• KIEE International Transactions on Power Engineering
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• v.3A no.1
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• pp.17-26
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• 2003

In this paper, the comparative steady-state operating performance analysis algorithms of the stand-alone single-phase self-excited induction generator (SEIG) is presented on the basis of the two nodal admittance approaches using the per-unit frequency in addition to a new state variable de-fined by the per-unit slip frequency. The main significant features of the proposed operating circuit analysis with the per-unit slip frequency as a state variable are that the fast effective solution could be achieved with the simple mathematical computation effort. The operating performance results in the simulation of the single-phase SEIG evaluated by using the per-unit slip frequency state variable are compared with those obtained by using the per-unit frequency state variable. The comparative operating performance results provide the close agreements between two steady-state analysis performance algorithms based on the electro-mechanical equivalent circuit of the single-phase SEIG. In addition to these, the single-phase static VAR compensator; SVC composed of the thyristor controlled reactor; TCR in parallel with the fixed excitation capacitor; FC and the thyristor switched capacitor; TSC is ap-plied to regulate the generated terminal voltage of the single-phase SEIG loaded by a variable inductive passive load. The fixed gain PI controller is employed to adjust the equivalent variable excitation capacitor capacitance of the single-phase SVC.

• Journal of Electrical Engineering and Technology
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• v.12 no.3
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• pp.1090-1100
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• 2017

This paper presents the comparison of starting current characteristics of a three-phase induction motor fed by two types of soft starters. The first soft starter under investigation is a conventional AC voltage controller on the basis of a phase-control technique. The other is the proposed asynchronous PWM AC chopper which is developed from the conventional synchronous PWM AC chopper. In this paper, the proposed asynchronous PWM AC chopper control scheme is developed by generating only two asynchronous PWM signals for a three-phase main power circuit (6 switching devices) from a single voltage control signal which is compared with a single sawtooth carrier signal. By this approach, the PWM signals are independent and easy to implement since the PWM signals do not need to be synchronized with a three-phase voltage source. Details of both soft starters are discussed. The experimental and simulation results of the starting currents are shown. It is found that the asynchronous PWM AC chopper efficiently works as a suitable soft starter for the three-phase induction motor due to that the starting currents are reduced and are sinusoidal with less harmonic contents, when being compared with the starting current waveforms using the conventional phase-control starting technique. Also the proposed soft starter offers low starting electromagnetic torque pulsation.

• Journal of Electrical Engineering and Technology
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• v.7 no.4
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• pp.570-575
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• 2012

In a wireless communication RF transmitter, the output of a quadrature modulator (QM) is distorted by not only the linear imperfection features such as in/quadrature-phase (I/Q) input gain imbalance, local phase imbalance, and local gain imbalance but also the nonlinear imperfection features such as direct current (DC) offset and mixer nonlinearity related to in-band spurious signal. In this paper, we propose the unified QM model to analyze the combined effects of the linear and nonlinear imperfection features on the performance of the QM. The unified QM model consists of two identical nonlinear systems and modified I/Q inputs based on the two-port nonlinear mixer model. The unified QM model shows that the output signals can be expressed by mixer circuit parameters such as intercept point and gain as well as the imperfection features. The proposed approach is validated by not only simulation but also measurement.

• Journal of computational fluids engineering
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• v.15 no.1
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• pp.9-16
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• 2010

The characteristics of flow and heat transfer in a bubbling fluidized bed are investigated by means of computational fluid dynamics (CFD). To simulate two-phase flow for the gas and solid flows, Eulerian-Eulerian approach is applied. Attention is paid for a heat transfer from the wall to fluidized bed by bubbling motion of the flow. From the result, it is confirmed that heat transfer is promoted by chaotic bubbling motion of the flow by enhancement of mixing among solid particles. In particular, the vortical flow motion around gas bubble plays an important role for the mixing and consequent heat transfer. Discussion is made for the time and space averaged Nusselt number which shows peculiar characteristics corresponding to different flow regimes.

