• Journal of Power Electronics
• /
• 제13권5호
• /
• pp.896-908
• /
• 2013

Under high grid impedance conditions, it is difficult to guarantee the stability of grid-connected inverters with an LCL filter designed based on ideal grid conditions. In this paper, the theoretical basis for output impedance calculation is introduced. Based on the small-signal model, the d-d channel closed-loop output impedance models adopting the converter-side current control method and the grid-side current control method are derived, respectively. Specifically, this paper shows how to simplify the stability analysis which is usually complemented based on the generalized Nyquist stability criterion (GNC). The stability of each current-controlled grid-connected system is analyzed via the proposed simplified method. Moreover, the influence of the LCL parameters on the stability margin of grid-connected inverter controlled with converter-side current is studied. It is shown that the stability of grid-connected systems is fully determined by the d-d channel output admittance of the grid-connected inverter and the inductive component of the grid impedance. Experimental results validate the proposed theoretical stability analysis.

• Journal of Plant Biology
• /
• 제27권1호
• /
• pp.33-41
• /
• 1984

The relationships and character variations on 5 taxa of Calystegia were examined by sluster analysis and principal component analysis. Thirteen Calystegia population samples from the middle part of Korea were observed. Although minor differences were noted, essentially similar results were obtained from the phenograms by UPGMA, UPGMC and Ward's clustering methods, and these results were in accordance with those obtained from the ordination plots by principal component analysis. C. soldanella is distantly connected with the other taxa mainly because of its morphologically different leaf organs. Based on the difference on the first principal component, C. hederacae is kept apart from the rest 3 taxa. In the relationships among C. japonica, C. sepium var. americana and C. davurica, mivor differences were obtained from the 3 clustering methods. As to the character variations among different populations within a taxon, they are slight in C. soldanella and C. sepium var. americana, but remarkable in C. hederacae and C. davurica.

• 대한음성학회지:말소리
• /
• 제53호
• /
• pp.93-102
• /
• 2005

The performance of a speech recognition system is generally degraded in telephone environment because of distortions caused by background noise and various channel characteristics. In this paper, data-driven temporal filters are investigated to improve the performance of a specific recognition task such as telephone speech. Three different temporal filtering methods are presented with recognition results for Korean connected-digit telephone speech. Filter coefficients are derived from the cepstral domain feature vectors using the principal component analysis. According to experimental results, the proposed temporal filtering method has shown slightly better performance than the previous ones.

• Food Science and Biotechnology
• /
• 제14권4호
• /
• pp.554-557
• /
• 2005

As a device for taste sensation, an 8-channel taste evaluation system was prepared and applied for discriminant analysis of marketed liquor. The biomimetic polymer membranes for the system were prepared through a casting procedure by employing polyvinyl chloride, bis (2-ethylhexyl)sebacate as plasticizer and electroactive materials such as valinomycin in the ratio of 33:66:1, and were separately attached over the sensitive area of ion-selective electrodes to construct the corresponding taste sensor array. The sensor array in conjunction with a double junction reference electrode was connected to a high-input impedance amplifier and the amplified sensor signals were interfaced to a personal computer via an A/D converter. When the signal data from the sensor array for 3 groups of marketed liquor like Maesilju, Soju and beer were analyzed by principal component analysis after normalization, it was observed that the 1st, 2nd and 3rd principal component were responsible for most of the total data variance, and the analyzed liquor samples were discriminated well in 2 dimensional principal component planes composed of the 1st-2nd and the 1st-3rd principal component.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2011년도 추계학술대회
• /
• pp.907-910
• /
• 2011

제철소에서 생산된 철판의 물류 자동화 시스템을 구축하는데 있어 각 철판에 기록된 정보를 정확하게 파악하여 효과적인 적재 및 운반 시스템을 갖추는 것이 관건이다. 이를 위하여 본 논문에서는 생산 및 운반 정보가 기록된 철판 영상을 분석하여 자동화 시스템을 구축하기 위한 문자 추출 기법을 제안한다. 철판 영상은 가로 방향으로 철판의 정보를 나타내는 문자열을 포함하고 있고, 이러한 문자열이 세로 방향으로 배치되어 있기 때문에 각 문자를 분리하기 위해서는 2차원 기법을 적용하도록 한다. 영상을 획득하는 환경에 따라 문자 분리 성능에 미치는 영향을 최소화하기 위하여 국부 특징을 반영한 효율적인 이진화 기법을 제안하고, 잡음 등에 민감한 특성을 제거하기 위하여 CCA(Connected Component Analysis)를 이용한 문자 여부를 판단하는 방법을 제안한다. 이렇게 분석된 영상에 대해 2차원 투영 기법을 적용하여 철판에 기록된 각 문자를 정확하게 분리하도록 한다. 제안된 문자 추출 기법은 높은 성능을 나타내면서도 저 복잡도를 가지도록 설계하여 제한된 자원을 이용하는 기기에 효과적으로 응용될 수 있다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2008년도 제39회 하계학술대회
• /
• pp.924-925
• /
• 2008

