Equivalent Generator Research Articles

Evaluation of nanofluids performance for simulated microprocessor

In this investigation, deionized water was used as base fluid. Two different types of nanoparticles, namely Al2O3 and Cu were used with 0.251% and 0.11% volumetric concentrations in the base fluid, respectively. Nanofluids cooling rate for flat heat sink used to cool a microprocessor was observed and compared with the cooling rate of pure water. An equivalent microprocessor heat generator i. e. a heated Cu cylinder was used for controlled experimentation. Two surface heaters, each of 130 W power, were responsible for heat generation. The experiment was performed at the flow rates of 0.45, 0.55, 0.65, 0.75, and 0.85 liter per minute. The main focus of this research was to minimize the base temperature and to increase the overall heat transfer coefficient. The lowest base temperature achieved was 79.45 oC by Al2O3 nanofluid at Reynolds number of 751. Although, Al2O3-water nanofluid showed superior performance in overall heat transfer coefficient enhancement and thermal resistance reduction as compared to other tested fluids. However, with the increase of Reynolds number, Cu-water nanofluid showed better trends of thermal enhancement than Al2O3-water nanofluid, particularly at high Reynolds number ranges.

Modeling approaches for considering active distribution grids in power system stability studies

This paper analyzes two different modeling approaches for the dynamic representation of active distribution grids regarding their applicability in power system stability studies. The first one is derived from a coherency-based aggregation method. It represents the distributed generation (DG) by equivalent generators in combination with a static load. The second modeling approach uses a linearized model for representing distribution grids and is named state-space model highlighting its inheriting nature. This approach is expanded by a new strategy considering explicit state limitations. It is shown that this limitation strategy significantly increases the accuracy of the state-space model. Both models are benchmarked against a detailed distribution grid model, and model accuracies are evaluated. The state-space model shows a higher accuracy for voltage dips smaller than 50 %, since all characteristic modes are preserved, and state limitations are represented in detail. For voltage dips above 50 %, the aggregated model may be applied to achieve higher accuracy.

Precise equivalent model of small hydro generator cluster and its parameter identification using improved Grey Wolf optimiser

With the total installed capacity of small hydro generator cluster (SHGC) continues to grow rapidly, the effect of SHGC will have affected to the security and stability of the main network in China, especially to power oscillations of passageway of ultra-high-voltage AC and DC. Thus, a precise equivalent model of SHGC is proposed in this study. In the proposed model, the fifth-order model of generator is adopted as the equivalent generator model, the excitation system is simplified into proportional feedback control model and exponential load model is used as equivalent load model. In addition, Grey Wolf optimiser with chaotic local search is designed to identify the parameters of the equivalent model. Finally, the proposed equivalent technique is applied in one simulation experiment and one practical experiment. The experimental results demonstrate that the validity and accuracy of the proposed equivalent model and identification method in solving dynamic equivalent of SHGC in engineering practice.

Modeling and visualization of the activation wavefront propagation to improve understanding the QRS complex changes indicating left ventricular hypertrophy

Activation wavefront propagation was computed and visualized in a geometrical heart model for pathological cases of reduced velocity of propagation, left ventricular hypertrophy and their combination. Selected parameters of a multiple dipole equivalent heart generator were computed and compared for three heart geometries and several degrees and extents of reduction of propagation velocity.First, the influence of geometrical changes modeling the left ventricular hypertrophy at reference propagation velocity was compared with reduction of the propagation velocity in the reference heart geometry. Reduced propagation velocity yielded similar or greater changes of the magnitude of the (electrical) heart vector representing the activation wavefront than the geometrical changes. Observations of the wavefront propagation with reduced velocity revealed longer presence of a large extent of the wavefront during depolarization which resulted in increased magnitude of the heart vector. The duration of depolarization was significantly prolonged only when the propagation velocity was decreased to 25% of its normal value. Changes of the direction of the maximal heart vector were dependent on the position of the region where the propagation velocity was reduced.Then the combination of the left ventricular hypertrophy and reduced propagation velocity was studied. Such combination enhanced the enlargement of the electrical heart vector and significantly prolonged the duration of depolarization. The influence of reduced activation velocity on the observed parameters was greater than the effect of the enlargement of the left ventricular mass.The presented study showed that intramyocardial conduction disturbances might cause increase of the actual surface area of propagation wavefront leading to changes of the amplitudes of ECG signals comparable with the changes resulting from the left ventricular hypertrophy. Intramyocardial conduction disturbances, as well as the modeled 50% increase of the thickness of the left ventricular wall, did not cause prolongation of the QRS complex out of normal range. Considerable prolongation of the QRS complex duration was observed only for transmural slowing of the propagation velocity to 25% of its reference value in large ventricular areas or for combination of such slowing with the left ventricular hypertrophy.

