• Journal of Power Electronics
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• 제16권2호
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• pp.717-730
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• 2016

The harmonic components of grid voltage result in oscillations of the calculated phase obtained via phase synchronization. This affects the security and stability of grid-connected converters. Moving average filter, delayed signal cancellation and their related harmonic elimination algorithms are major methods for such issues. However, all of the existing methods have their limitations in dealing with multiple harmonics issues. Furthermore, few studies have focused on a comparison and evaluation of these algorithms to achieve optimal algorithm selections in specific applications. In this paper, these algorithms are quantitatively analyzed based on the derived mathematical models. Moreover, an enhanced moving average filter and enhanced delayed signal cancellation algorithms, which are applicable for eliminating a group of selective harmonics with only one calculation block, are proposed. On this basis, both a comprehensive comparison and a quantitative evaluation of all of the aforementioned algorithms are made from several aspects, including response speed, required data storage size, sensitivity to sampling frequency, and elimination of random noise and harmonics. With the conclusions derived in this paper, better overall performance in terms of harmonic elimination can be achieved. In addition, experimental results under different conditions demonstrate the validity of this study.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.336-340
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• 2003

The frame synchronization should be acquired before performing other data-aided receiving algorithms, such as data-aided channel equalizing, beam-forming and phase, symbol timing, and frequency synchronizing, since all of them are using preamble or training sequence to estimate the amount of error from the received signal. In this paper, we present a new frame synchronization scheme for underwater ultrasonic image burst transmission system, which computes the correlation between received symbol sequence and one CAZAC sequence, composed of the latter half of the first CAZAC sequence of preamble and the first half of the second CAZAC sequence of preamble and then compares a threshold value. If the correlation value is bigger than the threshold value, the frame detector determines that the frame synchronization is achieved at that sample.

• 한국산학기술학회논문지
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• 제11권9호
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• pp.3428-3434
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• 2010

논문에서는 IS-95 역방향링크 신호의 품질 측정을 위한 알고리즘을 제안하고 구현하였다. 수신 신호의 품질을 측정하기 위해서는 등화, 반송파 주파수 및 위상 오프셋 추정, 타이밍 동기가 반드시 필요하며, 모든 신호처리는 기저대역에서 수행된다. 등화기는 칩간 간섭(InterChip Interference)을 제거하기 위해, 4배 오버샘플링된 샘플에 대해서 동작하도록 설계되었다. 반송파 주파수 및 위상 오프셋 추정은 데이터 및 타이밍 정보 없이도 가능하도록 하였기 때문에, 타이밍 동기 이전에 수행된다. 타이밍 동기 시에 사용되는 보간 수(Interpolation Number)에 따라 측정의 정확도가 증가하지만, 계산량도 증가하게 된다. 따라서, 제안된 알고리즘이 구현될 플랫폼 성능에 따라 보간 수를 적절히 선택해야한다.

• 한국군사과학기술학회지
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• 제14권1호
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• pp.114-122
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• 2011

In this paper, we have identified the system instability factors in a bistatic radar system using pulse chasing and considered their effects on the bistatic receiver's MTI(Moving Target Indication) improvement performance. The pulse chasing is a method to efficiently scan a restricted search area within the limited transmitter power and time in a bistatic radar and to track a series of transmitted pulses using the receiver beam which has ideally matched to the pulse propagation rate. In this paper, we have discussed the interrelationship between the pulse chasing and time and frequency/phase synchronization and described the effects of the identified system instability factors on two kinds of MTI filter configuration, single delay-line and double delay-line, in the bistatic radar. And also, we have confirmed that the overall system improvement is restricted by a lower improvement factor among identified them, and discussed the allowable tolerance of the time and frequency/phase synchronization in the bistatic system.

• 한국전자파학회논문지
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• 제26권9호
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• pp.790-797
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• 2015

본 논문에서는 마이크로파용 소프트웨어 기반 폴라 송신기를 구현하고, 경로 간의 동기화를 분석하였다. 폴라 송신기의 위상신호와 진폭신호의 두 경로 간 시간 지연부정합 문제를 해결하기 위해 단순화된 보정알고리즘을 적용하였으며, 보정 전과 보정 후의 두 경로 간 동기화 결과를 비교하였다. 동기화 보정하기 전, 9.3 GHz에서 두 경로 간 지연부정합은 최대 97 nsec가 발생하였으며, 이에 따른 점유대역폭은 12 MHz이었으며, 제안한 보정알고리즘을 적용한 결과, 두 경로 간 동기화를 이루었고, 점유대역폭도 기존의 3.7 MHz로 복원할 수 있음을 확인하였다.

