• The Transactions of the Korea Information Processing Society
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• v.7 no.6
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• pp.1753-1765
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• 2000

As the areas of computer application are expanded, real-time application environments that must process as many transactions as possible within their deadlines, such as a stock transaction systems, ATM switching systems etc, have been increased recently. The reason why the conventional database systems can't process soft real-time applications is the lack of prediction and poor performance on processing transaction's deadline. If transactions want to access data stored at the secondary storage, they can not satisfy requirements of real-time applications because of the disk delay time. This paper designs a main-memory database prototype systems to be suitable to real-time applications and then this system can produce rapid results without disk i/o as all of the information are loaded in main memory database. In thesis proposed the improved techniques with respect to logging, checkpointing, and recovering in our environment. In order to improve the performance of the system, a) the frequency of log analysis and redo processing is reduced by the proposed redo technique at system failure, b) database consistency is maintained by improved fuzzy checkpointing. The performance model is proposed which consists of two parts. The first part evaluates log processing time for recovery and compares with other research activities. The second part examines checkpointing behavior.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1902-1915
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• 2017

This paper presents the evaluation of a three-phase three-level DC-DC converter which achieves the soft switching condition for all switches in the circuit and uses the phase-shift PWM strategy to adjust electric power at the output side. According to the analysis, the operation modes can be categorized into two cases: in the first case, where the phase shift angle is less than 120 degrees and in the second case, where the phase shift angle is more than 120 degrees. The outer switches of the circuit operate under ZVS condition and the inner switches operate under ZVZCS condition. It has been discovered that under ZCS condition of the inner switches, when the blocking capacitors decrease, they make the voltage across the blocking capacitor higher so the current reduce rapidly. A three-phase three-level DC-DC converter has a maximum efficiency of 93.5% when its load is of 5.7 kW. The results from the experiment have been compared to the results obtained by the $MATLAB^{(R)}$ simulator in order to confirm the validity of the proposed converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.5
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• pp.518-525
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• 2005

The paper proposes a novel ZVZCS PWM converter. It enables the main switch to be turned on/off with both zero voltage and zero current, the auxiliary switch to be turned on/off with ZCS, the rectifier diode to be turned on/off with ZVS. Moreover, this proposed soft switching technique is suitable for not only minority carrier device but also majority carrier semiconductor device. Since auxiliary resonant circuit of the proposed boost converter is placed out of the main power path, therefore, there are no voltage and current stresses on the main switch and diode. The operation of the proposed boost converter is explained and analyzed theoretical and experimentally, from a prototype operating at 100KHz.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.3
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• pp.222-230
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• 1998

This paper proposes a new gate drive circuit for high power IGBTs which can reduce the harmful effect of reverse recovery current at turn-on and actively suppress the overvoltage across the driven IGBT at turn-off without a snubber circuit. The turn-on scheme decreases the rising rate of the collector current by inereasing the input capacitance at turn-on transient when the gate-emitter voltage goes above threshold voltage. It results in soft transient of the reverse recovery current with no variation in turn-on delay time. The turn-off driving scheme has adaptive feature to the amplitude of collector current, so that the overvoltage can be limited much effectively at the fault collector current. Experimental results under various normal and fault conditions prove the effectiveness of the proposed circuit.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1654-1663
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• 2015

Compared to LC resonance, LCL resonance has distinct advantages such as a large resonant capability, low voltage and current stresses of the power device, constant voltage or current output characteristics, and fault-tolerance capability. Thus, LCL resonant compensation is employed for a movable Inductive Contactless Power Transfer (ICPT) system with a multi-load in this paper, which achieves constant current output characteristics. Peculiarly, the primary side adopts a much larger compensation inductor than the primary leakage inductor to lower the reactive power, reduce the input current ripple, generate a large current in the primary side, and realize soft-switching. Furthermore, this paper proposes an approximate resonant point for large inductor-ratio LCL resonant compensation through fundamental wave analysis. In addition, the PWM control strategy is used for this system to achieve constant current output characteristics. Finally, an experimental platform is built, whose secondary E-Type coils can ride and move on a primary rail. Simulations and experiments are conducted to verify the effectiveness and accuracy of both the theory and the design method.

