• 한국통신학회논문지
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• 제16권12호
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• pp.1274-1285
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• 1991

이 논문에서는 극이 하나 있는 저역 여파기를 쓰는 정규화된 LMS 앨고리즘의 통계학적 수렴을 분석하였다. 이 앨고리즘에서 저역 여파기는 출력이 입력 신호전력의 추정 값에 가깝도록 순환적으로 조정하는 데에 쓰인다. 또한 이때 얻은 입력신호 전력 추정값은 수렴 매개변수를 정규화하는데에 쓰인다. 적응여파기 입력값들이 독립이고 평균이 0이며 넓은 뜻에서 정상인 가우시안 확률과정이라는 가정아래에서 여파기 계수의 평균, 제곱 평균과 제곱 평균 추정오차의 성격을 나타내는식을 얻었다. 평균과 제곱 평균수렴에 필요한 조건을 살펴보았으며 정규화된 LMS 앨고리즘의 성능과 LMS 앨고리즘의 성능을 견주어 보았다. 해석적 방법과 경험적 방법이 매우 잘 들어 맞는다는 것을 보여주는 실험결과도 보였다.

• 한국전자파학회논문지
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• 제28권11호
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• pp.924-927
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• 2017

본 논문에서는 6~18 GHz 대역 8-비트 true time delay(TTD) 회로의 설계 및 측정결과에 대하여 기술하였다. 단위 지연 회로는 상대적으로 시간 지연 변화율이 일정한 m-유도 필터(m-derived filter)를 이용하였다. 설계한 8-비트 TTD는 2개의 single-pole double-throw(SPDT)와 7개의 double-pole double-throw(DPDT) 스위치로 구현하였으며, 인덕터를 이용하여 반사 특성을 개선하였다. 설계된 8-비트 TTD는 $0.18{\mu}m$ CMOS 공정을 이용하여 제작하였다. 측정된 TTD 회로의 시간 가변 범위는 250 ps이고, 시간 지연 해상도는 약 1 ps이다. 6~18 GHz의 동작 주파수에서 RMS 시간 지연 오차는 11 ps 미만이며, 입출력 반사 손실은 10 dB 이상이다. 공급 전압은 1.8 V이며, 소비 전력은 0.0 mW이다. 칩 면적은 $2.36{\times}1.04mm^2$이다.

• Journal of Power Electronics
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• 제16권1호
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• pp.297-309
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• 2016

Grid-connected inverters (GCIs) with an LCL output filter have the ability of attenuating high-frequency (HF) switching ripples. However, by using only grid-current control, the system is prone to resonances if it is not properly damped, and the current distortion is amplified significantly under highly distorted grid conditions. This paper proposes a synchronous reference frame equivalent proportional-integral (SRF-EPI) controller in the αβ stationary frame using the parallel virtual resistance-based active damping (PVR-AD) strategy for grid-interfaced distributed generation (DG) systems to suppress LCL resonance. Although both a proportional-resonant (PR) controller in the αβ stationary frame and a PI controller in the dq synchronous frame achieve zero steady-state error, the amplitude- and phase-frequency characteristics differ greatly from each other except for the reference tracking at the fundamental frequency. Therefore, an accurate SRF-EPI controller in the αβ stationary frame is established to achieve precise tracking accuracy. Moreover, the robustness, the harmonic rejection capability, and the influence of the control delay are investigated by the Nyquist stability criterion when the PVR-based AD method is adopted. Furthermore, grid voltage feed-forward and multiple PR controllers are integrated into the current loop to mitigate the current distortion introduced by the grid background distortion. In addition, the parameters design guidelines are presented to show the effectiveness of the proposed strategy. Finally, simulation and experimental results are provided to validate the feasibility of the proposed control approach.

• 한국정보통신학회논문지
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• 제13권10호
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• pp.2197-2204
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• 2009

