• 비파괴검사학회지
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• 제36권2호
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• pp.112-120
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• 2016

The nonlinearity parameter is frequently measured as a sensitive indicator in damaged material characterization or tissue harmonic imaging. Several previous studies have employed the plane wave solution, and ignored the effects of beam diffraction when measuring the non-linearity parameter ${\beta}$. This paper presents a multi-Gaussian beam approach to explicitly derive diffraction corrections for fundamental and second harmonics under quasilinear and paraxial approximation. Their effects on the nonlinearity parameter estimation demonstrate complicated dependence of ${\beta}$ on the transmitter-receiver geometries, frequency, and propagation distance. The diffraction effects on the non-linearity parameter estimation are important even in the nearfield region. Experiments are performed to show that improved ${\beta}$ values can be obtained by considering the diffraction effects.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권2호
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• pp.68-79
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• 2003

We estimated harmonics on power system of AC railway based on quantitatively measured harmonics and investigated the need of facilities for harmonics reduction. In order to analysis harmonics which inflow into power system due to increase in collector voltages and harmonic currents generated from the train when the railway is in operation, the railway system Is sectioned into power supply, railway line, AT, sectioning Post and subsectioning post. For analysis of extension of currents resulting from the railway loads, PWM converter, VVVF inverter and the feeder system are modeled based on the dynamic node technique(DNT). In order to test the usefulness of the DNT for analysis of harmonic effects, the measured harmonic currents and harmonic magnification ratios at the S/K substation are compared with simulation results using DNT modelling, which include the results for two cases with and without filters for suppression of harmonic currents. When 8 cars(4M4T) are in operation, the total sum of harmonic currents resulting from the train at M and T phases, which inflow into the substation along with the railway line, is calculated. Using the harmonics analysis program for railway feeder system with these data, the total harmonic distortion factor(710) at the outgoing point of KEPCO substation is computed. The calculation shows that when the maximum THD at the receiving point of H/K substation was 0.0443% which is much lower than 1.5% which is the allowable value of KEPCO at 154kV as well as IEEE-519 above 132kV This result indicates that any measure for harmonics reduction in Incheon International Airport Railway is not needed.

• 전기학회논문지P
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• 제59권2호
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• pp.185-190
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• 2010

This paper presents the estimation on switching technique via output power source analysis of power conversion unit in electric railway vehicle. The focus of this study suggested an alternative on critical problems by using head electric power(HEP). To achieve this, we have measured output power of HEP, and measurement devices set up at output of transformer connected HEP to analysis quality on output power source of head electric power(HEP) unit in electric railway vehicle. Using results of measurement of it, parameters are assumed for simulation to confirm estimation on switching technique. It is confirmed that switching technique is Selected Harmonic Elimination PWM(SHEPWM) and inverter switching frequency is less than 500[Hz]. Throughout experiment and simulation, it is estimated that switching technique used HEP is advanced SHEPWM and switching frequency is about 300[Hz]. Also leakage inductance in transformer is about $180[{\mu}H]$ less than $365[{\mu}H]$ known.

• 한국정보전자통신기술학회논문지
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• 제14권4호
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• pp.247-256
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• 2021

본 논문에서는 피치 하모닉 움직임 예측과 적응적 신호 크기 예측을 이용한 패킷 손실 알고리즘을 제안한다. 스펙트럼 움직임 예측 방법은 사용 가능한 이전 패킷의 스펙트럼 상의 움직임을 일정한 부대역으로 나누어 손실된 신호의 움직임을 예측하여 복원한다. 제안하는 알고리즘에서는 음성신호를 유성음과 무성음으로 구분하여 유성음의 경우 피치 주파수를 활용하여 피치 하모닉으로 나누어 손실된 신호의 피치 하모닉 움직임을 예측하여 복원하고 무성음의 경우 스펙트럼 움직임 예측 방법을 사용하여 신호를 복원한다. 음성 프레임의 연속 손실이 발생한 경우 LMS(Least Mean Square) 예측기를 사용하여 이전 프레임의 이득 정보를 활용하여 신호 크기를 예측하여 출력 신호의 이득을 조절하는 방법을 제안한다. 객관적 평가방법인 PESQ (Perceptual Evaluation of Speech Quality) 시험을 통해 제안된 알고리즘의 성능을 평가하였고 기존의 방법보다 MOS 0.1의 성능 개선을 보였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.2077-2078
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• 2011