• Transactions on Electrical and Electronic Materials
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• v.17 no.2
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• pp.79-85
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• 2016

In this study, we proposed a new single-stage small power MH lamp electronic ballast and power-factor correction circuit with improved circuit by the current of passive power factor correction. Main circuit integrates traditional DC/DC and DC/AC circuits into one-stage DC/AC inverter. Moreover, we described the working principle and control strategy of the new circuit; it's soft switching principle; and resonant element parameter design formula. An experimental prototype of HID lamp electronic ballast with output power of 70 W was built to verify the feasibility of the analysis and design. The simulation and experimental results proved that the power factor of this circuit could reach 94%, with efficiency of 90%. The input current harmonics conform to IEC 61000-3-2 standards and its cost is low. These superior performances of the new circuit indicate certain practical values.

• Journal of Power Electronics
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• v.10 no.1
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• pp.85-90
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• 2010

In this paper the effects of a Static Synchronous Series Compensator, which is constructed with a 48-pulse inverter, on the power demand from the grid are studied. Extensive simulation studies were carried out in the MATLAB simulation environment to observe the compensation achieved by the SSSC and its effects on the line voltage, line current, phase angle and real/reactive power. The designed device is simulated in a power system which is comprised of a three phase power source, a transmission line, line inductance and load. The system parameters such as line voltage, line current, reactive power Q and real power P transmissions are observed both when the SSSC is connected to and disconnected from the power system. The motivation for modeling a SSSC from a multi-pulse inverter is to enhance the voltage waveform of the device and this is observed in the total harmonic distortion (THD) analysis performed at the end of the paper. According to the results, the power flow and phase angle can be controlled successfully by the new device through voltage injection. Finally a THD analysis is performed to see the harmonics content. The effect on the quality of the line voltage and current is acceptable according to international standards.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.272-273
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• 2003

Spin dynamics has been investigated intensively in various kinds of fields. Most popular one is an initial permeability at high frequency. Also, magnetic after-effect such as thermal fluctuation of fine magnetic particles and disaccommodation in soft magnetic materials were extensively studied in the past. When we apply an external farce with the same frequency as that of the system being examined, the system absorbs the external energy and the precession enhances. It is called resonance in general. Among the various resonances, ferromagnetic resonance (FMR) has been used as a good tool to evaluate material constants such as saturation manetization or spin damping parameter by analyzing a resonance curve. In this talk first instinctive understanding of Gilbert spin damping and spin pumping will be explained. Then, experimental data for enhancement of Gilbert damping parameter (G) evaluated from FMR spectrum and spin precession measured by a time resolved pump-probe method for Permalloy thin film will be introduced. Finally, magnetization reversal observed by air-coplanar probe will be given.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.5
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• pp.95-100
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• 2011

The next generation IP-PBX system are demanding multimedia facility to carry out UC(Unified Communication) and voice security also. Therefore, in this paper, we have developed the integrated solution of IP-PBX for the voice security by adopting VPN IPsec based on SIP using tunnel method in transmitting voice data to prevent eavesdrop of voice data and have shared between communication system based on PC and PSTN terminals. In particular, We have developed a video conference, private switching, distributed processing and measured telephone conversation quality. This IP-PBX that is connected Soft-phone provide various optional services.

• International Commerce and Information Review
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• v.12 no.4
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• pp.363-382
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• 2010

It should be unthinkable to not provide water at survival of any living things. Water is too a basic element for development for a country. Currently, the global market of mineral water is growing rapidly. This study, I conceptualized mineral water as bottled water. In particularly, bottled water has seen huge global growth for the last few years. The annual growth rate of the market in the period 2005-2009 was 5.9%. Following a surge in obesity and subsequent health and wellness trends, many consumers are switching from sugary soft drinks to healthier alternatives. Therefore, the global bottled water market is one area which has big potential for growth, but price competition is getting intensified among multi-national and domestic firms. Korean providers too are faced with strong competition in growing domestic market. The bottled water market has presence of multinational provider like Nestle, Danone and Coca-Cola, which collectively account for 35.1% of the world market share in 2009. On the basis of a market orientation approach, this article looks at changing environments in the world mineral water industry and attempts to describe foreign market entry strategy of the Korean mineral water industry. The market orientation provides strong norms for learning from customers and competitors, is instrumental in creating a superior value for buyers, innovating successfully, and generating excellent firm performance. So firms should consider a strategic planning in basis on market orientation before they enter foreign markets. Some discussions were made about managerial implications for Korean bottled water providers.