• 한국통신학회논문지
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• 제31권11A호
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• pp.1068-1075
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• 2006

OFDMA방식의 무선 다중 접속 시스템의 상향링크에서 기지국으로부터 서로 다른 거리에 있는 각각의 단말들의 시간동기를 위한 적응적 레인징 기법을 제안한다. 제안 기법은 Timing Phase Compensated Frequency Domain Cross-correlation(TPCFDC)와 Frequency Domain Differential Cross-correlation(FDDC)를 동시에 사용함으로써 TPCFDC의 단점인 Round Trip Delay(RTD)의 범위에 따라 증가되는 상관기의 개수를 줄이고 FDDC를 이용하여 반복적인 레인징을 시도함으로써 초기 레인징을 위한 하드웨어 복잡도를 크게 줄일 수 있다. 제안 기법의 성능을 레인징 성공확률과 시도회수 측면에서 모의실험 하였으며 복잡도가 기존에 비해 10배 가량 감소하더라도 기존 방식과 유사한 레인징 성공 확률을 보임을 확인하였다.

• 한국항행학회논문지
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• 제8권2호
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• pp.163-168
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• 2004

본 논문에서는 HDR-WPAN(high data rate wireless personal area network) 시스템의 CAZAC sequence 특성을 이용한 주파수 동기 알고리즘을 제안하고, 신호 성상도 및 EVM(error vector magnitude)를 통해 성능을 분석해 본다. 제안된 방식에서 주파수 옵셋은 자기상관성이 우수한 12개의 CAZAC sequence 가운데 두 개 sequence의 각 샘플간 위상오차를 추정하였으며, 추정된 위상오차는 다음 sequence 내 각각의 샘플에 곱해지면서 위상오차를 보상하게 된다. 두 개의 sequence로 주파수 옵셋을 보상한 후 남은 잔류 주파수 옵셋은 샘플 당 최대 0.002도 이내가 되며 DQPSK의 경우 20[dB]에서 EVM의 허용 기준값을 만족할 수 있음을 컴퓨터 시뮬레이션을 통해 확인한다.

• 대한전기학회논문지
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• 제36권2호
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• pp.107-113
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• 1987

A complete design of a new digital control circuit for a three-phase controlled rectifier is presented. The circuit consists of a gating signal generating ROM, down counter and adder. Proposed scheme is simple and quite adequate to the microprocessor-based digitally controlled systems. The basic principle and operation characteristics of the circuit are described and experimental-results show good dynamic performance. Synchronization problem with noisy reference is also discussed. The basic phylosophy developed can be extended to the other phase control system, e.g., cycloconverters, ac voltoge controllers, etc.

• 대한의용생체공학회:의공학회지
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• 제39권2호
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• pp.94-102
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• 2018

It is known that gamma-band activity (GBA) and phase synchrony (GBPS) are induced by emotional visual stimuli. However, the characteristics of GBA and GBPS according to different emotional states have not been identified. The purpose of this study is to investigate the changes in gamma-band neuronal synchronization induced by positive and negative emotional visual stimuli using electroencephalograms (EEGs). Thirteen healthy male subjects have participated in the experiment. The induced spectral power in gamma-band was the highest for negative stimuli, and the lowest for neutral stimuli in 300-2,000 ms after the stimulus onset. The inter-regional phase synchronization in gamma-band was increased in 500-2,000 ms, mainly between the bilateral frontal regions and the parieto-occipital regions. Larger number of significant connections were found by negative stimuli compared to positive ones. Judging from temporal and spatial characteristics of the gamma-band activity and phase synchrony increases, the results may imply that affective visual stimuli cause stronger memory encoding than non-emotional stimuli, and this effect is more significant for negative emotional stimuli than positive ones.

• 전기학회논문지
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• 제62권2호
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• pp.201-207
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• 2013

This paper propose seamless transfer operation between grid-connected and stand-alone mode in the three-phase inverter for microgrid. The inverter operates grid-connected mode and stand-alone mode. Grid-connected mode is the inverter connected to grid and stand-alone mode is to deliver energy to the load from inverter at grid fault. When conversion from gird-connected to stand-alone mode, the inverter changes current control to voltage control. When grid restored, the inverter system is conversion from stand-alone to grid-connected mode. In this case, load phase and grid phase are different. Therefore, synchronization is essential. Thus Seamless transfer operation stand-alone to grid-connected mode. In this paper, propose sealmless transfer operation between grid-connceted and stand-alome mode, and this method is verified through simulation and experiment.