• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.534-535
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• 2009

The objective of this research aims preliminary assessments of the proposed plans of offshore wind farm development based on the recently established national offshore wind map and suitability assessment system of offshore wind farm. Incheon Mueodo, Busan Dadaepo-Gadukdo, Sinangun Haeodo have been assessed considering geographic constraints such as water depth, offshore distance, national park, grid connection, and meteorological constraint such as wind power density and wind direction. According to the assessment, Mueodo plan has a weak point in grid connection and several geographic limitations are involved in Haeodo plan while Dadaepo-Gadukdo seems the most possible plan among the review cases. Because of limited assessment in this research, more detail and further consideration are necessary to make a decision of a feasibility project at proposed sites.

• Journal of Power Electronics
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• v.12 no.2
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• pp.333-343
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• 2012

This paper proposes a strategy of flicker mitigation for doubly-fed induction generator (DFIG) wind turbine systems. In the weak grid system where the grid impedance ratio is low, the reactive power compensation only cannot suppress the flicker sufficiently due to the limited power capacity of the converters or the DFIG. For the full suppression of flickers, the active power smoothening using the energy storage system (ESS) needs to be utilized together with the reactive power compensation. The effectiveness of the proposed method is verified by PSCAD/EMTDC simulation results for a 2[MW] DFIG wind turbine system and by experimental results for a 3[kW] wind turbine simulator.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.10
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• pp.805-811
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• 2000

Reliability of PBGA(plastic ball grid array) package is weak compared with normal plastic packages. The low reliability is caused by low resistance to the popcorn cracking, which is generated by moisture absorption in PCB(prited circuit board). In this paper, plasma treatment process was used and we analyzed its effects to interface adhesion. The contents of C and Cl decrease after plasma treatment but those of O, Ca, N relatively increase. The plasma treatment improves the adhesion between EMC(epoxy molding compound) and PCB(solder mask). The grade of improvement was over 100% Max, which depends on the properties of EMC. The RMS(root mean square) roughness value of the solder mask surface increases to plasma treatment. There is little difference of adhesion in RF power and treatment time.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.206-207
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• 2016

The intermittent characteristics of wind power (WP) may have negative effect on grid stability, especially in weak grid. WP fluctuation rate can be reduced by using energy storage system (ESS) through charging and discharging. The operation of ESS will decide its losses and lifetime of batteries. From this point, this paper proposes WP smoothing control by using short-term average of WP. In this case, the ESS will only operate at high WP fluctuation rate. Then, the output power of ESS will be estimated by short-term average value. The effectiveness of proposed method will be verified by comparing with conventional method. The simulation results will be carried out by using Matlab program.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.222-222
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• 2000

PBGA(Plastic Ball Grid Array) is composed of some materials such as PCB(Printed Circuit Board), epoxy molding compound, die attach and so on. Reliability of PBGA package is weak compared with plastic packages. The weak points of reliability are the lower resistance to popcorn cracking, which is induced by moisture absorption in PCB, and the pressure cooker test corrosion, which is the basic problem due to the material characteristics of PCB. Introducing the PCB baking and the plasma treatment cleared the popcorn cracking phenomenon. The PCB baking and plasma treatment reduced the epoxy void by eliminating the source of moisture vaporization during the epoxy curing and enhanced the adhesion between PCB and epoxy. Also, plasma treatment enhanced the wettability of epoxy on PCB. The problem of corrosion is cleared using multi-functional epoxy. This type of EMC(Epoxy Molding Compound) is recommended in package using PCB as a substrate. (Received November 19, 1999)

• Journal of Welding and Joining
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• v.18 no.2
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• pp.95-99
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• 2000

PBGA(Plastic Ball Grid Array) is composed of some materials such as PCB(Printed Circuit Board), epoxy molding compound, die attach and so on. Reliability of PBGA package is weak compared with plastic packages. The weak points of reliability are the lower resistance to popcorn cracking, which is induced by moisture absorption in PCB, and the pressure cooker test corrosion, which is the basic problem due to the material characteristics of PCB. Introducing the PCB banking and the plasma treatment cleared the popcorn cracking phenomenon. The PCB banking and plasma treatment reduced the epoxy void by eliminating the source of moisture vaporization during the epoxy curing and enhanced the adhesion between PCB and epoxy. Also, plasma treatment enhanced the wettability of epoxy on PCB. The problem of corrosion is cleared using multi-functional epoxy. This type of EMC(Epoxy Molding Compound) is recommended in package using PCB as a substrate.

