• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.519-521
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• 2000

Network reconfiguration is an operation task, and consists in the determination of the switching operations such to reach the minimum loss conditions of the distribution network. In this paper, an effective heuristic based switch scheme for loss minimization is given for the optimization of distribution loss reduction and a solution approach is presented. The solution algorithm for loss minimization has been developed based on the two stage solution methodology. The first stage of this solution algorithm sets up a decision tree which represent the various switching operations available, the second stage applies a proposed technique called cyclic best first search. Therefore, the solution algorithm of proposed method can determine on-off switch statuses for loss reduction, with a minimum computational effort.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.85-89
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• 1998

A switching power stage is a very nonlinear system because it has two or more operation modes in one switching cycle. To model a switching power stage, the state space averaging method has been developed. Though it allows a unified treatment of a large variety of switching power stages, the model it yields is always very nonlinear. So, it is required to linearize the averaged model. But it is well known that a controller for a nonlinear plant designed by the linearization frequently fails in showing satisfactory control performance. Hence it is very natural to try to design a nonlinear controller for a switching power stage. In design of a switching power system, nonlinear control approaches such as adaptive control and fuzzy control have been widely studied so far. In this research, a recently developed control method, time delay control is briefly studied and a design example for a ZVS PWM half bridge converter is given. The performance of the time delay controller is compared to its conventional counterpart, PI controller by computer simulations.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.3
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• pp.186-190
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• 2005

In this paper, the pipelined A/D converter with multi S/H stage structure is proposed for high resolution and high-speed data conversion rate. In order to improve a resolution and operational speed, the proposed structure increased the sampling time that is sampled input signal. In order to verify the operation characteristics, 20MS/s pipelined A/D converter is designed with two S/H stage. The simulation result shows that INL and DNL are $0.52LSB\~-0.63LSB$ and $0.53LSB\~-0.56LSB$, respectively. Also, the designed Analog-to-Digital converter has the SNR of 43dB and power consumption is 18.5mW.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.5
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• pp.421-425
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• 2008

In this research, a 8-bit CMOS 2 stage folding A/D converter is designed, For low power consumption and small chip size, the A/D converter is designed by using folding and interpolation circuit. Folding circuit is composed of the transistor differential pairs which are connected in parallel. It reduces the number of comparator drastically. The analog block composed of folding block, current interpolation circuit, and three stage current comparator is designed with differential-mode for high speed operation. The simulation in a $0.35\;{\mu}m$ CMOS process. shows DNL and SNDR of 0.5LSB and 47 dB at 250 MHz/s sampling frequency.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.10
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• pp.1523-1527
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• 2015

Traction power is supplied by three-phase alternating current of 154 kV power grid and electric trains are operated on single phase feeding system. It becomes important to use all the three phases equally and convert them into two-phase electric power (90 degree phase rotation) for traction supply. This is achieved by special transformer from the adjacent traction substation which is separated by a neutral section. Neutral section locations are in front of the substation and between the two substations. The first stage of the Seoul-Busan high-speed railway, design curve radius is larger than 7,000 m and the greatest slope is 25‰. The railway track conditions are evaluated as good enough to install a neutral section at the first stage, but a few factors of coasting operation of the train should be considered at the second stage of Seoul-Busan high-speed railway. The neutral section was located at Kim-cheon substation, which made some neutral section problems produced by the operating train, and the neutral section was moved about 1.5 km to the south toward Dong Dae-gu station due to the track operation condition. Some of the trains which stopped at the existing Kim-cheon Gu-mi station produced another motor block failure after moving the neutral section. In this paper, power quality, system performance and track condition, etc. are suggested to solve the problems.

• Journal of Gastric Cancer
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• v.10 no.2
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• pp.63-68
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• 2010

Purpose: Remnant gastric cancer (RGC) are generally detected at advanced stages or infiltration of adjacent organs. We retrospectively reviewed the surgical outcomes and clinicopathologic results of remnant gastric cancers that have operated during fourteen years in one institution of Korea. Materials and Methods: 34 patients who were diagnosed with RGC at Ajou University Hospital from April 1995 to October 2009 were enrolled. We analyzed the features of previous operation, and according to these results, surgical outcomes and clinicopathologic results for RGC were analyzed. Results: Of 34 patients, 20 patients had previously undergone distal gastrectomy for malignant disease, and 14 patients for benign disease. The period between previous operation and surgery for RGC in the patients underwent operation for malignant disease was shorter than that in benign patients (P<0.001). In surgical field, 31 patients (91.0%) were resected and curative resection was possible in 23 patients (67.6%). When 31 patients who underwent resection for RGC were divided into previous malignant and benign disease, there was no significantly different in terms of surgical outcomes and pathologic findings between two groups. Meanwhile, the patients who recently (after 2005) underwent surgery for RGC showed less advanced stage compared with the patients who underwent surgery before 2004. Conclusions: Resection was possible in the higher proportion (91.0%) of patients diagnosed with RGC compared with previous reports. The cause of previous operation did not effect on the surgical outcomes for surgery of RGC. Recent trend of RGC is to increase the proportion of early stage gastric cancer. Therefore, surgeons should consider curatively surgical resection for RGC the regardless of pattern of previous operation.

