• 전력전자학회논문지
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• 제23권2호
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• pp.94-100
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• 2018

Generally, in a single-phase energy storage system (ESS) for households, AC ripple component with twice the fundamental frequency exists inevitably in the DC link voltage of single-phase PCS. In the grid-connected mode of a single-phase inverter, the AC ripple component in the DC link voltage causes low-order harmonics on grid-side current that deteriorates power quality on an AC grid. In this work, a control system adopting a feedforward controller is established to eliminate the AC ripple interference on the DC link side. Optimal battery nominal voltage design method is also proposed by considering the voltage loss and AC ripple voltage on DC link side in a single-phase ESS. Finally, the control system and battery nominal voltage design method are verified through simulations and experiments.

• Journal of electromagnetic engineering and science
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• 제16권2호
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• pp.80-86
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• 2016

This paper proposes the algorithm for forward link adaptive coding and modulation (ACM) and the detailed design for a satellite communication system to improve network reliability and system throughput. In the ACM scheme, the coding and modulation schemes are changed by as much as the channel can provide depending on the quality of the communication link. To implement the forward link ACM system in the Ka-band, channel prediction and modulation/coding decision methods are proposed and simulated. The parameters of the adaptive filter predictor based on the least mean square are optimized, the minimum mean square error of the channel predictor is 0.0608 when step size and the number of filter tap are 0.0001 and 4, respectively. A test-bed is set up to verify the forward link ACM system, and a test is performed using a Ka-band satellite (i.e., Communication, Ocean, and Meteorological Satellite [COMS]). This test verifies that the ACM scheme can increase the system throughput.

• 정보과학회 컴퓨팅의 실제 논문지
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• 제22권5호
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• pp.235-239
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• 2016

커밋-버그 링크는 커밋히스토리(commit history)와 버그 리포트(bug report) 간의 연결(Link)을 뜻한다. 커밋-버그 링크는 소프트웨어 유지보수와 결함 예측, 버그 추적 시스템(Bug Tracking System)에 이용이 되며, 특히 결함 예측 측면에서는 성능면에서의 기반이 된다. 일반적으로 링크를 자동으로 연결하는 방식은 텍스트 유사도(text similarity)나 시간 간격(time interval), 키워드(keyword) 등을 통해서 추출하였다. 하지만 기존 방식은 커밋히스토리(commit history)의 질적인 부분에 의존적이기 때문에 다수의 링크를 놓치게 된다는 단점이 존재한다. 본 논문에서는 커밋히스토리의 메시지(message)부분에만 의존하지 않고, 버그리포트에서 연결된 커밋히스토리의 파일간의 유사도를 이용하여 링크를 연결할 수 있는 방식을 제안하고 실험을 통하여 본 기법의 적용성을 보인다.

• 전력전자학회논문지
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• 제17권5호
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• pp.377-387
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• 2012

A single-phase grid-connected PV system is known as suitable for housing of less than 3 kW. The DC link voltage in a single-phase PV system has necessarily twice component of fundamental wave. It makes high THD in the grid current. According to the problem, power quality is lower. Many engineers have studied about this problem. The most simple method is to use low pass filter on DC link voltage control. However it is affected by DC link voltage control bandwidth. If cutoff frequency is reduced to increase the performance of low pass filter, it also lowers DC link voltage control bandwidth. Second method is using band stop filter, it works good on steady state but not good on transient state. This paper proposes the new method for removing ripple voltage to get an exact current reference. It improves the responses on steady state and transient state. The performance was verified through computer simulation using MATLAB and actual experiments.

• Current Optics and Photonics
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• 제5권2호
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• pp.114-120
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• 2021

Free-space optical (FSO) communication is considered to be a potential solution to congestion in the radio-frequency spectrum and last-mile-access bottleneck issues in future cellular communication networks, such as 5G and beyond. However, FSO link performance may degrade significantly due to irradiance fluctuations and random temporal fluctuations from atmospheric turbulence. Therefore, in this work the main objective is to reduce the effect of the atmospheric turbulence by considering a multihop FSO communication system with amplify-and-forward relaying supported by a radio-frequency (RF) link, which form a hybrid FSO/RF communication system. The FSO link is assumed to follow the gamma-gamma fading model, which represents strong turbulence. Also, the RF link is modeled by a Rayleigh distribution. The performance of the considered system, in terms of the outage probability and average bit-error rate (BER), is investigated and analyzed under various weather conditions and pointing errors. Furthermore, the effect of the number of employed relay nodes on the performance of the system is investigated. The results indicate that the considered system reduces outage probability and average BER significantly, especially for low channel quality. Finally, the closed-form expressions derived in this work are compared to the results of Monte Carlo simulations, for verification.