Stochastic Optimization of Renewable-Based Microgrid Operation Incorporating Battery Operating Cost

Integration of renewable energy resources in microgrids has been increasing in recent decades. Due to the randomness in renewable resources such as solar and wind, the power generated can deviate from forecasted values. This variation may cause increased operating costs for committing costly reserve units or penalty costs for shedding load. In addition, it is often desired to charge/discharge and coordinate the energy storage units in an efficient and economical way. To address these problems, a novel battery operation cost model is proposed which considers a battery as an equivalent fuel-run generator to enable it to be incorporated into a unit commitment problem. A probabilistic constrained approach is used to incorporate the uncertainties of the renewable sources and load demands into the unit commitment (UC) and economic dispatch problems.

Study of silicon pixel sensor for synchrotron radiation detection**Supported by Prefabrication Research of Beijing Advanced Photon Source (R&D for BAPS) and National Natural Science Foundation of China (11335010)

The silicon pixel sensor (SPS) is one of the key components of hybrid pixel single-photon-counting detectors for synchrotron radiation X-ray detection (SRD). In this paper, the design, fabrication, and characterization of SPSs for single beam X-ray photon detection is reported. The designed pixel sensor is a p+-in-n structure with guard-ring structures operated in full-depletion mode and is fabricated on 4-inch, N type, 320 μm thick, high-resistivity silicon wafers by a general Si planar process. To achieve high energy resolution of X-rays and obtain low dark current and high breakdown voltage as well as appropriate depletion voltage of the SPS, a series of technical optimizations of device structure and fabrication process are explored. With optimized device structure and fabrication process, excellent SPS characteristics with dark current of 2 nA/cm2, full depletion voltage < 50 V and breakdown voltage >150 V are achieved. The fabricated SPSs are wire bonded to ASIC circuits and tested for the performance of X-ray response to the 1W2B synchrotron beam line of the Beijing Synchrotron Radiation Facility. The measured S-curves for SRD demonstrate a high discrimination for different energy X-rays. The extracted energy resolution is high (<20% for X-ray photon energy >10 keV) and the linear properties between input photo energy and the equivalent generator amplitude are well established. It confirmed that the fabricated SPSs have a good energy linearity and high count rate with the optimized technologies. The technology is expected to have a promising application in the development of a large scale SRD system for the Beijing Advanced Photon Source.

Cryptographic Properties of Equivalent Ciphers

In this work the use of nonlinear filtering functions applied to Linear Feedback Shift Registers (LFSRs) to generate cryptographic sequences has been studied. Emphasis is on the class of equivalent nonlinear filter generators whose elements produce exactly the same sequence. Given a pair (filtering function, LFSR), the work develops a method of computing equivalent filtering functions applied to different LFSRs, where all these filters generate exactly the same cryptographic sequence. The security of a cipher is that of its weakest equivalent. Thus this article allows one to compute weaker equivalents of apparently secure generators.

