• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.3
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• pp.275-284
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• 1999

Unbalanced source voltage in the 3-phase power system is decomposed into positive, negative and zero sequence c components. Also, assuming there is no neutral path in the system, the zero sequence component is not shown on the l load side. Therefore, in the unbalanced power system without neutral path. it is possible to provide balanced voltage to t the load side by compensating negative sequence component and also to regulate the voltage amplitude by controlling t the positive sequence component. In addition, the symmetrical components due to voltage unbalance can be effectively d detected on the synchronous reference frame by using dlongleftarrowq transformation. In this paper, an algorithm not only c compensating unbalanced source voltage by canceling the negative sequence component on the synchronous reference f frame but also maintaining load voltages constantly is proposed. Also a novel method for phase angle detection s synchronized by positive sequence component under unbalanced source voltage is suggested and this detected phase a angle is used for d-q transformation. The performances and characteristics of the proposed compensating system are a analyzed by simulation and verified through experimental results.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.5
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• pp.457-465
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• 2011

The fault analysis and detecting algorithm for a 3 phase diode rectifier is proposed. The 3 phase dioderectifier is used for the AC power rectifier of the PWM inverter. The input power or diode faults cause theripples of the DC voltage, degradation of the control performance and life shortening of the DC link capacitor.In this paper, the ripple of the DC voltage is mathematically analyzed for the earth fault of input power andopen circuit fault of the diode, respectively. The fault detection and type of fault can be obtained by comparingthe average DC voltage and the instant DC voltage which is sampled with 6 times of grid frequency. Theproposed method can be easily applicable and doesn't require additional circuit. The experimental and simulationresults are presented to verify the validity of the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.5
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• pp.440-447
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• 2011

This paper deals with supercapacitor energy storage system for the compensation of the slow response characteristics of a fuel cell generation system for grid connection. A bidirectional dc/dc converter is used for the charging and discharging of the supercapacitor. The conventional converters use additional clamping circuit, etc. to reduce a voltage spike at the instant of switching and to provide wide range of soft switching. The proposed method provides simplified hardware implementation without any clamping circuit, and soft switching condition for both charging and discharging mode with proper switching patterns. The usefulness of the proposed scheme is verified through simulation and experimental results with 1 kW system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10A
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• pp.780-787
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• 2003

Adaptive modulation is the method to increase the throughput of the mobile system using the power margin of the system design. In this paper, we propose the method to change adaptive modulation parameters for the stable system operation by monitoring the mobility of the mobile station. The proposed method measures the instanteneous mobility of the mobile station monitoring the closed power control data. The MPSK modulation method is used for the basic modulation method because of the hardware implementation. Using the proposed method we can get the more powerful throughput. By the system simulation to verify the evaluation of the proposed algorithm, we can notice the algorithm is more efficient than the typical method

• The KIPS Transactions:PartD
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• v.15D no.2
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• pp.263-270
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• 2008

Research of ubiquitous computing becomes more popular topic along with the rapid development of wireless technologies. Firstly, research and development on RFID focuses on manufacturing and retail sectors, because it can improve supply chain efficiency. But, it changes to USN (Ubiquitous Sensor Network) by adding a sensor and wireless network technologies on it. In this research, we design and implement the electric facility management service framework to collect real time information of electric facility using RFID/USN. In electric power industry, it is important the supply of energy must be guaranteed. So many power utilities control and supervise the transmission line to avoid power failures. Utilities install many types of sensor to monitor important facilities by wired network such as optical cable and PLC. In this research, we develop the sensor node which is small, easy to install and using wired network. We design the service framework for electric facility management to collect data using RFID tag, reader and wireless sensor nodes and implement the electric facility management service.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.4
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• pp.184-193
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• 2015

Passive Surveillance System based on the TDOA detects the emitter position in the air using TOA of pulses comprising emitter signal from multiple receivers. In case that PRI of pulses from the emitter is not enough big in comparison with the distance among receivers, it causes the ambiguity problem in selecting proper pulse pairs for TDOA emitter geolocation. In this paper, a novel ambiguity resolution method of radar pulses is presented by using genetic algorithm after changing ambiguity problem into optimization problem between TDOA of received pulses from each receiver and emitter position. Simulation results are presented to show the performance of the proposed method.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.4
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• pp.335-343
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• 2017

The Newman-Raju formula and contour integral-based finite element analyses(FEAs) have been widely used to assess crack growth rates and residual lives at crack locations in ships or offshore structures, but the Newman-Raju formula is known to be less accurate for the complicated weld details and the conventional FEA-based contour integral approach needs concentrated efforts to construct FEA models. Recently, an extended finite element method(XFEM) has been proposed to reduce those modeling efforts with reliable accuracy. Stress intensity factors(SIFs) from the approaches such as the Newman-Raju formula, conventional FEA-based J-integral, and XFEM-based J-integral were compared for an infinitely long plate with a propagating elliptic crack. It was concluded that the XFEM approach was far reliable in terms of prediction ability of SIFs. Assuming a 25 year-aged coast guard patrol ship had the prescribed cracks at the bracket toes attached to longitudinal stiffeners in way of deck and bottom, SIFs were derived based on the three approaches. To obtain axial tension loads acting on the longitudinal stiffeners, long term hull girder bending moments were assumed to obey Weibull distribution of which two parameters were decided from a reference (DNV, 2014). For the complicated weld details, it was concluded that the XFEM approach could cost-effectively and accurately estimate the crack growth rates and residual lives of ship structures.