• Journal of Korea Multimedia Society
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• v.9 no.12
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• pp.1542-1551
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• 2006

In the Grid Database, some replicas will have more requests from the clients than others. A fast consistency algorithm has been presented to satisfy the high demand nodes in a shorter period of time. But it has poor performance in multiple regions of high demand for forming the island of locally consistent replicas. Then, a leader election method is proposed, whereas it needs much additional cost for periodic leader election, information storage, and message passing, Also, false leader can be created. In this paper, we propose a tree-based algorithm for replica update propagation. Leader replicas with high demand are considered as the roots of trees which are interconnected. All the other replicas are sorted and considered as nodes of the trees. Once an update occurs at any replica, it need be transmitted to the leader replicas first. Every node that receives the update propagates it to its children in the tree. The update propagation is optimized by cost reduction for fixed propagation schedule. And it is also flexible for the dynamic model in which the demand conditions change with time.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.11
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• pp.717-723
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• 1999

The transient characteristics of grounding systems play a major role in the protection of power equipments, electronic circuits and info-communication facilities against surges which arise from lightning or ground faults. Electronic devices are very weak against lightning surges injected from grounding systems and can be damaged. The malfunction and damage of electronic circuits bring about bad operation performances, a lot of economical losses, and etc. Therefore, in order to obtain the effective protection measure of electronic devices from overvoltages and lightning surges, the analysis of the transient grounding impedances in essential. One of this work is to examine the transient behaviors of grounding impedances under steplike currents for various grounding systems. And the other of this work is to evaluate the transient behaviors of a grid with rods under impulse currents and to investigate the effect of grounding lead wire. Transient grounding impedances of a grid with rods under impulse current waves have been measured as a parameter of the length of the grounding leads. Z-t, Z-i and V-i curves of transient grounding impedance under impulse current waveforms have been measured and analyzed. It was found that the grounding impedance gives the inductive, resistive and capacitive aspects under steplike current. Transient grounding impedance characteristics were very different with shapes, geometries of ground electrodes. Also, they were dependent on the waveform and magnitude of impulse current.

• Journal of Power Electronics
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• v.18 no.6
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• pp.1844-1854
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• 2018

Isolated power systems (IPS) are often characterized by a weak grid due to small power grids. The grid side voltage is no longer equivalent to an ideal voltage source of an infinitely big power grid. The conversion control of new energy sources, parameter perturbations as well as the load itself can easily cause the system voltage to oscillate or to become unstable. To solve this problem, increasing the energy-storage power sources is usually used to improve the reliability of a system. In order to provide support for the voltage, the energy-storage power source inverter needs an method to control the voltage source. Therefore, this paper has proposed the active damping control of a voltage source inverter (VSI) based on virtual compensation. By simplifying the VSI double closed-loop control, two feedback compensation channels have been constructed to reduce the VSI output impedance without changing the characteristics of the voltage gain of a system. This improvement allows systems to operate stably in a larger range. A frequency-domain analysis, and simulation and experimental results demonstrate the feasibility and effectiveness of the proposed method.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.203-208
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• 2007

Due to the long tectonic history and the very complex geologic formations in Korea, the anisotropic characteristics of subsurface material may often change very greatly and locally. The algorithms for the travel time computation commonly used, however, may not give sufficiently precise results particularly for the complex and strong anisotropic model, since they are based on the two-dimensional (2D) earth and/or weak anisotropy assumptions. This study is intended to develope a three-dimensional (3D) modeling algorithm to precisely calculate the first arrival time in the complex anisotropic media. We assume 3D TTI (tilted transversely isotropy) medium having the arbitrary symmetry axis. The algorithm includes the 2D non-linear interpolation scheme to calculate the traveltimes inside the grid and the 3D traveltime mapping to fill the 3D model with first arrival times. The weak anisotropy assumption, moreover, can be overcome through devising a numerical approach of the steepest descent method in the calculation of minimum traveltime, instead of using approximate solution.