• 한국통신학회논문지
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• 제34권1B호
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• pp.16-23
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• 2009

이 논문은 멀티 홉 무선 메쉬 네트워크에서 제공하는 라우팅 프로토콜이 적용된 라우팅 metric에 따라 최적의 경로를 얼마나 잘 찾는가에 관한 논문이다. 최근에 제시된 라우팅 metric은 Link Quality (LQ)를 정확히 나타내도록 설계되어있지만, 많은 metric들은 그것을 기반으로 찾은 경로들이 얼마나 많은 비율로 최적의 경로를 찾을 수 있는지에 대해서 검증하지 않았다. 우리는 최근에 잘 디자인된 라우팅 metric들과 가장 많이 사용되는 라우팅 프로토콜의 다양한 조합을 고려하였다. 그리고 각각의 라우팅에서 찾은 경로의 최적 정도를 살펴보았습니다. 또한 무선 링크의 비대칭성을 반영한 metric을 위해서 단 방향성을 가지는 라우팅 프로토콜을 제안한다. 시뮬레이션을 통해서 만들어진 최적 경로의 비율이 살펴본 모든 라우팅 metric 및 프로토콜 그리고 네트워크 구조에 대해서 네트웍 트래픽 양에 따라 감소하는 현상을 알 수 있다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1997년도 전력전자학술대회 논문집
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• pp.14-20
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• 1997

Due to several advantages of Pulse Width Modulated(PWM) Converter, such as unity power factor with low-harmonics and energy regeneration, PWM converter has been widely used in industrial application. In every application of energy conversion equipment, the design and implementation must be carried out considering performance and cost. High quality with low cost is the best choice for energy conversion equipment. High dc link voltage can reduce inverter and motor side losses and system dimension compare to low dc link voltage. Analog controller can make PWM converter cheaper without considerable degradation of the performance than digital controller. This paper shows the simplified analog controller-for 600V dc link voltage using stationary reference frame control and the simulation results.

• 전기학회논문지P
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• 제59권1호
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• pp.40-46
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• 2010

DC link electrolytic capacitors are widely used in various PWM power converter system, such as adjustable speed driver(ASD) or DC/DC converter. Electrolytic capacitors, which is the most of the time affected by aging effect, plays a very important role for the power electronics system quality and reliability. This objective of this paper is to propose a improvement method to detect the rise of equivalent series resistor(ESR) in order to realize the online failure prediction of electrolytic capacitor for DC link of PWM power converter. The ESR detection scheme is based on the determination of the electrolytic capacitor AC losses calculated from voltage/current measurement using AC coupling. Therefore, the preposed online failure prediction method has the merits of easy ESR computation and circuit simplicity compare with BPF method. Simulation results show the veridity of the proposed on-line ESR estimation method.

• 한국자동차공학회논문집
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• 제22권3호
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• pp.194-202
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• 2014

Steering axis of suspensions is an important factor that affects ride and handling quality in the vehicle chassis development. Macpherson strut and double wishbone's steering axis are defined geometrically, but multi-link suspensions can not be geometrically analyzed. In this case instant axis theory is commonly used to find a steering axis. Since the steering axis is moving with varying caster and kingpin inclination angle, this method approximately corresponds with exact solution. In this paper, we propose a velocity analysis method to find a pure rotational axis of the wheel relative to suspension arms, that is exact solution of the steering axis. This paper extends the method to analyze the steering axis of multi-link suspensions with bushing compliance. The analysis results applied to double wishbone and multi-link suspensions demonstrate validity and accuracy of the proposed method.

• 한국공작기계학회논문집
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• 제10권6호
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• pp.63-70
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• 2001

This study is concerned with Finite Element Analysis on welded part of control link fur automobile. For analysis, control link was modeled into two parts, ring and rod. Heating condition, temperature distributions and fatigue fracture strength were analyzed using "HEAT III" and "NDURE" module of NISA II. Metal flow in the process of welding was simulat- ed by $DEFORM^{TM}2D$.The analyzed results were compared with experimental inspection. Quality of welded part was able to be improved by controlling metal flow in the process of welding by increase the friction constant of ring part. Heat transfer analysis and flow simulations were in good agreement wish welding experiments.