Now a days, the induction motor is widely used in industry automation. Without monitoring the motor fault, maintenance cost is increased undesirably high. The slip frequency is included in the feature frequency, so rotating rotor speed is needed. In this paper, a sensorless motor speed estimation method, rotor slot harmonic(RSH) method is suggested and a solution of rotor bar diagnosis is proposed for motor running with light-load. When the rotor is rotating, it shows the harmonic signal of back-emf voltage related with number of rotor slot. So from the power spectrum of current signal, we can find the rotor speed.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 신호처리소사이어티 추계학술대회 논문집
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• pp.57-60
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• 2003

In this paper, we propose a new excitation enhancement technique to improve the speech quality of low bit rate speech coders. The proposed technique is based on a harmonic model and it is employed only in the decoding process of speech coders without any additional bits. We develop the procedure of harmonic model parameters estimation and harmonic generation. and apply the technique to a current state of the art low bit rate speech coder, ITU-T G.729 Annex D. Also its performance is measured by using the ITU-T P.862 PESQ score and compared to those of the phase dispersion filter and the long-term postfilter applied to the decoded excitation. It is shown that the proposed excitation enhancement technique can improve the quality of decoded speech and provide better quality for male speech than other techniques.

• 대한전기학회논문지:전력기술부문A
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• 제48권5호
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• pp.487-493
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• 1999

To predict the background level of harmonics produced by household appliances, information on the site, capacity, and usage pattern of these loads arenecessary. However, as household appliances are distributed widely and various in type, it is difficult to know these kinds of information accurately. This paper presents a method for estimation of background level of harmonics produced by distributed harmonic sources with readily available data. Large industrial customers are excluded from this study. In this paper, customers are grouped into three classes, i.e. residential, commercial, and industrial. Typical customers for each class are assumed and characteristics of their equipments are modeled. As the proposed method does not require harmonic measurement, it can be employed to forecast voltage total harmonic distribution (VTHD) in the future. An illustrative example is described.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 B
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• pp.1085-1087
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• 2004

The space harmonic analysis, as an analytical method, is used to estimate the flux distribution in the air gap of the brushless motors in this paper. With the flux distribution, back-emf and torque characteristics can be estimated.[1-7] Therefore, the air gap flux distribution of surface type permanent magnet motor according to the motor specifications are studied to estimate the torque characteristics in this paper. To validate the analysis result of this method, 2-dimensional finite element analysis is performed and the air gap flux density is compared to that from space harmonic analysis.

• Current Optics and Photonics
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• 제2권6호
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• pp.606-611
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• 2018

Measurement of the nonlinear optical coefficients is not an easy task since it requires complicated experimental setup and analysis. We suggest an easy way to estimate the relative nonlinear optical tensor components by direct measurement of the output powers of the second harmonic generation and spontaneous parametric down conversion experiments. The experiments were done in quasi-phase-matched type-0 as well as type-1 interactions at similar pump wavelengths in a 5% MgO-doped periodically poled $LiNbO_3$ crystal to obtain the ratio of the nonlinear optical tensor components $d_{33}/d_{31}$ in each experiment. The obtained ratios were then compared with the previously ascertained values [J. Opt. Soc. Am. B, 14, 2268-2294 (1997)].

• Journal of Power Electronics
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• 제14권6호
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• pp.1303-1313
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• 2014

Dynamic behavior of the harmonic detection part of an active power filter (APF) has an essential role in filter compensation performances during transient conditions. Instantaneous power (p-q) theory is extensively used to design harmonic detectors for active filters. Large overshoot of p-q theory method deteriorates filter response at a large and rapid load change. In this study the harmonic estimation of an APF during transient conditions for balanced three-phase nonlinear loads is conducted. A novel fuzzy instantaneous power (FIP) theory is proposed to improve conventional p-q theory dynamic performances during transient conditions to adapt automatically to any random and rapid nonlinear load change. Adding fuzzy rules in p-q theory improves the decomposition of the alternating current components of active and reactive power signals and develops correct reference during rapid and random current variation. Modifying p-q theory internal high-pass filter performance using fuzzy rules without any drawback is a prospect. In the simulated system using MATLAB/SIMULINK, the shunt active filter is connected to a rapidly time-varying nonlinear load. The harmonic detection parts of the shunt active filter are developed for FIP theory-based and p-q theory-based algorithms. The harmonic detector hardware is also developed using the TMS320F28335 digital signal processor and connected to a laboratory nonlinear load. The software is developed for FIP theory-based and p-q theory-based algorithms. The simulation and experimental tests results verify the ability of the new technique in harmonic detection of rapid changing nonlinear loads.