is discussed.

Stability and control of HVDC and AC transmissions in parallel

Abstract: A generic concept combining transient angle and voltage stabilities of parallel AC/DC transmission is introduced. It proves that HVDC schemes in parallel operation with AC transmission are prone to both transient swing angle and voltage instabilities. This tendency is intensified as the parallel AC interconnection becomes stronger. The concept also explains why an HVDC scheme fitted with classical DC power controls does not contribute to system synchronizing torque and may increase the risks for instability. The concept offers a solid means to develop robust strategies to control the dynamic operation of DC and AC transmissions in parallel. With such strategies, the HVDC scheme can positively participate in the instantaneous rescheduling of power according to arising network conditions, particularly during disturbance conditions.

Three-dimensional odor compass

Abstract: A three-dimensional odor compass is proposed to develop a navigation tool used in searching for an odor source. The compass, which continuously points to the source, is equipped with four semiconductor gas sensors and a small fan to draw air to the sensors. The direction of the source is obtained by rotating the compass head to obtain the direction where the responses of the sensors along the horizontal and vertical directions are balanced. The following algorithmic improvements have been made to reduce the measurement time after the previous report on the two-dimensional compass. First, the transient sensor response model is introduced to compensate the response delay of the gas sensors. Secondly, the head of the compass is made to rotate continuously and three-dimensionally during the directional estimation to gather plenty of data over a short time period. As a result, the measurement time at a practical level (20 s) has been achieved. The experimental results demonstrate the effectiveness of the compass in practical environments where the wind blows three-dimensionally and/or where the odor distribution is modified by an obstacle.

Transient stability-constrained optimal power flow

Abstract: This paper proposes a new approach able to maximize the interface flow limits in power systems and to find a new operating state that is secure with respect to both, dynamic (transient stability) and static security constraints. It combines the maximum allowable transfer (MAT) method, recently developed for the simultaneous control of a set of contingencies, and an optimal power flow (OPF) method for maximizing the interface power flow. The approach and its performances are illustrated by means of simulations carried out on a real world power system.

Transient stability-constrained maximum allowable transfer

Abstract: A method is proposed for allocating generation so as to maximize power transfer between areas of interconnected power systems under transient stability constraints. This "transient stability-constrained maximum allowable transfer" (MAT) method consists of screening a large number of contingencies, scrutinizing the dangerous ones and suggesting generation rescheduling patterns to stabilize them. The MAT method is based on SIME, a hybrid transient stability method. Like SIME, MAT is accurate and free from simplifying assumptions about modelling, stability scenarios and instability modes. In addition, by controlling all dangerous contingencies simultaneously, the method succeeds in being fully compatible with requirements for real-time preventive monitoring and control. The method is illustrated on the South-Southeast Brazilian power system, operating under highly stressed conditions imposed by large power transfer between areas.

Transient performance of an isolated induction generator under unbalanced excitation capacitors

Abstract: This paper presents transient performance of a stand-alone self-excited induction generator (SEIG) under unbalanced excitation capacitors. An approach based on a three-phase induction machine model is employed to derive dynamic equations of an isolated SEIG under unbalanced conditions. The neutral points of both a Y-connected excitation capacitor bank and Y-connected stator windings of the SEIG is connected together through a neutral line. Experimental results obtained from a laboratory 1.1 kW induction machine driven by a DC motor are also performed to confirm the feasibility and effectiveness of the proposed method.

Modeling of power distribution systems for high-performance microprocessors

Abstract: This paper presents approximate techniques for building models and simulating the response of power distribution systems for high-performance microprocessors. Several distributed equivalent SPICE circuit models were built by extracting the appropriate resistance, inductance, capacitance (RLC) component values using a combination of two-dimensional (2-D) and three-dimensional (3-D) quasi-static field solvers. They were used to assess how well such effects as system transfer impedance and transient characteristics can be predicted. The models include the chip, its controlled collapsed chip connection (C4) connections to the package, the power distribution structure in the package, connector and motherboard. It is found that the response of the entire power system can be treated as a second order system, by which the main features of the performance of the power delivery network are assessed. Samples of transient and frequency domain data for typical microprocessors are given and the effects of some design options are discussed, as are the tradeoffs in model complexity versus the gain of useful design information.