본 논문에서는 다중입력 다중출력 (Multiple Input Multiple Output: MIMO) 시스템에서 Maximum Likelihood (ML) 수신기와 같은 성능을 가지지만 복잡도가 낮은 Sphere Decoding (SD) 알고리즘에 대해 분석하고 그 성능을 평가한다. 각각의 송신 안테나에서 채널로 전송되는 독립적인 신호는 QPSK 와 16QAM 방식을 사용하여 변조되며, 채널은 산란이 활발하게 일어나는 레일리 (Rayleigh) 평탄 페이딩 채널로 가정한다. 수신기에서 수신된 신호는 Fincke & Pohst SD 알고리즘에 의해 각 송신 안테나로부터의 독립적인 신호로 검파되며, 그 성능이 ZF (Zero Forcing), MMSE (Minimum Mean Square Error), SIC (Successive Interference Cancelation), 그리고 ML 수신기의 성능과 비교되었다. 추가적으로 복잡도를 줄이기 위해 개선된 형태인 Viterbo & Boutros SD 알고리즘을 이용하여 검파된 신호의 BER 성능과 부동 소수점 연산량(Floating Point Operations: FLOPS)이 각각 비교 분석되었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.551-554
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• 2005

The method of the reduction of the automotive induction noise can be classified by the method of passive control and the method of active control. However, the passive control method has a demerit to reduce the effect of noise reduction at low frequency (below 500Hz) range and to be limited by a space of the engine room. Whereas, the active control method can overcome the demerit of passive control method. The algorithm of active control is mostly used the LMS (Least-Mean-Square) algorithm because the LMS algorithm can easily obtain the complex transfer function in real-time. Especially, When the Filtered-X LMS (FXLMS) algorithm is applied to an ANC system. However, the convergence performance of LMS algorithm goes bad when the FXLMS algorithm is applied to an active control of the induction noise under rapidly accelerated driving conditions. Thus Normalized FXLMS algorithm was developed to improve the control performance under the rapid acceleration. The advantage of Normalized FXLMS algorithm is that the step size is no longer constant. Instead, it varies with time. But there is one additional practical difficulty that can arise when a nonstationary input is used. If the input is zero for consecutive samples, then the step size becomes unbounded. So, in order to solve this problem. the Correlation FXLMS algorithm was developed. The Correlation FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. In this paper, the performance of the Correlation FXLMS Is presented in comparison with that of the other FXLMS algorithms based on computer simulations.

• Journal of Power Electronics
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• 제18권6호
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• pp.1791-1804
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• 2018

To achieve a fast dynamic response and to solve the multi-objective control problems of the output currents, capacitor voltages and system constraints, this paper proposes a deadbeat and hierarchical predictive control with space-vector modulation (DB-HPC-SVM) for five-level nested neutral point piloted (NNPP) converters. First, deadbeat control (DBC) is adopted to track the reference currents by calculating the deadbeat reference voltage vector (DB-RVV). After that, all of the candidate switching sequences that synthesize the DB-RVV are obtained by using the fast SVM principle. Furthermore, according to the redundancies of the switch combination and switching sequence, a hierarchical model predictive control (MPC) is presented to select the optimal switch combination (OSC) and optimal switching sequence (OSS). The proposed DB-HPC-SVM maintains the advantages of DBC and SVM, such as fast dynamic response, zero steady-state error and fixed switching frequency, and combines the characteristics of MPC, such as multi-objective control and simple inclusion of constraints. Finally, comparative simulation and experimental results of a five-level NNPP converter verify the correctness of the proposed DB-HPC-SVM.

• 한국정보통신학회논문지
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• 제25권1호
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• pp.102-107
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• 2021

본 논문에서는 입력 포화가 존재하는 다중 에이전트 시스템의 봉쇄제어 문제를 다룬다. 봉쇄제어의 목표는 추종 에이전트들을 리더 에이전트들에 의해 형성된 convex hull 안으로 몰아넣음으로써 군집 행동을 얻는 것이다. 본 논문에서는 일정한 속도로 움직이는 리더 에이전트들을 고려한다. 움직이는 리더들을 고려한 봉쇄 문제를 해결하기 위하여 PI기반의 분산제어 알고리즘을 제안한다. 다음으로 추종 에이전트들의 목표 위치로의 수렴성을 해석한다. 구체적으로 포화 비선형성을 고려하기 위하여 적분 형태의 리아프노프 함수를 적용한다. 그리고 Lasalle's Invariance Principle을 기반으로 임의의 상수 이득들에 대하여 오차 상태들의 점근적 수렴성을 보인다. 마지막으로 고정된 리더들과 일정한 속도로 움직이는 리더들을 고려한 시뮬레이션을 진행하여 이론적 결과를 검증하였다.

