• Journal of Power Electronics
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• v.6 no.1
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• pp.52-66
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• 2006

This paper proposes a wind energy conversion system connected to a grid using a self-excited induction generator (SEIG) based on the maximum power point tracking (MPPT) control scheme. The induction generator (IG) is controlled by the MPPT below the base speed and the maximum energy can be captured from the wind turbine. Therefore, the stator currents of the IG are optimally controlled using the indirect field orientation control (IFOC) according to the generator speed in order to maximize the generated power from the wind turbine. The SEIG feeds a (CRPWM) converter which regulates the DC-link voltage at a constant value where the speed of the IG is varied. Based on the IG d-q axes dynamic model in the synchronous reference frame at field orientation, high-performance synchronous current controllers with satisfactory performance are designed and analyzed. Utilizing these current controllers and IFOC, a fast dynamic response and low current harmonic distortion are attained. The regulated DC-link voltage feeds a grid connected CRPWM inverter. By using the virtual flux orientation control and the synchronous frame current regulators for the grid connected CRPWM inverter, a fast current response, low harmonic distortion and unity power factor are achieved. The complete system has been simulated with different wind velocities. The simulation results are presented to illustrate the effectiveness of the proposed MPPT control scheme for a wind energy system. In the simulation results, the d-q axes current controllers and DC-link voltage controller give prominent dynamic response in command tracking and load regulation characteristics.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.606-611
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• 2007

Pulsation is an inherent phenomenon in reciprocating compressors. It interacts with piping to cause vibrations and performance problems. Indiscriminately connecting to a compressor can be dangerous and cost money in the form of broken equipment and piping, poor performance, inaccurate metering, unwanted vibration, and sometimes noise. Piping connected to a compressor can materially affect the performance and response. To minimize these detrimental effects, reciprocating compressor system should be equipped by pulsation suppression system. This study discusses pressure pulsation phenomena occurred in a reciprocating compressor system. An experiment applied air compressor unit, as pulsating pressure generator, has been done. The compressor was connected sequentially to a snubber model and pressure tank. Sensor probes were placed on the inlet and outlet pipes of snubber. Compressor was driven by a motor controlled by a frequency regulator. The experiment was conducted by adjusting the regulator at 40Hz. General information about an internal gas flow can be achieved by numerical analysis approach. Information of the velocity, pressure and turbulence kinetic energy distribution are presented in this paper. Based on this result, the design improvement might be done.

• Journal of the Korea Society of Computer and Information
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• v.12 no.4
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• pp.257-267
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• 2007

Bandwidth Trading(BT) represents a potential market with over 1 trillion USD across the world and high growth potential. BT is also likely to accelerate globalization of the telecommunications industry and massive restructuring driven by unbundling rush. However, systematic researches on BT remain at an infant stage. This study starts with structure analysis of the Internet industry, and discusses significance of Internet interconnection with respect to BT issues. We also describe the bandwidth commoditization trends and review technical requirements for effective Internet interconnection with BT capability. Taking a step further, this study explores the possibility of improving efficiency of network providers and increasing user convenience by developing an architectural prototype of Hub-&-Spoke interconnection model required to facilitate BT. The BT market provides an innovative base to ease rigidity of two-party contract and increase service efficiency. However, as fair, efficient operation by third party is required, this research finally proposes an exchanging hub named NIBX(New Internet Business eXchange).

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.5
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• pp.60-71
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• 2007

The startup characteristic of liquid propellant rocket engine should be focused on the stable ignition of combustion chamber and gas generator. Also, to lessen the propellants consumption during this period which doesn't contribute to the flight thrust, the engine has to be transferred to the nominal mode quickly. Because of the risk of test, it is impossible to develop all the startup cyclogram or the specifications of engine by test, so the precedent numerical approach is quite necessary. In this study we developed a mathematical model for the startup phenomena in a liquid rocket engine driven by gas generator-turbopump system based on the commercial 1-D flow system analysis program, Flowmaster. Using this program we proposed a methodology to obtain the specifications of turbine starter and the opening time of shutoff valves for the stable startup of the engine. To verify this methodology we qualitatively compared the analysis results to the typical startup curve of the published engine, then found it is quite well matched.

• Journal of Digital Convergence
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• v.17 no.12
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• pp.445-450
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• 2019

lock in effect This study aims to examine the viewing pattern of travel vlog on video-sharing platform YouTube. Preliminary survey was conducted with in-depth interviews on the usability and sensibility aspects of creating pleasurable interfaces model. As a result, first, viewers obtains general information on travel using travel vlog. Second, there were difficulties from the informational quantity. Third, the contents marketing using travel vlog could have limitation when it comes to the consistency of product's exposure which common mass media advertisement format have. Improvements driven from this study may provide insight in contents marketing strategy to travel-related companies and provide practical help to creators in contents production.

• Informatization Policy
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• v.20 no.2
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• pp.39-59
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• 2013

Majority of knowledge management(KM) studies in e-government have been confined to facilitate KM within an organization. But due to citizen-centric(citizen-driven) paradigm shift and advance of web 2.0 communication in recent years, KM between governments and citizen in e-government portals is becoming an important consideration. So a series of studies on knowledge enhanced e-government portal get under way by considering that it is necessary to enhance knowledge of e-government portal and assuming it improves the usability of portal. While the topics of knowledge enhancement and e-government(portal) are widely discussed in their own domains there is a paucity of studies that address these constructs in a joint context. This paper aims to propose conceptual framework of knowledge enhanced e-government portal through structuralization of theoretical discussion with holistic approach. This framework presents an evolutional path of knowledge enhanced e-government portal that consists of three phases and it will be used for realizing the knowledge enhanced portal project as a basic reference model.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.4
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• pp.757-764
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• 2018