Dynamic Equivalents by Modal Decomposition of Tie-Line Active Power Flows

This paper addresses the power system model order reduction proposing an optimal formulation for identifying electromechanical modes present in active power flows. The reduced power system preserves the dynamic and physical characteristics of the studied system. The modal identification is achieved by the digital Taylor–Fourier transform, which decomposes an oscillating signal into monocomponents. Then, these ones are embedded into an objective function with the purpose of estimating the equivalent generators’ parameters. Results demonstrate a reduction in the computational burden and the computing time associated with transient stability studies for the preserved system, retaining its steady-state and dynamic conditions.

A Doob h-Transform of the Gross–Pitaevskii Hamiltonian

We perform a Doob h-transformation of the N-body Hamiltonian for N trapped interacting Bose particles starting from the unique real strictly positive ground state. This identifies the unitarily equivalent Markov generator describing the N interacting diffusion processes. By applying the convergence results coming from the Gross–Pitaevskii (GP) scaling limit to the energy form associated with this Markov generator we obtain the asymptotic generator uniquely corresponding to the GP Hamiltonian, which has been rigorously derived from the N-body Hamiltonian by performing the same scaling limit. Our asymptotic generator is a non linear diffusion generator with a killing rate governed by the GP order parameter. The associated stochastic process properly describes the single particle motion in the Bose–Einstein condensate including the self-interaction which acts here as a probability density-dependent killing rate. Finally, in a one-dimensional setting, we discuss under which conditions the process conditioned to survival converges to a quasi-stationary distribution having density with respect to the speed measure given by the principal eigenfunction of the diffusion generator with killing.

Low-order dynamic equivalent estimation of power systems using data of phasor measurement units

Abstract This paper utilizes data measured by phasor measurement units (PMUs) to extract a low-order dynamic equivalent model for power system stability studies. The estimated model is a 2-order model for synchronous machines. This model has the advantage of simplicity of classical model and considerably reduces the oversimplifying error of classical model. This method offers an alternative approach to analytical model reduction techniques based on the detailed system models. The proposed method uses the synchronized bus voltage and current phasors measured by PMUs. Using post disturbance data, electrical and mechanical parameters of the equivalent generator are estimated sequentially. Furthermore, a new approach for estimation of two-machine and single machine infinite bus (SMIB) equivalent systems are presented for analysis of electromechanical oscillations. To evaluate the performance of the proposed approach, simulations are performed on a two area 13-bus test system and real measured PMU data. Simulation results show that the estimated model can represent the dynamic behavior of the studied system with good approximation.

Impact of reduced inertia on transient stability of networks with asynchronous generation

Summary This paper presents an energy function approach to assess power system transient stability impacts following increased penetration of asynchronous generation plants. Here, the asynchronous windfarm generation is considered as an equivalent conventional synchronous generator with negligible inertia. Assessment had been carried out on three-machine nine-bus test system to compute critical energy and critical fault-clearing time using potential energy boundary surface method. A new representation of plotting contours of critical clearing times on inertia space is presented. This enables estimation of additional inertia required for a network in the event of inertia reduction of other machines. Results of the simulation and new graphical method confirm that transient stability margin of the system reduces with increased penetration of asynchronous generation. Copyright © 2015 John Wiley & Sons, Ltd.

A Fully Nonlinear Compact Modeling Approach for High-Frequency Noise in Large-Signal Operated Microwave Electron Devices

A technology-independent, inherently nonlinear approach is proposed for the compact modelling of high-frequency noise in microwave transistors under large-signal operating conditions. For the compact nonlinear noise model formulation we assume that noise generation can be described by a suitable set of distributed stochastic processes perturbing a very general, non-quasi-static deterministic description of the electron device, in accordance with the strategies adopted in physics-based methods for the choice and exploitation of microscopic diffusion noise sources. The propagation of the internal distributed noise sources up to the intrinsic device terminals leads to a set of non-stationary, correlated equivalent noise generators, nonlinearly controlled by the instantaneous large-signal working point of the device. Starting from a first formulation for the generators, formally derived from a physics-based description of the noise generation mechanisms widely adopted in distributed numerical modeling, mild approximations provide a fully behavioral representation that can be empirically extracted on the basis of measurement data only, and can be easily implemented into commercial computer-aided design tools by means of conventional, uncorrelated noise sources. As far as small-signal (i.e., linear) bias-dependent operation is concerned, it is shown how well-known, widely applied compact models for high-frequency noise can be considered as linearized special cases of the proposed approach. For a full validation, experimental examples are provided, both in small- and large-signal operation, for a GaAs-pHEMT, by considering the case study of a broad-band low-noise amplifier progressively driven into nonlinear regime by an increasing power interferer.

