• Journal of Power Electronics
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• 제18권3호
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• pp.863-870
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• 2018

The traditional power control theories for the harmonic reduction methods in multilevel inverters are found to be unreliable under unbalanced load conditions. The unreliability in harmonic mitigation is caused by voltage fluctuations, non-linear loads, the use of power switches, etc. In general, the harmonics are reduced by filters. However, such devices are an expensive way to provide a smooth and fast response to secure power systems during dynamic conditions. Hence, the Decoupled Double Synchronous Reference Frame (DDSRF) theory combined with a State Delay Controller (SDC) is proposed to achieve a harmonic reduction in power systems. The DDSRF produces a sinusoidal harmonic that is the opposite of the load harmonic. Then, it injects this harmonic into power systems, which reduces the effect of harmonics. The SDC is used to reduce the delay between the compensation time for power injection and the generation of a reference signal. The proposed technique has been simulated using MATLAB and its reliability has been verified experimentally under unbalanced conditions.

• 한국소음진동공학회논문집
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• 제15권9호
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• pp.1037-1044
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• 2005

This paper is concerned with the active vibration control of a grid structure equipped with piezoceramic sensors and actuators. The grid structure is a replica of the solar panel commonly mounted on satellites, which contains complex natural mode shapes. The multi-input and multi-output positive position feedback controller is considered as an active vibration controller for the grid structure. A new concept, the block-inverse technique, is proposed to cope with more modes than the number of actuators and sensors. This study also deals with the stability and the spillover effect associated with the application of the multi-input multi-output positive position feedback controller based on the block-inverse technique. It was found that the theories developed in this study are capable of predicting the control system characteristics and its performance. The new multi-input multi-output positive position feedback controller was applied to the test structure using a digital signal processor and its efficacy was verified by experiments.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.203-210
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• 2018

As the modernization of the nuclear instrumentation system progresses, research reactors have adopted digital wide-range neutron power measurement (DWRNPM) systems. These systems typically monitor the neutron flux across a range of over 10 decades. Because neutron detectors only measure the local neutron flux at their position, the local neutron flux must be converted to total reactor power through calibration, which involves mapping the local neutron flux level to a reference reactor power. Conventionally, the neutron power range is divided into smaller subranges because the neutron detector signal characteristics and the reference reactor power estimation methods are different for each subrange. Therefore, many factors should be considered when preparing the calibration procedure for DWRNPM channels. The main purpose of this work is to serve as a reference for performing the calibration of DWRNPM systems in research reactors. This work provides a comprehensive overview of the calibration of DWRNPM channels by describing the configuration of the DWRNPM system and by summarizing the theories of operation and the reference power estimation methods with their associated calibration procedure. The calibration procedure was actually performed during the commissioning of an open-pool type research reactor, and the results and experience are documented herein.

• 한국통신학회논문지
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• 제19권12호
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• pp.2498-2507
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• 1994

본 논문은 코히어런트 복조방식을 사용하는 디지털 위성통신 시스템에서 위성체의 운동으로 인하여 발생된 도플러 주파수를 추적할 수 있는 최적 동기방식의 위상추적장치를 제안하였다. 위성통신 시스템에서 위성체의 운동에 의한 도플러 주파수량과 최적 동기 추적에 의한 시스템 설계 기술을 수식적으로 나타내었다. 이를 바탕으로 하여 디지털 위성통신 시스템에 활용하기 위하여 DSP칩, RAM 및 PROM등에 의한 디지털 처리기술과 80286 프로세서를 이용하여 구현한 도플러 주파수 추적 장치의 설계 기술을 설명하였다. 설계된 도플러 주파수 추적장치는 INTELSAT VA위성을 이용하여 실험한 결과와 수식 계산 결과를 비교함으로써 시스템의 성능을 입증하였다.

• 음성과학
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• 제13권3호
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• pp.49-65
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• 2006

Recently, several theories on the digital speech signal processing expanded the communication boundary between human beings and machines drastically. The aim of this study is to collect dialectal speech in Korea on a large scale and to establish a digital speech data base in order to provide the data base for further research on the Korean dialectal and the creation of value-added network. 528 informants across the country participated in this study. Acoustic characteristics of vowels and consonants are analyzed by Power spectrum and Spectrogram of CSL. Test words were made on the picture cards and letter cards which contained each vowel and each consonant in the initial position of words. Plot formants were depicted on a vowel chart and transitions of diphthongs were compared according to dialectal speech. Spectral times, VOT, VD, and TD were measured on a Spectrogram for stop consonants, and fricative frequency, intensity, and lateral formants (LF1, LF2, LF3) for fricative consonants. Nasal formants (NF1, NF2, NF3) were analyzed for different nasalities of nasal consonants. The acoustic characteristics of dialectal speech showed that young generation speakers did not show distinction between close-mid /e/ and open-mid$/\epsilon/$. The diphthongs /we/ and /wj/ showed simple vowels or diphthongs depending to dialect speech. The sibilant sound /s/ showed the aspiration preceded to fricative noise. Lateral /l/ realized variant /r/ in Kyungsang dialectal speech. The duration of nasal consonants in Chungchong dialectal speech were the longest among the dialects.

• 한국해양공학회지
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• 제34권5호
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• pp.371-376
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• 2020

Underwater acoustics, which is the study of the phenomena related to sound waves in water, has been applied mainly in research on the use of sound navigation and range (SONAR) systems for communication, target detection, investigation of marine resources and environments, and noise measurement and analysis. Underwater acoustics is mainly applied in the field of remote sensing, wherein information on a target object is acquired indirectly from acoustic data. Presently, machine learning, which has recently been applied successfully in a variety of research fields, is being utilized extensively in remote sensing to obtain and extract information. In the earlier parts of this work, we examined the research trends involving the machine learning techniques and theories that are mainly used in underwater acoustics, as well as their applications in active/passive SONAR systems (Yang et al., 2020a; Yang et al., 2020b; Yang et al., 2020c). As a follow-up, this paper reviews machine learning applications for the inversion of ocean parameters such as sound speed profiles and sediment geoacoustic parameters.