• Nuclear Engineering and Technology
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• 제54권1호
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• pp.110-116
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• 2022

Human failure event (HFE) dependency analysis is a part of human reliability analysis (HRA). For efficient HFE dependency analysis, a maximum number of minimal cut sets (MCSs) that have HFE combinations are generated from the fault trees for the probabilistic safety assessment (PSA) of nuclear power plants (NPPs). After collecting potential HFE combinations, dependency levels of subsequent HFEs on the preceding HFEs in each MCS are analyzed and assigned as conditional probabilities. Then, HFE recovery is performed to reflect these conditional probabilities in MCSs by modifying MCSs. Inappropriate HFE dependency analysis and HFE recovery might lead to an inaccurate core damage frequency (CDF). Using the above process, HFE recovery is performed on MCSs that are generated with a non-zero truncation limit, where many MCSs that have HFE combinations are truncated. As a result, the resultant CDF might be underestimated. In this paper, a new method is suggested to incorporate HFE recovery into the MCS generation stage. Compared to the current approach with a separate HFE recovery after MCS generation, this new method can (1) reduce the total time and burden for MCS generation and HFE recovery, (2) prevent the truncation of MCSs that have dependent HFEs, and (3) avoid CDF underestimation. This new method is a simple but very effective means of performing MCS generation and HFE recovery simultaneously and improving CDF accuracy. The effectiveness and strength of the new method are clearly demonstrated and discussed with fault trees and HFE combinations that have joint probabilities.

• Journal of Korea Trade
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• 제27권1호
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• pp.79-100
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• 2023

Purpose - The purpose of this study is to analyze the market power of the Korea Container Shipping Market (Intra Asia, Korea-Europe, and Korea-U.S.) to verify the existence of collusion empirically, and to answer whether the joint actions of liner market participants in Korea have formed market dominance for each route. Precisely, it will be verified through the Lerner index as to whether the regional market of Asia is a monopoly, oligopoly, or perfect competition. Design/methodology - This study used a Lerner index adjusted with elasticity presented in the New Imperial Organization (NEIO) studies. NEIO refers to a series of empirical studies that estimate parameters to judge market power from industrial data. This study uses B-L empirical models by Bresnahan (1982) and Lau (1982). In addition, NEIO research data statistically contain self-regression and stability problems as price and time series data. A dynamic model following Steen and Salvanes' Error Correction Model was used to solve this problem. Findings - The empirical results are as follows. First, λ, representing market power, is nearly zero in all three markets. Second, the Korean shipping market shows low demand elasticity on average. Nevertheless, the markup is low, a characteristic that is difficult to see in other industries. Third, the Korean shipping market generally remains close to perfect competition from 2014 to 2022, but extreme market power appears in a specific period, such as COVID-19. Fourth, there was no market power in the Intra Asia market from 2008 to 2014. Originality/value - Doubts about perfect competition in the liner market continued, but there were few empirical cases. This paper confirmed that the Korea liner market is a perfect competition market. This paper is the first to implement dynamics using ECM and recursive regression to demonstrate market power in the Korean liner market by dividing the shipping market into Deep Sea and Intra Asia separately. It is also the first to prove the most controversial problems in the current shipping industry numerically and academically.

• 분석과학
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• 제22권2호
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• pp.159-165
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• 2009

기능성 염료의 일종인 fluoran계 염료의 열 변색현상으로부터 열역학적인 함수들을 구하였다. 양성자성 용매와 비양성자성 용매에서 온도변화에 따른 UV-Vis 스펙트럼을 측정함으로서 평형상수와 엔탈피 값을 측정하였다. 양성자성 용매에서는 락톤형으로만 존재하나 비양성자성 용매에서는 락톤형과 쯔비터 이온형이 같이 존재함을 확인하였다. 평형 상수를 결정하는 요인은 용매의 극성도가 아니라 수소결합 주게의 성질에 큰 영향을 받음을 확인하였다. 엔탈피 변화량도 측정하였다. 온도 변화에 따라 열 변색 현상이 잘 일어나므로 엔탈피 변화량은 약 -2.0 kJ/mol정도이며, 따라서 열린형이 닫힌형보다도 에너지가 안정함을 확인하였다. 산에 의한 엔탈피 변화량은 양성자성 용매에서는 거의 0 kJ/mol에 가까우며 비양성자성 용매에서는 일정한 경향성을 찾기 어려웠으며. 또한 엔트로피와 깁스 자유에너지도 일정한 경향성을 보이지 않았다. 이러한 열역학적인 분석 결과는 기능성 염료의 디자인이나 합성에서 중요한 정보를 제공할 수 있다.