Reliability Analysis of Distribution Network with Integrated Photovoltaic Power Generation

To analyze the influence of distribution network with grid-connected photovoltaic (PV) generation on the power supply reliability, in this paper it firstly regards interconnected PV generation as an equivalent generator with rated capacity as well as the island operation mode of PV to set up a model for reliability calculation and analysis. Based on the network equivalent method, the structure of distribution system with PV is simplified and then the reliability indexes of distribution system are worked out based on Failure Mode and Effects Analysis (FMEA). At last, a comparative calculation between the distribution network with incorporated PV generations and that without PV generations is made. After analyzing a real example, the results suggest that integrating PV power generations reasonably into the distribution network can enhance the reliability of whole distribution system.

Application of UPFC to Enhancing Oscillatory Response of Series-Compensated Wind Farm Integrations

Flexible ac transmission systems, as a key building block of transmission-level smart girds, have shown effective functionalities in promoting the system operation security and service reliability. Facing with series-compensated lines, subsynchronous resonance (SSR) may strike the power system by jeopardizing its stability and mechanical facilities. The operation of such transmission lines is broadening as a direct result of emergent desire to exploit distant wind energy resources in large scales. This paper verifies the capability of unified power flow controller (UPFC) in attenuating SSR in wind farm integrations. SSR is local in its nature; hence, local measurements are merely employed here for controlling the series convertor while wide-area signals could be as well utilized in parallel for other objectives such as inter-area oscillation damping. An equivalent self-excited induction generator (SEIG) represents the wind farm and is connected to the system through a series-compensated line. The UPFC is located at the wind terminal of the linking line; thus, the needed reactive power of SEIG is produced by the shunt branch of UPFC. Both SSR types, namely generator effect and torsional interaction, are examined here. Simulations are carried out on the IEEE first SSR benchmark model integrated with a SEIG wind turbine.

Application of environmental performance assessment of CHP systems with local and global approaches

This paper is focused on methods to indicate the environmental impact in terms of air pollutants of CHP (Combined Heat and Power) systems. The aim is to combine the energy saving achievement with information concerning the environmental benefit, in comparison with the non-CHP scenario.Environmental impact of CHP production both on global and local scale should be taken into account. In particular, the method of the “Avoided Heat Generator” is highlighted in this study as a proper approach for CHP and is used for a local-scale environmental impact evaluation. This approach calculates the reduction of emission due to CHP operation, taking into account the amount of pollutant emitted by an equivalent heat generator, which provides the same thermal power of the CHP prime mover. Moreover, the recommended approach is compared in the paper with another proposed method, based on the PSI (Pollutant Saving Index) value, which is suitable to estimate the global-scale environmental impact.Numerical evaluations of the CHP environmental benefits, in terms of NOx, CO and CO2 emissions, are shown for several CHP systems with different technologies and electric power sizes, in order to provide a comprehensive overview of current CHP prime mover environmental performance and to serve as an application reference example of the two methods potential use, in the framework of the CHP units authorization procedure. The significant effect of the reference comparative scenario is also highlighted.