Approaches for analog VLSI simulation of the transient stability of large power networks

Abstract: This paper suggests several approaches for determining the transient stability of a power network by using an analog VLSI chip for simulating the system behavior. The main advantages of using this method are the much shorter computation time and lower complexity compared to the currently used methods, which are based on numerical calculations or discrete analog emulators.

Modelling of windmill induction generators in dynamic simulation programs

Abstract: For AC networks with large amounts of induction generators-in case of eg windmills-the paper demonstrates a significant discrepancy in the simulated voltage recovery after faults in weak networks, when comparing result obtained with dynamic stability programs and transient programs, respectively with and without a model of the mechanical shaft The reason for the discrepancies are explained, and it is shown that the phenomenon is due partly to the presence of DC offset currents in the induction machine stator, and partly to the mechanical shaft system of the wind turbine and the generator rotor It is shown that it is possible to include a transient model in dynamic stability programs and thus obtain correct results also in dynamic stability programs A mechanical model of the shaft system has also been included in the generator model

Low capacitance surge protector for high speed data transmission

Abstract: The present invention is a surge protector circuit and method of protecting electronic equipment which do not load down a circuit at high frequencies and do not degrade a signal in high speed data transmission. A gas tube is connected in parallel with low capacitance diodes and an avalanche semiconductor device, such as a TVS. The diodes and the avalanche semiconductor clamp the voltage transient and allow the slower gas tube more time to fire, discharging the surge. The addition of the low capacitance diodes in series with the avalanche semiconductor, reduces the line-to-line and line-to-ground capacitances of the surge protector and keeps the surge protector circuit from loading down the rest of the circuit and degrading the signal.

A power conditioner for a grid-connected photovoltaic generator based on the 3-level inverter

Abstract: This paper describes the fundamental design of a novel power conditioner for medium size photovoltaic generators. The proposed conditioner employs several poles of the 3-level inverter, which, configured through current sharing reactors, can provide a multi-level voltage. The conditioner provides maximum power point tracking and power factor correction by direct control of the instantaneous value of the inverter output current. A PWM-gate control is derived which utilizes the multilevel form of the output voltage and effectively increases the switching frequency of the inverter without increasing the switching frequency of its valves. Simulation studies in the paper verify the steady state and transient performance of the proposed conditioner. The simulation results show that implementation of the proposed design could significantly improve the power quality of photovoltaic generators.

Distribution system compensation using a new binary multilevel voltage source inverter

Abstract: A new binary multilevel voltage source inverter with separate DC sources is proposed. This n-level voltage source inverter produces a (2/sup n+1/-1)-steps AC voltage output with n full bridge inverters connected in series. The use of selective harmonic elimination modulation technique to either completely eliminate or minimize harmonics is studied. A closed-loop controller to control the capacitor voltages and adjust the inverter reactive power output is developed. Application of such a compensator for dynamic compensation of 13.8 kV distribution system is examined through transient studies using a PSCAD/EMTDC program. The proposed inverter configuration not only reduces the system complexity and its size, but also improves the harmonic profile significantly.

Transient modeling and simulation of a SMES coil and the power electronics interface

Abstract: This paper presents the modeling and simulation results of a superconducting magnetic energy storage (SMES) system for power transmission applications. This is the largest SMES coil ever built for power utility applications and has the following unique design characteristics: 50 MW (96 MW peak), 100 MJ, 24 kV dc interface. As a consequence of the high-power and high-voltage interface, special care needs to be taken with overvoltages that can stress the insulation of the SMES coil, especially in its cryogenic operating environment. The transient overvoltages impressed on the SMES coil are the focus of this investigation. Suppression methods were also studied to minimize transients. The simulation is based on detailed coil and multiphase gate turn-off (GTO)-based chopper models. The study was performed to assist in the design of the SMES coil insulation, transient protection, and the power electronics specification and interface requirements.