This paper describes the design and implementation of a 1hp class two-phase type BLDC fan motor used in an air conditioning system. The BLDC motor, which is implemented in this study, is not a commutator motor type with excellent lifetime and durability and is driven by two phase power source. The most important target specification of a motor used in an air conditioning system is that it has a high efficiency at the rated operating point. For this purpose, we designed the stator shape of the BLDC motor, the design of the rotor magnet, and the control circuit for driving. The BLDC motor has a structure where the motor part, the control part, and the power part are integrated. The finite element analysis was used to calculate the characteristics of the BLDC motors, and the conformity of the design results was confirmed by fabricating and testing the prototype model.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.4
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• pp.55-63
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• 2013

This study investigates the trends and uncertainty of the impacts of climate change on paddy rice production in the Geumho river basin. The Long Ashton Research Station stochastic Weather Generator (LARS-WG) was used to derive future climate data for the Geumho river basin from 15 General Circulation models (GCMs) for 3 Special Report on Emissions Scenarios (SRES) (A2, A1B and B1) included in the Intergovernmental Panel on Climate Change (IPCC) 4th assessment report. The Food and Agricultural Organization (FAO) AquaCrop, a water-driven crop model, was statistically calibrated for the 1982 to 2010 climate. The index of agreement (IoA), prediction efficiency ($R^2$), percent bias (PBIAS), root mean square error (RMSE) and a visual technique were used to evaluate the adjusted AquaCrop simulated yield values. The adjusted simulated yields showed RMSE, NSE, IoA and PBIAS of 0.40, 0.26, 0.76 and 0.59 respectively. The 5, 9 and 15 year central moving averages showed $R^2$ of 0.78, 0.90 and 0.96 respectively after adjustment. AquaCrop was run for the 2020s (2011-2030), 2050s (2046-2065) and 2090s (2080-2099). Climate change projections for Geumho river basin generally indicate a hotter and wetter future climate with maximum increase in the annual temperature of $4.5^{\circ}C$ in the 2090s A1B, as well as maximum increase in the rainfall of 45 % in the 2090s A2. The means (and ranges) of paddy rice yields are projected to increase by 21 % (17-25 %), 34 % (27-42 %) and 43 % (31-54 %) for the 2020s, 2050s and 2090s, respectively. The A1B shows the largest rice yield uncertainty in all time slices with standard deviation of 0.148, 0.189 and $0.173t{\cdot}ha^{-1}$ for the 2020s, 2050s and 2090s, respectively.

• Journal of Drive and Control
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• v.13 no.1
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• pp.18-26
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• 2016

This research is conducted to develop an automatic steering system for parallel parking, and the performance of the system was evaluated by parallel parking a conventional vehicle. The automatic steering system consisted of MDPS (motor driven power steering) to control steering, ESC (electronic stability control) to acquire wheel speed, ultrasonic sensors to recognize the parking space, and a controller to communicate and handle data. The parallel parking process using the automatic steering control consisted of parking space recognition, parking path generation, and parking path tracking. The path for parallel parking was generated based on a kinematic model of a conventional vehicle, and a PI controller was used to control the steering angle for path tracking. Parallel parking using the automatic steering control was conducted according to vehicle speed conditions. The results show that the errors on the x-axis and y-axis were below 0.54 m and 0.14 m, respectively, and the error on the steering angle was less than $1^{\circ}$. Therefore, it is possible to implement parallel parking using an automatic steering control system for conventional vehicles.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.6-6
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• 2018

최근 집중 호우로 인한 내수침수 피해가 도시화와 기후변화로 늘어나고 있다. 내수침수 피해로 인한 복구비용과 시간이 증가하고 있으며 향후에는 이보다 더 크게 늘어날 것으로 예상된다. 이러한 문제를 해결하기 위하여 충분한 선행시간을 가지고 내수 침수 구역을 제시할 수 있어야 한다. 기존의 물리적 모델은 정확하고 정교한 결과를 제공하지만, 시뮬레이션을 준비하고 마치는 데에 시간이 많이 소요된다. 그 이유로서는 강우량, 지형적 특성, 배수관망 시스템, 수문학적 매개변수 등의 다양한 데이터도 필요하기 때문이다. 이는 도시유역에 대한 내수침수의 실시간 예측이 어렵게 되었으며, 충분한 선행시간을 확보하지 못하는 원인이 되었다. 본 연구에서는 이 문제에 대한 해결책으로 결정론적 방법과 확률론적 방법을 자료지향형 모형으로 결합하여 해결책을 제시하고자 하며, 특정 강우 조건하에 도시유역에서의 내수침수에 영향을 미치는 맨홀에 대한 정보를 제공하고자 한다. 위와 같은 과정을 수행하기 위하여 입력자료 조합에 대한 비선형 분석을 실시하였으며, 그 결과로 특정 강우 조건에 대하여 각 맨홀에 대한 누적월류량을 예측할 수 있는 비선형 인공신경망을 구축할 수 있었다. 본 연구에서 제시된 방법론은 국내의 강남 배수분구에 대하여 적용이 되었으며, 내수침수 예측결과와 2차원 해석결과를 비교하고자 하였다. 본 연구에서는 위 과정을 통하여 1차원 도시유출해석을 위한 입력 자료를 준비하는 시간을 절약하고, 다양한 강우 조건과 내수침수지도 사이의 연관성을 학습하는 예측 모형을 이용하여 도시유역의 내수침수에 대한 충분한 선행시간을 확보하고자 한다. 결론적으로, 이 연구의 결과는 도시유역에 대한 비구조적 대책 수립에 도움을 줄 것으로 확인이 되며 도시 유역 내에 맨홀 위치들을 고려한 위험지구를 파악하는 데에 유용할 것으로 판단된다.