• Journal of Korean Historical Folklife
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• no.26
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• pp.71-106
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• 2008

The objective of this research is to reconstruct an aristocratic officer's travels by analysing Yu, hee-chun's diary, Miamilgi. Yu had kept his diary for eighty three months, from October 1567 to May 1577, and there were twenty six times of travel logs which are analysed in this research. As a result of the analysis, his travels can be divided into official travels and private travels. Sixteen times of official travels were comprised of inspection tours for parishes as a superintendent of Jeonra province, trips to supervise maintenance works of royal tombs and to worship the tombs, to carry out the sanjae (rituals in the mountains) as a second minister of the ministry of rites. It was difficult for him to have private travels as he continually served as a royal officer. He had got only 10 times of private travels during the eighty three months for maintaining the ancestor's tomb and worshiping the ancestors, for recuperating himself and his wife, and for constructing his new house. All of these travels were long-distance ones. In terms of his travel routes, he frequently used royal main trunks, e.g. 'Haenamro' (from Seoul to Damyang), which were maintained by the royal government. The main reason of his frequent using of trunk lines was that convenience facilities such as the royal post stations (Yeok) and royal inns (Won) were equipped well in these roads so it was easy to get horse change services and lodging and boarding. The fact that main trunks were chiefly straight lines and the shortest way was rather secondary reason. On the other hand, when he was a superintendent of Junra province, he had four times of round inspection on all parishes of Junra province, following the tour routs covering all over the province. As he was incumbent royal officer, he started his travel by getting a permission from the king. Simultaneously, he made ready some travel items. Among the items, horse was most important one for the journey. After finishing all the preparing processes before the departure, he had special farewell ceremony for the King, Sookbae, and had a small party with his friends called Jeonbeul. Main transportation means for his travel was horse, and many kinds of horses such as royal government's horse, Yeokma, local government's horse, Swema, as well as his private one were used. Additionally, he used a palanquin while he was doing inspection trip as a superintendent of Junra province. Yu was incumbent officer so he mostly lodged in local government guest houses. If he could not find out any local guest house, he was lodged in royal inn, and in his relatives houses or irregularly in buddhist temples. Most meals were supplied by local royal governments. The activities in his journeys were varied on his travel objectives. In his private journey, it was the main activities that maintaining ancestor's tombs and having a memorial service. During the trip, he visited his relatives. His official trips, on the other hand, had a regularity. Main activities were dealing with public works, and visiting Hyanggyo (country public school). However in the midway, he visited his relatives and had a journey to scenic places.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.95-104
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• 2003

The electric traction systems are quite differ from general power systems which is single-phase and heavy load. Therefore, there are inevitably power quality problems such as steady state or transient voltage drop, voltage imbalance and harmonic distortion. Among these problems, since steady-state volatge drop is the one of most important factor in electric power quality, many researches about on the compensation of volatge drop by using SVC(Static Var Compensator) and/or STACOM(Static Compensator) have been studied and proposed Also, it is expected that transient voltage drop(voltage sag) could affect the control and safety of high speed traction load. In this paper, voltage sag compensation of AT(Auto Transformer) feeding system are studied The detailed transient models of utility source, scott transformer, AT, and traction load are estabilished. The application of DVR(Dynamic Voltage Restorer) in electric traction system is proposed to compensate the voltage sag of traction network which is occured by the fault of utility source. It can be shown that application of the DVR in electric traction system is very useful to compensate the volatge sag from the result of related simulation works.

• Journal of Sensor Science and Technology
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• v.27 no.5
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• pp.317-327
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• 2018

Terahertz (THz) time-domain spectroscopy(TDS), imaging techniques, and related systems have become mature technologies, widely used in many universities and research laboratories. However, the development of creative technologies still requires improved THz application systems. A few key points are discussed, including the innovative advances of mode-locking energy-emitting semiconductor lasers and better photoconductive semiconductor quantum structures. To realize a compact, low cost, and high performance THz system, it is essential that THz spectroscopy and imaging technologies are better characterized by semiconductor and nano-devices, both static and time-resolved. We introduce the THz spectroscopy and imaging systems, the OSCAT(Optical Sampling by laser CAvity Tuning) system and the ASOPS(ASynchronous Optical Sampling) system, are constructed by our research team. We report on the THz images obtained from their use.