• Journal of Chest Surgery
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• v.30 no.11
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• pp.1062-1068
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• 1997

From August 1989 to January 1996, a total of 105 cases of bidirectional Glean operations have been done as the interim stage for the patien s with some risk of univentricular correction at Sejong General Hospital. From December 1992, we started the conversion to Fontal operations for them, and 42 cases underwent Fontal-stage operation till February 1996. Their diagnoses were univentricular heart in 19(right ventricular type : 14), tricuspid atresia 11, double outlet of right ventricle 9, and others in 3 cases. The median age of bidirectional Glerln-stage operation was 12.5 months(range 2 months to 8 years) and Fontan-stage operation was at 59.6 months of median age(range 1 year 5 months to ,9 year 7 months). The mean waiting interval between the two operations was 33.88 $\pm$ 17.85 months with a range of 10 months to 6 years 3 months. During the waiting periods, 18 patients developed significant systemic-pulmonary collaterals andfor systemic verso-veno collateral channels. There were 5 hospital deaths after operations due to low cardiac output in 4 and sepsis in one. Most of the Fontal-stage operations were done by the late al tunneling with Core-Tex tube graft patch and fenestrated with the size of 2.5 ~6 mm. All the patients were followed-up(7 months to 4 years 2 months, mean 21.97$\pm$10.82 months) and there were 5 late deaths(postoperatively 6 months to 2 years) due to thromboembolism in 1, after heart transplantation 1, plastic bronchitis 1, protein loosing enteropathy 1, and pneumonia in 1. Dividing the patients by the waiting interval of 2 years, the early correction to Fontal group (N=16) showed the better results(hospital mortality 1116, late mortality 1116, significant collateral development 2/16) compared to the other group(N=26) (4/26, 4/26, 16/26). In conclusion, after the bidirectional Glean-stage operation successfully got rid of the previous risk factors, we recommand to do the Fontan-stage operation no later than 2 years of interval.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.44-54
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• 2014

This paper suggests two kinds of reaction control system command generation methods for upper stage attitude control of launch vehicles. The reaction control system is assumed to consist of two sets of three nozzles. One operation technology is based on mixed attitude error functions, and the other is based on command mixing functions. Both are compared via simulations. The simulation results show that the latter is comparatively preferable in terms of interference among control axes, independency of controller design and analysis among axes, and prediction of flight performance of each control axis.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.5
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• pp.595-604
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• 2016

Utilizing a standard 130-nm CMOS process, a RF frontend is designed at 24 GHz for automotive collision avoidance radar application. Single IF direct conversion receiver (DCR) architecture is adopted to achieve high integration level and to alleviate the DCR problem. The proposed frontend is composed of a two-stage LNA and downconversion mixers. To save power consumption, and to enhance gain and linearity, stacked NMOS-PMOS $g_m$-boosting technique is employed in the design of LNA as the first stage. The switch transistors in the mixing stage are biased in subthreshold region to achieve low power consumption. The single balanced mixer is designed in PMOS transistors and is also realized based on the well-known folded architecture to increase voltage headroom. This frontend circuit features enhancement in gain, linearity, and power dissipation. The proposed circuit showed a maximum conversion gain of 19.6 dB and noise figure of 3 dB at the operation frequency. It also showed input and output return losses of less than -10 dB within bandwidth. Furthermore, the port-to-port isolation illustrated excellent characteristic between two ports. This frontend showed the third-order input intercept point (IIP3) of 3 dBm for the whole circuit with power dissipation of 6.5 mW from a 1.5 V supply.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.5
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• pp.7-14
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• 2011

Currently high power Light Emitting Diode (LED) is in the limelight due to its characteristics of long durability, low maintenance costs, and high efficiency. Furthermore, it does not emit pollutants or poisonous gases and is a light source not using mercury, so it holds a high status in eco-friendly terms as well. In this paper, we studied a two-stage LED power drive circuit that can compensate only voltage regulation through LED output current, in order to improve efficiency of LED drive with constant current control in accordance with changes in temperature. The proposed LED drive has an advantage of reducing LED drive's voltage losses by controlling only voltage change of input power, compared with an existing circuit which controls input voltage. The suggested non-insulation compensating circuit for voltage change was verified to have improved efficiency relative to a LED drive using existing DC/DC converter.