• Korean Management Science Review
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• v.26 no.3
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• pp.101-115
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• 2009

In this paper, we propose a technology mining framework for mobile communication industry. We develop a two phase approach of new technology identification and service enhancement. The new technology identification process consists of R&D issues analysis, technology theme design, and emerging technology sampling. On the other hand, existing service enhancement process has technology landscaping, keyword based search, and technological growth analysis. By implementing these two phase frameworks, we develop a technology portfolio for mobile communication industry.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.463-468
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• 1997

This paper presents a theoretical approach of the instability criterion from stratified to nonstratified flow in horizontal pipe at cocurrent flow conditions. The new theoretical instability criterion for the stratified and nonstratified flow transition in horizontal pipe has been developed by hyperbolic equations in two-phase flow, Critical flow condition criterion and onset of slugging at cocurrent flow condition correspond to zero and imaginary characteristics which occur when the hyperbolicity of a stratified two-phase flow is broken, respectively. Through comparison between results predicted by the present theory and the Kukita et al.[1] experimental data of pipes, it is shown that they are in good agreement with data.

• Journal of Power Electronics
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• v.11 no.5
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• pp.655-661
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• 2011

This paper presents two topologies for single-stage single-phase double-buck type PFC converters, designed to operate at high power factor, near sinusoidal input currents and adjustable output voltage. Unlike the known buck type PFC topologies, in which the output voltage is always lower than the maximum input voltage, the proposed converters can operate at output voltages higher than the ac input peak voltage. A reduced number of switches on the main path of the current are another characteristic of the two proposed topologies. To shape the input line currents, a fast and robust controller based on a sliding mode approach is proposed. This active non-linear control strategy, applied to these converters allows high quality input currents. A Proportional Integral (PI) controller is adopted to regulate the output voltage of the converters. This external voltage controller modulates the amplitude of the sinusoidal input current references. The performances of the presented rectifiers are verified with experimental results.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.438-440
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• 2003

This study is introducing a new approach of ATInSAR hologram for modeling wave refraction spectra pattern. TOPSAR data with L$_{-HH}$ and C-vv bands utilized spatial variation of wave refraction. Based on the phase information in along track interferometry, and ATInSAR hologram the quantitative information such swell wave height and spectra energy have been modeled. The phase information in ATInSAR hologram images can be transferred to wave refraction The ATInSAR hologram can be used to investigate the wave refraction pattern along the coastal waters. The fringe information pattern was shown to be useful in modeling wave refaction spectra varaition. The hologram interferometry wave refraction model consists of two sub-models. The purpose of first sub-model is to determine the swell wave height by using ATInSAR. Second sub-model aims to generate the holographic interferometry from the information of two wave spectra which detected by ATInSAR technique. The azimuth cut-off variations along the fringe patterns will be estimated. As azimuth cut-off contains the wave height information which could be used the significant wave height variation in convergence and divergence zone.

• Advances in materials Research
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• v.12 no.2
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• pp.101-118
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• 2023

The purpose of this paper is to study the effects of magnetic field and gravitational field on fiber-reinforced thermoelastic medium with memory-dependent derivative. Three-phase-lag model of thermoelasticity (3PHL) is used to study the plane waves in a fiber-reinforced magneto-thermoelastic material with memory-dependent derivative. A gravitating magneto-thermoelastic two-dimensional substrate is influenced by both thermal shock and mechanical loads at the free surface. Analytical expressions of the considered variables are obtained by using Laplace-Fourier transforms technique with the eigenvalue approach technique. A numerical example is considered to illustrate graphically the effects of the magnetic field, gravitational field and two types of mechanical loads(continuous load and impact load).

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.1152-1166
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• 2023

The bubbly flow of air or steam in subcooled water are investigated here in several test cases, characterized by different pipe sizes, bubble dimensions and flow rates, by means of CFD using a Eulerian-Eulerian approach. The performance of models that differ for the turbulence closure in the continuous phase, as well as for the description of the lift force on the dispersed phase, are compared in detail. When air is considered, the space of the experimental parameters leading to a reasonable performance for the selected models are identified and discussed, while the issues left in the modelling of the concurrent condensation are highlighted for the cases where steam is used.