Showing papers on "Transient (oscillation) published in 2010"

Novel STATCOM Controller for Mitigating SSR and Damping Power System Oscillations in a Series Compensated Wind Park

Abstract: This paper addresses implementation issues associated with a novel damping control algorithm for a STATCOM in a series compensated wind park for mitigating SSR and damping power system oscillations. The IEEE first benchmark model on SSR is adopted with integrating aggregated self-excited induction generator-based wind turbine to perform the studies. The potential occurrence and mitigation of the SSR caused by induction generator effects as well as torsional interactions, in a series compensated wind park, are investigated. The auxiliary subsynchronous damping control loop for the STATCOM based on a novel design procedure of nonlinear optimization is developed to meet the damping torque in the range of critical torsional frequencies. The intelligent shaft monitor (ISM) scheme with synthesized special indicator signals is developed and examined in the STATCOM control structure. The performances of the controllers are tested in steady-state operation and in response to system contingencies, taking into account the impact of SCRs. Simulation results are presented to demonstrate the capability of the controllers for mitigating the SSR, damping the power system oscillation, and enhancing the transient stability margin in response to different SCRs.

Feed-Forward Transient Current Control for Low-Voltage Ride-Through Enhancement of DFIG Wind Turbines

Abstract: High penetration of wind power requires reliable wind energy generation. A successful low-voltage ride-through (LVRT) scheme is a key requirement to achieve reliable and uninterrupted electrical power generation for wind turbines equipped with doubly fed induction generators (DFIGs). This paper proposes a feed-forward transient current control (FFTCC) scheme for the rotor side converter (RSC) of a DFIG to enhance its LVRT capability. This new control scheme introduces additional feed-forward transient compensations to a conventional current regulator. When three phase faults occur, these compensation terms correctly align the RSC ac-side output voltage with the transient-induced voltage, resulting in minimum transient rotor current and minimum occurrence of crowbar interruptions. With little additional computational effort, the proposed control scheme helps relieve the transient current stress on the RSC and helps maintain an uninterrupted active and reactive power supply from the wind turbines to the power grid. Simulation results are shown to demonstrate the effectiveness of the proposed FFTCC scheme in suppressing transient rotor currents.

Securing Transient Stability Using Time-Domain Simulations Within an Optimal Power Flow

Abstract: This paper provides a methodology to restore transient stability. It relies on a well-behaved optimal power flow model with embedded transient stability constraints. The proposed methodology can be used for both dispatching and redispatching. In addition to power flow constraints and limits, the resulting optimal power flow model includes discrete time equations describing the time evolution of all machines in the system. Transient stability constraints are formulated by reducing the initial multi-machine model to a one-machine infinite-bus equivalent. This equivalent allows imposing angle bounds that ensure transient stability. The proposed optimal power flow model is tested and analyzed using an illustrative nine-bus system, the well-known New England 39-bus system, a ten-machine system, and a real-world 1228-bus system with 292 synchronous machines.

Steady periodic memristor oscillator with transient chaotic behaviours

Abstract: By replacing Chua's diode in the canonical Chua's oscillator with a smooth flux-controlled memristor, a memristor based oscillator is presented. The memristor oscillator generates a steady periodic orbit and has a transition from transient chaotic to steady periodic behaviour. The complicated dynamical behaviour is extremely dependent on the initial condition of the memristor.

Transient Operation of a Four-Leg Inverter for Autonomous Applications With Unbalanced Load

Abstract: In this paper, the transient operation of a four-leg inverter equipped with an innovative control strategy under unbalanced load conditions is investigated The inverter is proposed for transformerless hybrid power system applications, in order to provide simultaneous supply of three-phase and single-phase AC loads with balanced voltage and constant frequency The four-leg inverter is controlled to ensure balanced voltage by means of a control strategy based on the decomposition of the supply three-phase voltage and current into instantaneous positive, negative, and homopolar sequence components using phasor representation These three sequences are controlled independently in their own reference frames as DC signals The implementation derived for the controller design is also described The transient operation performance of the proposed control strategy has been tested in simulations with an average model and experimentally using a laboratory prototype

Methods and Apparatuses for Monitoring Energy Consumption and Related Operations

Abstract: Apparatus and method including acquiring a signal indicative of power consumption; detecting a transient in the signal; extracting a feature indicative of the transient, wherein extracting the feature includes: fitting a plurality of models to the transient, selecting one of the plurality of models as a model for the transient, and defining the feature indicative of the transient based on at least one parameter of the model for the transient; and classifying the transient based on the feature.

