• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.6
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• pp.579-586
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• 2013

This paper proposes a mode transition algorithm between the grid-tied and the stand-alone operations for the single-phase inverter with the energy storage system. For the grid-tied operation, the dc-link voltage and the output current are required to be control. For the stand-alone mode, both the output voltage and the output current should be regulated. In order to mitigate a falling-off in control performance during transients in mode change, the load power estimation and the current selection schemes are proposed. The proposed method allows an optimized current reference is selected to reduce an output voltage drop and an excessive over-current in transient. To verify the effectiveness of the proposed method, both the simulation and the experiments for a 3kW single-phase inverter with the energy storage system have been conducted. From the results, it has been confirmed that the proposed method reduces a transient error as well as implementing smooth mode transition.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.6
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• pp.472-479
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• 2013

A free piston linear engine could be operated under HCCI combustion due to its variable compression ratios. To obtain HCCI combustion, the free piston linear engine needs a high compression ratio to achieve auto-ignition of the fuel/air mixture. In this study, an idea for obtaining a high compression ratio using the transition from SI combustion to HCCI combustion was proposed. The fuel used in this study is hydrogen, which is considered to be an environmentally friendly fuel. Besides, the effects of key parameters such as equivalence ratio (${\phi}$), load resistance ($R_L$) and intake temperature ($T_{in}$) on the SI-HCCI transition were numerically investigated. The simulation results show that the SI-HCCI transition is successful without any significant reduction of in-cylinder pressure as the intake temperature is increased from $T_{in}$=300K (SI mode) to $T_{in}$=450K (HCCI mode), while the load resistance and equivalence ratio are retained respectively at $R_L=120{\Omega}$ and ${\phi}$=0.6 in both SI mode and HCCI mode.

• Proceedings of the Membrane Society of Korea Conference
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• 1993.10a
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• pp.13-20
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• 1993

The sorption equilibria and permeation rates for carbon dioxide in such glassy polymer membranes with high glass-transition temperature as polyimide, polyetherimide, polysulfone and polyethersulfone membranes, were measured. The sorption isotherms for these systems can be described well by the dual-mode sorption model, whereas the pressure dependences of the mean permeability coefficients are simulated better by a modified dual-mode mobility model than the conventional dual-mode mobility model in which the Henry's law and Langmuir populations execute four kinds of diffusive movement.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.578-581
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• 2007

Microplasma modes generated in a display cell with an auxiliary electrode were investigated in accordance with various coplanar-gaps and plategaps. At plate-gaps shorter than the coplanar-gap, the mode transition voltage of the auxiliary pulse increased with an increase in the coplanar-gap. At longer plate-gaps, the mode transition voltage of the auxiliary pulse decreased with an increase in the coplanar-gap.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.334-342
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• 2005

A numerical analysis is performed using two dimensional axisymmetric RANS (Reynolds Averaged Navier-Stokes) equations system on the transition sequence of the Integrated Rocket Ramjet and the unsteady reacting flow-field in a ramjet combustor during unstable combustion. The mode transition of an axisymmetric ramjet is numerically simulated starting from the initial condition of the boost end phase of the entire ramjet. The unsteady reacting flow-field within combustor is computed for varying injection area. In calculation results of the transition, the terminal normal shock is occurred at the downstream of diffuser throat section and no notable combustor pressure oscillation is observed after certain time of the inlet port cover open. For the case of a small injection area at the same equivalence ratio, periodic pressure oscillation in the combustor leads to the terminal shock expulsion from the inlet and hence the buzz instability occurred.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.513-520
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• 2004