There are many types of grid-connected inverter controllers, PI controller based is the most popular methods. But, a common PI control is produced zero-steady state error and phase delay in sinusoidal reference. Synchronous reference frame or DQ transform based controller is capable for reducing both of zero-steady state error and phase delay is. But DQ transform based controller has cross-coupling component which difficult to analyze the system in single phase model. In this paper, to obtained single phase model of the system, DQ transform based controller is analyzed in two techniques. The first is by neglecting cross-coupling. The second is eliminated cross-coupling component by decoupling method. By these two techniques, single phase model is obtained. Then, the single phase model is analyzed to evaluate its performance in stability and frequency response, through Root Locus and Bode diagram, respectively. MATLAB and PSIM simulation is used to verify the analysis. Simulation result is shown; cross-coupling component has no significant influent to the controller.

• Journal of Power Electronics
• /
• 제17권4호
• /
• pp.1004-1013
• /
• 2017

This paper presents an interleaving scheme for parallel-connected power systems to reduce the DC-link current ripple. A paralleled generator system generates current ripple by the Pulse Width Modulation (PWM) of each generator side converter. The current ripple in the DC-link degrades the efficiency of the whole generator system and decreases the lifetime of the DC-link capacitors. To mitigate these issues, the expression of the DC-link current is derived by a double-integral Fourier analysis while considering the modulation schemes. Optimized interleaving angles for the parallel generator system are obtained based on an analysis to minimize the dominant current harmonics component. Finally, the proposed interleaving scheme reduces the RMS value of the DC-link current ripple. Simulation and experimental results verify the effectiveness of the proposed interleaving scheme.

• Structural Engineering and Mechanics
• /
• 제54권2호
• /
• pp.379-392
• /
• 2015

A number of acceleration-based damage detection methods have been developed but they have not been widely applied in engineering practices because the acceleration response is insensitive to minor damage of civil structures. In this article, a damage detection approach using the long-gauge strain sensing technology and the principle component analysis technology is proposed. The Long gauge FBG sensor has its special merit for damage detection by measuring the averaged strain over a long-gauge length, and it can be connected each other to make a distributed sensor network for monitoring the large-scale civil infrastructure. A new damage index is defined by performing the principle component analyses of the long-gauge strains measured from the intact and damaged structures respectively. Advantages of the long gauge sensing and the principle component analysis technologies guarantee the effectiveness for structural damage localization. Examples of a simple supported beam and a steel stringer bridge have been investigated to illustrate the successful applications of the proposed method for structural damage detection.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2004년도 학술대회지
• /
• pp.764-767
• /
• 2004

The performance of a speech recognition system is generally degraded in telephone environment because of distortions caused by background noise and various channel characteristics. In this paper, data-driven temporal filters are investigated to improve the performance of a specific recognition task such as telephone speech. Three different temporal filtering methods are presented with recognition results for Korean connected-digit telephone speech. Filter coefficients are derived from the cepstral domain feature vectors using the principal component analysis.

• KIEE International Transactions on Power Engineering
• /
• 제2A권4호
• /
• pp.136-144
• /
• 2002

Load models are very important for improving the accuracy of stability analysis and load flow studies. Various loads are connected to a power bus and their characteristics of power consumption change with voltage and frequency. Thus, the effect of voltage/frequency changes must be considered in load modeling. In this work, artificial neural networks-ANNs- were used to construct the component load models for more accurate modeling. A typical residential load was selected and subjected to a test under variable voltage/frequency conditions. Acquired data were used to construct component models by ANNs. The aggregation process of separately determined load models is also presented in the paper. Furthermore, this paper proposes a method to transform a single load model constructed by the aggregation method into a mathematical load model that can be used in traditional power system analysis software.