Historical Evolution of the Transient Hot-Wire Technique

Abstract: The paper attempts to describe the historical evolution of the transient hot-wire technique, employed today for the measurement of the thermal conductivity of fluids and solids over a wide range of conditions. Starting from the first experiments with heated wires in 1780 during the discussions of whether gases could conduct heat, it guides the reader through typical designs of cells and bridges, software employed and theory developed, to the modern applications. The paper is concluded with a discussion of the areas of application where problems still exist, and a glimpse of the technique’s future.

A Real-Time Thermal Model of a Permanent-Magnet Synchronous Motor

Abstract: This paper presents a real-time thermal model with calculated parameters based on the geometry of the different components of a permanent-magnet synchronous motor. The model in state-space format has been discretized and a model-order reduction has been applied to minimize the complexity. The model has been implemented in a DSP and predicts the temperature of the different parts of the motor accurately in all operating conditions, i.e., steady-state, transient, and stall torque. The results have been compared with real measurements using temperature transducers showing very good performance of the proposed thermal model.

Quantitative evaluation of angular defects by pulsed eddy current thermography

Abstract: Pulsed eddy current (PEC) thermography employs a combination of PEC and thermographic non-destructive testing (NDT) techniques. This study considers the capabilities of PEC thermography for obtaining quantitative information about cracks set at an angle to the surface. The investigation is implemented by simulating the transient thermal distribution for angular slots, via time-stepping 3D finite element analysis (FEA), with the experimental work undertaken for verification. A slope inclination feature of the transient temperature distribution has been extracted and presented for estimating the angle of slots that is independent of slot depth and length inside the sample. With the identification of the slot angle, quantification of the length/depth of the slot inside the sample can then be made through a maximum temperature amplitude feature. Experimental studies have been undertaken for evaluation of the numerical simulation and transient feature extraction methods.

Transient energy excitation in shortcuts to adiabaticity for the time-dependent harmonic oscillator

Abstract: We study for the time-dependent harmonic oscillator the transient energy excitation in speed-up processes ('shortcuts to adiabaticity') designed to reproduce the initial populations at some predetermined final frequency and time. We provide lower bounds and examples. Implications for the limits imposed to the process times and for the principle of unattainability of the absolute zero, in a single expansion or in quantum refrigerator cycles, are drawn.

Fast infrared variability from a relativistic jet in GX 339-4

Abstract: We present the discovery of fast infrared/X-ray correlated variability in the black hole transient GX 339-4. The source was observed with subsecond time resolution simultaneously with Very Large Telescope/Infrared Spectrometer And Array Camera and Rossi X-ray Timing Explorer/Proportional Counter Array in 2008 August, during its persistent low-flux highly variable hard state. The data show a strong correlated variability, with the infrared emission lagging the X-ray emission by 100 ms. The short time delay and the nearly symmetric cross-correlation function, together with the measured brightness temperature of similar to 2.5 x 10(6) K, indicate that the bright and highly variable infrared emission most likely comes from a jet near the black hole. Under standard assumptions about jet physics, the measured time delay can provide us a lower limit of Gamma > 2 for the Lorentz factor of the jet. This suggests that jets from stellar-mass black holes are at least mildly relativistic near their launching region. We discuss implications for future applications of this technique.

Comparison of Stabilization Methods for Fixed-Speed Wind Generator Systems

Abstract: Static synchronous compensator (STATCOM), pitch control system, braking resistor (br), and superconducting magnetic energy storage (SMES) have recently been reported as stabilization methods for fixed-speed wind generator systems. Although the individual technologies are well documented, a comparative study of these systems has not been reported so far. This paper aims to fill in the gap, and provides a comprehensive analysis of these stabilization methods for fixed-speed wind generator systems. The analysis is performed in terms of transient stability enhancement, controller complexity, and cost. A novel feature of this work is that the transient stability analysis of wind generator system is carried out considering unsuccessful reclosing of circuit breakers. Simulation results demonstrate that the SMES is the most effective means of transient stability enhancement and minimization of both power and voltage fluctuations, but it is the most expensive device. The STATCOM is a cost-effective solution for transient stability enhancement and minimization of voltage fluctuations. The BR is the simplest in structure and a cost-effective solution for transient stability enhancement. The pitch controller is the cheapest one, but its response is much slower than that of other devices.