Rules of Harmonic Longitudinal Propagation in Various Voltage Classes

Different voltage-class buses of transformer substations which are established based on harmonic voltage distortion to limit amplitude via national standards, so study of harmonic longitudinal propagation (RHLP) is essential to power networks. In order to research RHLP, building models of different electrical components which are harmonic sources, equivalent generators, distribution parameter overhead lines (DPOL), transformers, and loads and so on are crucial. This paper proposes a method which utilizes the principle of electric circuits' ohm' law, series resonance and parallel resonance to study RHLP. Finally, according to Henan province power networks frame, a model is constructed in the simulation software packages PSCAD/EMTDC to verify the method. Furthermore, using MATLAB calculation and PSCAD/EMTDC simulation conclude RHLP in different voltage classes.

Development of a linearized photovoltaic generator model for simulation studies with electromagnetic transient programs

Summary In this paper, a linearized equivalent electrical circuit of a photovoltaic generator is developed. The proposed model is based on nonlinear and well-tested current-voltage equations which are however used in an alternative mathematical manner. The application of a linearization process, which differs from the well-known piecewise linear scheme and is based on Taylor's series approximation, leads to uncoupling of the current and voltage quantities in each time step of a digital simulation. Using the proposed equivalent photovoltaic generator circuit, the application of nodal analysis on equivalent resistive circuits derives a photovoltaic system model of linear algebraic equations. This remarkably simplifies photovoltaic systems modeling because one can develop a photovoltaic generator element in electromagnetic transient programs for power systems analysis, of great value to power engineers who are involved in photovoltaic systems modeling. Copyright © 2014 John Wiley & Sons, Ltd.

Operation of a piezoelectric transducer in a voltage generator and current generator circuits

Methods for obtaining all transfer functions of a piezoelectric transducer with allowance for its electrical load were considered. In the emission mode, equivalent voltage and current generators were introduced. In the reception mode, Tevenen’s and Norton’s theorems for equivalent voltage and current generators were used. A comparison of the main formulas obtained with the previously found solutions has shown that the constructed derivation schemes are true. These formulas can be applied to transducers with an arbitrary number of active and passive layers. Recommendations for using the results of this work were presented. These results can be useful in developing both transducers and flaw detectors.

Parameterization of a synchronous generator to represent a full-scale converter generator for fault studies

This paper addresses the representation of the full-scale converter generator technology by equivalent operational impedances valid for short-circuit current calculations. Modern wind power plants are required and designed to ride through faults in the network, subjected to fault clearing. Accurate knowledge of the wind turbine short-circuit current contribution is needed for component sizing and protection relay settings during faults within the wind power plant collector system or in the external networks. The industry standard employs software packages where generators are represented by their equivalent synchronous generator operational impedances, calculated according to standards or for electromagnetic simulation models, when studying fault currents and protection settings for wind power plant installations. Hence, it is of importance to represent non-synchronous wind generators also by an equivalent synchronous generator. The effectiveness of the proposed method has been validated by simulation and site measurements. Copyright © 2013 John Wiley & Sons, Ltd.

Stability Analysis of an Integrated Offshore Wind and Seashore Wave Farm Fed to a Power Grid Using a Unified Power Flow Controller

This paper presents the analyzed results of an integrated offshore wind and seashore wave farm fed to an onshore power grid through a unified power flow controller (UPFC) to simultaneously achieve power-fluctuation mitigation and stability improvement. The performance of the studied offshore wind farm (OWF) is simulated by an equivalent aggregated 100-MW doubly-fed induction generator (DFIG) while the characteristics of the studied seashore wave farm (SWF) are simulated by an equivalent aggregated 60-MW squirrel-cage induction generator (SCIG). A damping controller of the proposed UPFC is designed by using modal control theory to render adequate damping characteristics to the studied system. A frequency-domain approach based on a linearized system model using eigenvalue analysis and a time-domain scheme based on a nonlinear system model subject to disturbance conditions are systematically carried out. It can be concluded from the simulation results that the proposed UPFC joined with the designed damping controller can effectively stabilize the studied integrated OWF and SWF under various disturbance conditions. The inherent power fluctuations injected to the power grid can also be effectively mitigated by the proposed control scheme.