A steady-state/transient performance simulation model was newly developed for the propulsion system of the CRW (Canard Rotor Wing) type UAV (Unmanned Aerial Vehicle) during flight mode transition. The CRW type UAV has a new concept RPV (Remotely Piloted Vehicle) which can fly at two flight modes such as the take-off/landing and low speed forward flight mode using the rotary wing driven by engine bypass exhaust gas and the high speed forward flight mode using the stopped wing and main engine thrust. The propulsion system of the CRW type UAV consists of the main engine system and the duct system. The flight vehicle may generally select a proper type and specific engine with acceptable thrust level to meet the flight mission in the propulsion system design phase. In this study, a turbojet engine with one spool was selected by decision of the vehicle system designer, and the duct system is composed of main duct, rotor duct, master valve, rotor tip-jet nozzles, and variable area main nozzle. In order to establish the safe flight mode transition region of the propulsion system, steady-state and transient performance simulation should be needed. Using this simulation model, the optimal fuel flow schedules were obtained to keep the proper surge margin and the turbine inlet temperature limitation through steady-state and transient performance estimation. Furthermore, these analysis results will be used to the control optimization of the propulsion system, later. In the transient performance model, ICV (Inter-Component Volume) model was used. The performance analysis using the developed models was performed at various flight conditions and fuel flow schedules, and these results could set the safe flight mode transition region to satisfy the turbine inlet temperature overshoot limitation as well as the compressor surge margin. Because the engine performance simulation results without the duct system were well agreed with the engine manufacturer's data and the analysis results using a commercial program, it was confirmed that the validity of the proposed performance model was verified. However, the propulsion system performance model including the duct system will be compared with experimental measuring data, later.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.18-20
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• 2008

An electrical balance of plant(EBOP) of a 600kW molten carbonate fuelcell (MCFC) has to transit from grid-connected(GC) mode to grid-independent(GI) mode when a grid is in a fault conditions. A minimum transition time is limited by four cycle for a 600kW MCFC to ride through a grid fault. In this paper, we propose a control algorithm of a 600kW EBOP for a MCFC system. The EBOP has three operation modes, i.e., GC mode, GI mode, and grid-synchronized(GS) mode. The EBOP controls output currents in a GC mode and regulates output voltages in GI or GS mode. GS mode is defined as an interface between GC mode and GI mode to make a mode transition smooth, i.e., limitation of inrush currents, regulation of output voltages within ANSI standard. Simulations and experiments carried out to verify the effectiveness of the proposed control algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.5
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• pp.445-450
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• 2002

We analyzed and measured a CPW(coplanar waveguide)-to-microstrip right-angled transition. Asymmetric CPW-to-microstrip transitions show significant resonances by the slot mode generation at the discontinuities. The air-bridge just shifting the resonance frequency can not fundamentally suppress the occurrence of the slot mode. So, we proposed the structure using offset microstrip section to eliminate the resonance. The proposed structure may be useful for the application of multi-layed structure.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.438-438
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• 2010

The abnormal behavior of the argon metastable density during the E-H mode transition in argon ICP discharge was investigated. Lots of investigations including global models expected that during and after the mode transition of ICP discharge, the density of metastable increases with applied rf power (i.e. electron density). However, recent direct measurement of metastable density revealed that the metastable density of argon decreases with the applied power during and after the mode transition. This result may not be explained by the previous global model which is based on the assumption of the Maxwellian electron energy distribution function (EEDF). In this paper, to explain this abnormal behavior with simple manners, a simple global model taking account of the effect of the non-Maxwellian EEDFs incorporating into a set of coupled rate equations is proposed. The result showed that the calculated metastable density taking account of non-Maxwellian EEDF and its evolution during the transition has an abnormal behavior with electron density and is in good agreement with the previous measurement results, indicating the close coupling of electron kinetics and the behavior of metastable density. The proposed simple model is expected to provide qualitative kinetic insight to understand the behavior of the metastable density in various plasma discharges which typically exhibit non-Maxwellian distribution.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.8
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• pp.790-797
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• 2010

Mode transition of the axi-symmetric screech tone in the low supersonic Mach number range from 1.0 to 1.20 is numerically analyzed. The axi-symmetric Navier-Stokes equations and the k-e turbulence model are solved in the cylindrical coordinate system. The dispersion-relation-preserving(DRP) scheme is applied for space discretization and the optimized four levels marching method are used for time integration. At low supersonic Mach numbers with an axi-symmetric A1 mode in the simulation, it is shown that acoustic propagation due to the nonlinear effects is seen in the lateral direction and the screech tone frequency is the same as the vortex passing frequency due to the generation of intense large-scale vortical motions.