Global Transient Stability-Constrained Optimal Power Flow Using an OMIB Reference Trajectory

Abstract: This paper presents a new approach to transient stability control using global transient stability-constrained optimal power flow (TSC-OPF) methods. Its novelty consists in using the single machine equivalent (SIME) method to perform (and improve) two main important functions of global TSC-OPF approaches: first, SIME is used to efficiently perform the power system transient stability analysis; second, SIME determines a stable one machine infinite bus equivalent rotor angular trajectory that is used as the reference stability constraint, at one specific integration step. In this way, the stability constraint is adjusted by SIME, at each iteration of the TSC-OPF method, in order to accurately reflect power system dynamic behavior. The prowess and main characteristics of the proposed approach are shown by numerical examples.

Load identification in nonintrusive load monitoring using steady-state and turn-on transient energy algorithms

Abstract: Non-intrusive load monitoring (NILM) techniques are based on the analysis of load energy signatures. With characterizing associated transient energy signature, the reliability and accuracy of recognition results can be accurately understood or ascertained. In this study, the computer supported cooperative work techniques (CSCW), artificial neural networks (ANN), in combination with turn-on transient energy analysis, are used to identify loads and to improve recognition accuracy and computational speed of NILM results. The experimental results indicated that the incorporation of turn-on transient energy signature analysis into NILM revealed more information than traditional NILM methods, and the resulting recognition accuracy and computational speed were improved. In addition, in combination with computer supported cooperative work in electromagnetic transient program (EMTP) simulation, calculations of turn-on transient energy facilitated load identification that had significant effect on NILM results.

Rate Transient Analysis in Shale Gas Reservoirs with Transient Linear Behavior

Abstract: Rate Transient Analysis in Shale Gas Reservoirs with Transient Linear Behavior. (May 2009) Rasheed Olusehun Bello, B.Sc., University of Lagos, Nigeria; M.Sc., University of Saskatchewan, Canada Chair of Advisory Committee: Dr. Robert Wattenbarger Many hydraulically fractured shale gas horizontal wells in the Barnett shale have been observed to exhibit transient linear behavior. This transient linear behavior is characterized by a one-half slope on a log-log plot of rate against time. This transient linear flow regime is believed to be caused by transient drainage of low permeability matrix blocks into adjoining fractures. This transient flow regime is the only flow regime available for analysis in many wells. The hydraulically fractured shale gas reservoir system was described in this work by a linear dual porosity model. This consisted of a bounded rectangular reservoir with slab matrix blocks draining into adjoining fractures and subsequently to a horizontal well in the centre. The horizontal well fully penetrates the rectangular reservoir. Convergence skin is incorporated into the linear model to account for the presence of the horizontal wellbore. Five flow regions were identified with this model. Region 1 is due to transient flow only in the fractures. Region 2 is bilinear flow and occurs when the matrix drainage begins simultaneously with the transient flow in the fractures. Region 3 is the response

Extending the Life of Gear Box in Wind Generators by Smoothing Transient Torque With STATCOM

Abstract: Gearboxes for wind turbines must ensure high reliability over a period of 20 years, withstanding cumulative and transient loads. One main challenge to this is represented by electromagnetic torque transients caused by grid faults and disturbances, which will result in significant stresses and fatigue of the gearbox. Possibilities for limiting the torque transients in fixed-speed wind generators have not been previously reported. This paper presents a technique by which the transient torques during recovery after a grid fault can be smoothed in a wind farm with induction generators directly connected to the grid. A model-based control technique using the quasi-stationary equivalent circuit of the system is suggested for controlling the torque with a static synchronous compensator (STATCOM). The basis of the approach consists of controlling the induction generator terminal voltage by the injection/absorption of reactive current using the STATCOM. By controlling the terminal voltage as a function of the generator speed during the recovery process, the electromagnetic torque of the generator is indirectly controlled, in order to reduce the drive train mechanical stresses caused by the characteristics of the induction machine when decelerating through the maximum torque region. The control concept is shown by time-domain simulations, where the smoothing effect of the proposed technique on a wind turbine is seen during the recovery after a three-phase-to-ground-fault condition. The influence of the shaft stiffness in a multimass drive train model is discussed, and the performance of the control concept in the case of parallel connection of several turbines is investigated to discuss the applicability in a wind farm.