Dynamic Behaviour of a High Speed Direct Injection Diesel Engine

Abstract: Many Diesel engine development programs concentrate almost exclusively on steady state investigations to benchmark an engines performance. In reality, the inter-action of an engine's sub-systems under transient evaluation is very different from that evident during steady state evaluation. The transient operation of a complete engine system is complex, and collecting test data is very demanding, requiring sophisticated facilities for both control and measurement. This paper highlights the essential characteristics of a Diesel engine when undertaking testbed transient manouevres. Results from simple transient sequences typical of on-road operation are presented. The tests demonstrate how transient behaviour of the engine deviates greatly from the steady state optimum settings used to control the engine. The operation of the EGR system and its interaction with other sub-systems, in particular VGT, has a significant effect on emissions, fuel consumption and driveability, highlighting the need for dynamic optimisation as an integrated system.

Two flux weakening schemes for surface-mounted permanent-magnet synchronous drives. Design and transient response considerations

Abstract: Two recently published flux weakening schemes for surface-mounted permanent-magnet synchronous (SMPMS) motor drives have offered estimable advantages over previous solutions. The first scheme uses values of the voltage reference to generate an adequate flux weakening component of the stator current, whereas the second method detects an increase of the tracking error in torque-producing current component and uses the error signal for the flux weakening control. The viability of the algorithms has been demonstrated and the schemes have been compared and analyzed in steady-state operation. The transient behavior is very important for electric vehicles and other high-performance applications. Here, the authors analyze the transient response characteristics of both schemes when a sudden change in the torque reference is received. The paper also describes an approach to practical regulator design and parameter selection for the flux weakening control section.

Quantitative feedback theory control of a single-link flexible manipulator featuring piezoelectric actuator and sensor

Abstract: This paper presents robust control of a single-link flexible manipulator which consists of two actuators: a motor mounted at the hub and a piezoceramic bonded to the surface of the flexible link The control torque of the motor activates desirable hub motion and the control voltage of the piezoceramic actively suppresses undesirable vibration of the flexible link yielding an accurate endpoint position of the manipulator As a first step to achieve this control target, two transfer functions are established in the Laplace domain; one is from input torque to output hub angle and the other is from input voltage to output tip-deflection The QFT (quantitative feedback theory) is then adopted to formulate robust controllers associated with two actuators Two QFT compensators are designed on the basis of a stability criterion which prescribes a bound on the peak of an M-contour in the Nichols chart (NC) In the formulation of the compensator for the piezoceramic, the hysteresis behavior is considered as a structured plant uncertainty A prefilter for the motor is subsequently designed in order to improve the transient and steady state control responses Tracking control characteristics are analysed through computer simulation and experimental implementation in order to demonstrate the effectiveness of the proposed control methodology

Polymer composite materials for electrostatic discharge protection

Abstract: A composition for providing protection against electrical overstress (EOS) comprising an insulating binder, doped semiconductive particles, and semiconductive particles. The composite materials exhibit a high electrical resistance to normal operating voltage values, but in response to an EOS transient switch to a low electrical resistance and clamp the EOS transient voltage to a low level for the duration of the EOS transient.

Influence of aging on electrolytic capacitors function in static converters: Fault prediction method

Abstract: The failure of electrolytic capacitors is the cause of most breakdowns of static converters The function of these capacitors is to filter and to store electrical energy Accelerated aging tests showed that the increase of the internal resistance ESR of the capacitors is a good indicator of their faulty state The filter function is affected by the capacitors wearout on the one hand At high frequency, the voltage ripple at the terminals of the capacitors increases according to ESR rise On the other hand, the storage function is not much influenced by the capacitors aging As static converters work most of the time at variable load, high transient values of the voltage ripple occur when output current changes that can induce false alarms These transients are verified theoretically and experimentally In order to avoid these transients effects, we suggest to monitor the fundamental component of the voltage ripple This latter waveform is the best signature of the capacitors state The ESR of the capacitors and the time before their failure are deduced from the processing of this waveform with other converter parameters such as input voltage, output current and ambient temperature

Robust adaptive control of robots with arbitrary transient performance and disturbance attenuation

Abstract: We consider the tracking problem for robot manipulators with unknown and (possibly) time-varying parameters, which are subject to bounded disturbances. We provide a state feedback adaptive control algorithm which guarantees arbitrary transient performance as well as arbitrary disturbance attenuation. If the disturbances vanish and the parameters remain constant, the proposed controller achieves asymptotic tracking.