• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.4
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• pp.364-372
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• 2016

In this paper, a voltage controller for the seamless transition of a grid-connected inverter for ESS is proposed. The single-phase inverter is operated as a current controller when the grid is connected and as a voltage controller in the stand-alone mode when the grid is disconnected. Generally, in the case of grid recovery, the overcurrent may flow into the system because of the mismatch phase between the inverter output and grid voltages. The proposed controller resolves the overcurrent problem through phase delay problems with initial value feed-forward control of the integrator when the grid voltage is restored. The effects of the control method are simulated through PSIM, and the usefulness of the control method is verified through experiments.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.95-96
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• 2016

This paper presents a voltage and frequency droop control for accurate power sharing of parallel distributed generation (DG) inverters in low voltage microgrid. In practice, line impedances between inverters and the point of common coupling of a microgrid are not always equal. This inequality in line impedances often results in reactive power sharing mismatch among inverters. To address this problem, intensive researches have been conducting. Although these methods can solve the unbalanced reactive power sharing, there are still problems remain unresolved, such as complicated structure or circulating current. To overcome such problems, a new droop control scheme is proposed, which not only guarantees accurate reactive power sharing but also has simple structure so that it can be easily implemented in existing systems without any hardware modification. The simulation is performed using Matlab/Simulinks to validate the proposed scheme.

• Journal of Korea Port Economic Association
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• v.21 no.4
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• pp.55-74
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• 2005

This study focuses on affording a material basis for rearranging the manpower supply system in port and logistics industry for Busan's international competitiveness strategies. First of all, the current state and future plan of port and logistics industry, as Busan's main strategic industry, are reviewed. Then theoretical background are introduced for the estimate of demand. As a methodology of this research, Cubic model is applied to estimate the demand of manpower by using 10 year time series data from 1993 to 2002. This paper also surveyed the supply side of port and logistics industry manpower in Busan area. The amounts of mismatched equilibrium between the demand and the supply are measured in this study. The concluding remarks shows some suggestions for the problem of mismatch and the relating policy planning.

• New & Renewable Energy
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• v.6 no.1
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• pp.38-45
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• 2010

Abstract Under the physical stress on photovoltaic (PV) module, it will be warped according to elongation of the front glass and then micro-crack will be occurred in the thermally sealed solar cell. This micro-crack leads to drop of short circuit current of the PV module. This is because of increase of resistance component by micro-crack. Micro-crack at specific solar cell in the module lessens the durability of PV module with reduced output, hot-spot caused by solar cell output mismatch and increased resistance component. This study shows the relation between electrical characteristics and micro- cracks due to mechanical stress on PV module.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.5
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• pp.737-746
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• 1990

Ga0.47In0.53As PIN photodiodes(PD) having various areas have been fabricated by liquid phase epitaxial techniques. Ternary melt has been baked out at 675\ulcorner in H2 atmosphere for 20 hours before growth, which resulted in reduction of background carrier concentration of grown epi-layer. Also, lattice mismatch has been controlled within 0.01%. The room temperature performance of 10**-4cm\ulcornerarea PIN PD at a bias voltage of -5V were` quantum efficiency(with no antireflection coating)=60% for 1.3\ulcorner light source, dark current\ulcorner5nA, and capacitance\ulcornerpE. Frequency response measurement of packaged PIN PD has shown that cut-off frequency (f-3dB) was 961MHz. This PD has shown a good eye pattern when it was incorporated in a 565Mbps optical receiver.

• Culinary science and hospitality research
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• v.14 no.4
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• pp.27-40
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• 2008

This study focused on retraining programs for cuisiniers and drawing attention to the necessity of retraining and the new method of retraining for cuisiniers as a professional in a knowledge based society. Case study review and interviews followed by thorough review of related literatures were taken place to give suggestions and comments for the improvement of job performance enhance training for cuisiniers. Interviews were done with current participants and institutional trainers in March, 2008. Result from the interviews showed that retraining was really necessary. It was concluded that various retraining programs organized and developed by an association could be the solution. Methods of retraining can take formats of distance learning, classroom learning, and blended learning. However, working condition for most cuisiniers at present would allow them to squeeze some time off to attend higher education and most restaurant companies are not big enough to offer systematic job training on site or not stable enough to arrange replacement workers. It is therefore suggested to adopt a blended learning method and further study on this subject is highly recommended.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.12
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• pp.16-22
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• 1994

In this paper, transmitter and receiver modules for free space optical interconnection are implemented and characterized. In the transmitter module, bias circuitry which inject current into the direct modulated laser diode is fabricated and in the receiver module, p-i-n diode is integrated with an MMIC amplifying stage. Laser diode has a direct-modulated bandwidth of 2 GHz at 1.4 Ith bias while p-i-n diode and amplifying stage has a bandwidth of 1.3 GHz and 1.5 GHz, repectively. Optical interconnection has a bandwidth of 1.3 GHz and linearly transmit modulated voltage signal up to 1.5 Vp-p. Measured loss of optical interconnection is 5dB which is composed of optoelectronic conversion loss of 15 dB, electrical impedance mismatch loss of 6.7 dB in transmitter module and gain of 18 dB in receiver module. Seperation between transmitter and receiver can be extended up to 50 cm by using a lens.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.492-492
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• 2014

On account of the good conductivity and optical properties, TCO is generally used in silicon heterojunction solar cell since the emitter material, hydrogenated amorphous silicon (a-Si:H), of the solar cell has low conductivity compare to the emitter of crystalline silicon solar cell. However, the work function mismatch between TCO layer and emitter leads to band-offset and interfere the injection of photo-generated carriers. In this study, work function engineering of TCO by oxygen reactive sputtering method was carried out to identify the trend of band-offset change. The open circuit voltage and short circuit current are noticeably changed by work function that effected from variation of oxygen ratio.

• Journal of Power Electronics
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• v.18 no.3
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• pp.826-840
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• 2018

This paper presents a distributed maximum power point tracking (DMPPT) algorithm based on the reference voltage perturbation (RVP) method for the PV modules of a series PV string. The proposed RVP-DMPPT algorithm is developed to accurately track the maximum power point (MPP) for each PV module operating under all atmospheric conditions with a reduced hardware overhead. To study the influence of parameters such as the controller reference voltage ($V_{ref}$) and PV current ($I_{pv}$) on the PV string voltage, a small signal model of a unidirectional differential power processing (DPP) based PV-Bus architecture is developed. The steady state and dynamic performances of the proposed RVP DMPPT algorithm and small signal model of the unidirectional DPP based PV-Bus architecture are demonstrated with simulations and experimental results. The accuracy of the RVP DMPPT algorithm is demonstrated by obtaining a tracking efficiency of 99.4% from the experiment.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.65-66
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• 2000

Various fluoride films on a glass substrate were prepared and characterized to provide a seed layer for crystalline Si film growth. The XRD analysis on $CaF_2/glass$ illustrated (220) preferential orientation and showed lattice mismatch less than 5 % with Si. We achieved a fluoride film with breakdown electric field of 1.27 MV/cm, leakage current density about $10^{-6}$ $A/cm^2$, and relative dielectric constant less than 5.6. This paper demonstrates microcrystalline silicon $({\mu}c-Si)$ film growth by using a $CaF_2/glass$ substrate. The ${\mu}c-Si$ films exhibited crystallization in (111) and (220) planes, grain size of $700\;{\AA}$, crystalline volume fraction over 65 %, dark- and photo-conductivity ratio of 124, activation energy of 0.49 eV, and dark conductivity less than $4{\times}10^{-7}$ S/cm.