Method and system for real-time estimation and prediction of the thermal state of a microprocessor unit

Abstract: A method (and system) of predicting a thermal state of a transient thermal system, includes combining sensor outputs and thermal parameters to construct a consistent set of estimates of internal temperature of a transient thermal system.

Boom or bust? A comparative analysis of transient population dynamics in plants

Abstract: Summary 1. Population dynamics often defy predictions based on empirical models, and explanations for noisy dynamics have ranged from deterministic chaos to environmental stochasticity. Transient (short-term) dynamics following disturbance or perturbation have recently gained empirical attention from researchers as further possible effectors of complicated dynamics. 2. Previously published methods of transient analysis have tended to require knowledge of initial population structure. However, this has been overcome by the recent development of the parametric Kreiss bound (which describes how large a population must become before reaching its maximum possible transient amplification following a disturbance) and the extension of this and other transient indices to simultaneously describe both amplified and attenuated transient dynamics. 3. We apply the Kreiss bound and other transient indices to a data base of matrix models from 108 plant species, in an attempt to detect ecological and mathematical patterns in the transient dynamical properties of plant populations. 4. We describe how life history influences the transient dynamics of plant populations: species at opposite ends of the scale of ecological succession have the highest potential for transient amplification and attenuation, whereas species with intermediate life history complexity have the lowest potential. 5. We find ecological relationships between transients and asymptotic dynamics: faster-growing populations tend to have greater potential magnitudes of transient amplification and attenuation, which could suggest that short- and long-term dynamics are similarly influenced by demographic parameters or vital rates. 6. We describe a strong dependence of transient amplification and attenuation on matrix dimension: perhaps signifying a potentially worrying artefact of basic model parameterization. 7.Synthesis. Transient indices describe how big or how small plant populations can get, en route to long-term stable rates of increase or decline. The patterns we found in the potential for transient dynamics, across many species of plants, suggest a combination of ecological and modelling strategy influences. This better understanding of transients should guide the formulation of management and conservation strategies for all plant populations that suffer disturbances away from stable equilibria.

Non-equilibrium quantum theory for nanodevices based on the Feynman–Vernon influence functional

Abstract: In this paper, we present a non-equilibrium quantum theory for transient electron dynamics in nanodevices based on the Feynman-Vernon influence functional. Applying the exact master equation for nanodevices we recently developed to the more general case in which all the constituents of a device vary in time in response to time-dependent external voltages, we obtained non-perturbatively the transient quantum transport theory in terms of the reduced density matrix. The theory enables us to study transient quantum transport in nanostructures with back-reaction effects from the contacts, with non-Markovian dissipation and decoherence being fully taken into account. For a simple illustration, we apply the theory to a single-electron transistor subjected to ac bias voltages. The non-Markovian memory structure and the nonlinear response functions describing transient electron transport are obtained.

Transient growth analysis of flow through a sudden expansion in a circular pipe

Abstract: Results are presented from a numerical study of transient growth experienced by infinitesimal perturbations to flow in an axisymmetric pipe with a sudden 1-2 diametral expansion. First, the downstream reattachment point of the steady laminar flow is accurately determined as a function of Reynolds number and it is established that the flow is linearly stable at least up to Re=1400. A direct method is used to calculate the optimal transient energy growth for specified time horizon tau, Re up to 1200, and low-order azimuthal wavenumber m. The critical Re for the onset of growth with different m is determined. At each Re the maximum growth is found in azimuthal mode m=1 and this maximum is found to increase exponentially with Re. The time evolution of optimal perturbations is presented and shown to correspond to sinuous oscillations of the shear layer. Suboptimal perturbations are presented and discussed. Finally, direct numerical simulation in which the inflow is perturbed by Gaussian white noise confirms the presence of the structures determined by the transient growth analysis. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3313931]

Methods of Interfacing Rotating Machine Models in Transient Simulation Programs

Abstract: The electromagnetic transient programs (EMTP-like tools) are based on the nodal (or modified nodal) equations that enable an efficient numerical solution and, subsequently, fast time-domain simulations. The state-variable-based simulation programs, such as Simulink, are also used for studying the dynamics of electrical systems. Both the offline and real-time versions of these two types of simulation tools are widely used by the researchers and engineers in industry and academia to study the transient phenomena and dynamics in power systems with rotating electrical machines. This paper provides a summary of the interfacing techniques that are utilized to integrate the general-purpose models of electrical machines with the rest of the power system network for these studies. The interfacing methods are broadly classified as indirect and direct approaches. The paper also describes the numerical properties as well as limitations imposed by the interfacing of the commonly used machine models that should be considered when selecting the simulation parameters and assessing the final results.