• 대한토목학회논문집
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• 제36권5호
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• pp.805-817
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• 2016

본 연구에서는 쓰나미에 대응할 수 있는 다양한 파형의 고립파를 수리/수치파동수조에서 안정적으로 생성시키기 위하여 기존의 고립파 근사이론에 관한 검토를 수행하였다. 그리고 이 근사이론식을 토대로 다양한 고립파의 파형을 추정할 수 있는 두 가지 방법을 제안하였다. 이 방법들은 기존의 고립파 근사식들을 토대로 파형분포조절계수와 가상수심계수를 적용하여 다양한 파형 및 유속을 추정하는 절차를 거친다. 새롭게 제안한 고립파 추정방법들을 수리/수치파동수조의 조파에 적용하였다. 그 결과, 수리파동수조에서는 조파기의 위치정보신호를 추정할 수 있을 뿐만 아니라, 기존의 수리모형실험의 입력신호와 매우 유사한 것을 확인할 수 있었다. 수치파동수조에서는 파랑을 생성하기 위하여 고립파의 파형 및 유속을 적용하였다. 그리고 기존의 고립파 근사이론으로는 재현할 수 없었던 쓰나미의 파형을 조파할 수 있었고, 기존 실험결과와 높은 일치도를 나타내는 것을 확인할 수 있었다. 이로써 수리/수치파동수조에서 안정적인 쓰나미를 생성하기 위하여 제안한 두가지 추정방법의 타당성 및 유효성을 확인할 수 있었다.

• Journal of Positioning, Navigation, and Timing
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• 제7권1호
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• pp.37-42
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• 2018

This paper proposed a microstrip antenna that can perform jamming of satellite signals from the GPS L5, GLONASS G3, BDS B2 frequency bands (1164 - 1217 MHz) that are employed mainly for military purposes among the GNSS frequencies using unmanned aircrafts over the enemy's sky in time of emergency. The single element in the proposed antenna can be easily mounted to unmanned aircrafts. This study analyzed the characteristics of miniaturization and beam of radiating elements by applying the image theories and perturbation effect to satisfy the uniform level at ${\pm}45^{\circ}$ of beam steering goal due to the phase delay after antenna array. The designed microstrip antenna had a miniaturized radiating element area (x-y plane), which was reduced by 76.3% compared to that of basic microstrip antenna, and its beam width was $190^{\circ}$ in the E-plane and $140^{\circ}$ in the H plane. In addition, the simulation was conducted to determine the characteristics due to the phase delay by arranging the designed single microstrip antenna by $1{\times}4$ array and the results showed that beam steering of ${\pm}45^{\circ}$ is possible in the H-plane on the basis of $0^{\circ}$. Thus, the proposed antenna was verified to be effective in satellite signal jamming in the air as it was attached to the lower end of unmanned aircrafts.

• 한국인터넷방송통신학회논문지
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• 제16권3호
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• pp.203-211
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• 2016

유전자 코드는 바이오 정보 처리에 키 포인트로 인체의 유기적인 조직체이다. 현대 과학에서는 유전자 코드 분자구조의 신비스러운 특성을 체계적으로 설명하고 이해하는데 연구가 집중되고 있다. 본 논문에서는 유전자 시스템을 대칭적으로 해석하는데 중점을 두었고, Jacket 행렬로 무잡음 RNA 유전자 코드를 가장 단순하게 해석했다. 이유는 Jacket 행렬과 RNA는 그 역행렬이 Element (Block)-wise Inverse로 그 역(Inverse)도 자신이란 점과 대칭적 성질, 그리고 Kronecker곱을 갖기 때문이다. 제안된 방법이 유전자 RNA 코돈(Codon : 괘(卦))의 견지에서 Jacket 행렬의 분해를 통해 간단하고 명료함을 보인다.

• 대한기계학회논문집A
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• 제38권5호
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• pp.475-482
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• 2014

유압밸브 구동용 서보 액추에이터는 항공기, 자동차의 유압시스템 그리고 산업용 유압시스템의 정밀한 작동에 중요한 장치이다. 서보 액추에이터의 신뢰성 있는 동작은 전체 유압시스템의 정밀한 제어에 큰 영향을 미친다. 서보 액추에이터의 주파수 응답특성, 스텝 응답특성과 같은 응답특성은 액추에이터의 성능을 판단하는 중요한 기준이 된다. 본 논문에서는 신뢰성해석을 통해 신뢰성 있는 동작과 응답특성을 만족시키기 위한 구성 부품에 대한 분석을 실시하였다. 또한 신뢰성 있는 동작과 빠른 응답성을 구현하기 위해 현장의 경험적 지식과 문헌 및 전문가의 전자기 이론을 통해 유압밸브 구동용 서보 액추에이터의 설계 파라미터를 도출하였다. 보빈, 요크, 플런저의 설계값, 그리고 코일의 감긴 수와 같은 서보 액추에이터의 설계값들을 결정하는 설계 파라미터를 제안하고, 설계방정식을 통해 산출한 설계값을 유한요소해석을 통해 타당성을 검증하였다. 또한 서보 액추에이터가 장착된 유압밸브의 성능시험을 통해 제안한 설계 방안의 타당성을 검증하였다.