Architecture of a Network-in-the-Loop Environment for Characterizing AC Power-System Behavior

Abstract: This paper describes the method by which a large hardware-in-the-loop environment has been realized for three-phase ac power systems. The environment allows an entire laboratory power-network topology (generators, loads, controls, protection devices, and switches) to be placed in the loop of a large power-network simulation. The system is realized by using a real-time power-network simulator, which interacts with the hardware via the indirect control of a large synchronous generator and by measuring currents flowing from its terminals. These measured currents are injected into the simulation via current sources to close the loop. This paper describes the system architecture and, most importantly, the calibration methodologies which have been developed to overcome measurement and loop latencies. In particular, a new ?phase advance? calibration removes the requirement to add unwanted components into the simulated network to compensate for loop delay. The results of early commissioning experiments are demonstrated. The present system performance limits under transient conditions (approximately 0.25 Hz/s and 30 V/s to contain peak phase- and voltage-tracking errors within 5° and 1%) are defined mainly by the controllability of the synchronous generator.

Quadratic Differential and Integration Technique in $V^{2}$ Control Buck Converter With Small ESR Capacitor

Abstract: This paper proposes a quadratic differential and integration (QDI) technique for the design of V 2 control buck converters with small equivalent series resistance (ESR) of the output capacitor. The QDI technique, which eliminates the use of large ESR in the V 2 control structure, achieves the fast transient response with the small output voltage variation in transient period. Besides, the precise sensing signal is derived from the QDI circuit without the unwilling ESR-related distortion. Moreover, the loop analysis demonstrates that the proposed QDI circuit and the proportional and integral compensator can generate the compensation zero pair to stabilize the system. Experimental results show that the output voltage has small voltage ripple opposite to the conventional V 2 control. In load transient period, the overshoot/undershoot voltage is smaller than 40 mV when output voltage is 2 V, and the transient recovery time inheriting the advantage of V 2 control is shorter than 9 ?s with the load step from 100 to 400 mA and vice versa. The highest full chip power conversion efficiency is about 93%.

Modeling the Effects of Electromechanical Coupling on Energy Storage Through Piezoelectric Energy Harvesting

Abstract: This paper focuses on comparing the effects of varying degrees of electromechanical coupling in piezoelectric power harvesting systems on the dynamics of charging a storage capacitor. In order to gain an understanding of the behavior of these dynamics, a transducer whose vibrational dynamics are impacted very little by electrical energy extraction is compared to a transducer that displays strong electromechanical coupling. Both transducers are cantilevered piezoelectric beams undergoing base excitation whose harvested electrical energy is used to charge a storage capacitor. The transient dynamics of the coupled system are studied in detail with an emphasis on their charging power curves and the time to charge the storage capacitor to a specified voltage. An analytic model for the system is derived that takes into consideration the reduction in vibration amplitude of the beam caused by the removal of electrical energy. Although this model makes the typical assumption that the beam is vibrating at its open-circuit resonance, it is shown to predict the charging behavior of the system accurately when compared to experimental results and a complete, nonlinear simulation without this simplification. Finally, the simplifications and discrepancies created by several types of modeling assumptions for a highly coupled energy harvesting system are discussed.

Probabilistic evaluation of transient stability of a power system incorporating wind farms

Abstract: This study presents a stochastic-based approach to evaluate the probabilistic transient stability indices of a power system incorporating wind farms (WFs). In this context, investigations have been conducted on a hypothetical test system representing a typical power system taking into consideration the uncertainties of the factors associated with the practical operation of a power system, namely fault type, fault location, fault impedance, fault clearing process, system parameters and operating conditions and high-speed reclosing process. The effects of the WF sizes and locations on the overall system stability have been investigated. Moreover, this study presents stochastic models for the wind turbine as well as the spring constant of the reduced two-mass shaft model of the wind generator. The time-domain simulations are obtained using the electro-magnetic transient programme.