• Journal of Power Electronics
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• 제19권4호
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• pp.1020-1033
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• 2019

This paper presents a control strategy to enhance the accuracy of reactive power sharing between paralleled three-phase inverters in an islanded microgrid. In this study, the mismatch of power sharing when the line impedances have significant differences between inverters connected to a microgrid has been solved, the accuracy of the reactive power sharing in an islanded microgrid is increased, the voltage droop slope is tuned to compensate for the mismatch of voltage drops across the line impedances by using an enhanced droop controller. The proposed method ensures accurate power sharing even if the microgrid has local loads at the output of the inverters. The control model has been simulated by MATLAB/Simulink with two or three inverters connected in parallel. Simulation results demonstrate the accuracy of the implemented control method. Furthermore, in order to validate the theoretical analysis and simulation results, an experimental setup was built in the laboratory. Results obtained from the experimental setup verify the effectiveness of the proposed method.

• Advances in materials Research
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• 제8권1호
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• pp.1-10
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• 2019

Roll bonding (RB) process of bi-metal laminates as a new noble method of bonding has been widely used in the production of bimetal laminates. In the present study, asymmetric roll bonding process as a new noble method has been presented to produce Al/Cu bimetallic laminates with the thickness reduction ratios 10%, 20% and 30% together with mismatch rolling diameter ($\frac{R_2}{R_1}$) ratio 1:1, 1:1.1 and 1:1.2. ABAQUS as a finite element simulation software was used to model the deformation of samples. The main attention in this study focuses on the bonding properties of Al/Cu samples. The effect of the $\frac{R_2}{R_1}$ ratios was investigated to improve the bond strength. During the simulation, for samples produced with $\frac{R_2}{R_1}=1:1.2$, the vertical plastic strain of samples was reach the maximum value with a high quality bond. Moreover, the peeling surface of samples after the peeling test was investigated by the scanning electron microscopy (SEM).

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권11호
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• pp.5382-5403
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• 2018

In this paper, for a spectrum sensing purpose, we heuristically established a test statistic (TS) from a sample covariance matrix (SCM) for multiple antennas based cognitive radio. The TS is formulated as a scaled-energy which is calculated as a sum of scaled diagonal entries of a SCM; each of the diagonal entries of a SCM scaled by corresponding row's Euclidean norm. On the top of that, by combining theoretical results together with simulation observations, we have approximated a decision threshold of the TS which does not need prior knowledge of noise power and primary user signal. Furthermore, simulation results - which are obtained in a fading environment and in a spatially correlating channel model - show that the proposed method stands effect of noise power mismatch (non-uniform noise power) and has significant performance improvement compared with state-of-the-art test statistics.

• 신재생에너지
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• 제19권3호
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• pp.1-12
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• 2023

This study aims to evaluate the optimal size of the hydrogen facility to be installed in a zero-energy district in terms of load matching and facility efficiency. A mismatch between energy generation and consumption is a common occurrence in zero-energy districts. This mismatch adversely effects the energy grid. However, using an energy carrier such as hydrogen can solve this problem. To determine the optimal size of hydrogen fuel cells to be used on-site, simulation of hydrogen installation is required at both district-and building- levels. Each case had four operating schedules. Therefore, we evaluated eight scenarios in terms of load matching, heat loss, and facility operational efficiency. The results indicate that district-level installation of hydrogen facilities enables more efficient energy use. Additionally, based on the proposed model, we can calculate the optimal size of the hydrogen facility.

• 한국정밀공학회지
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• 제21권8호
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• pp.188-195
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• 2004

In this paper we analyzed the mechanical behavior with respect to the thickness variation of elastic foundation(fatty tissue) in end-to-end anastomosis. This study considered the preliminary deformed shape induced by suturing in the anastomosis of coronary artery and PTFE with different diameters using simplified suturing model and the fatty tissue surrounding heart and coronary artery for more accurate result using finite element method. Area compliance(CA) was used to analyze the final deformed shape of the anastomotic part with respect to the thickness variation of fatty tissue under mean blood pressure, 100mmHg(13.3㎪). And Equivalent and circumferential stresses in the anastomosis were also analyzed with respect to the change of initial diameter ratio( $R_1$) and fatty tissue thickness( $T_{F}$). The results obtained were as follows : 1 When the elastic foundation, assumed to be incompressive material, surrounded the grafts in anastomosis, the compliance mismatch of artery and PTFE was reduced by 47 -72%. 2. As the initial diameter ratio( $R_1$) became larger, the higher difference of compliance was induced in spite of elastic foundation surrounding grafts. 3. The maximum nondimensional circumferential stress is twice or three times as high as the maximum nondimensional equivalent stress in the anastomotic part.t.

• 한국통신학회논문지
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• 제29권2B호
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• pp.228-239
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• 2004

정보보호산업 성장의 가장 큰 애로요인 중 하나로 시장의 미성숙, 정보보호에 대한 인식 부족 등과 함께 전문 인력의 부족 등이 꼽히고 있는 가운데, 정보보호인력은 공급부족으로 인한 수급 불일치 현상을 보이고 있다. 이러한 현상은 산업에 대한 수요는 필연적으로 인력에 대한 수요를 발생시키게 되는데, 정보보호산업이 급속히 성장함에 따라 시기 적절한 정보보호인력의 양성 및 공급 대책을 수립함에 있어 어려움이 있었기 때문인 것으로 파악된다. 본 연구는 정보보호인력의 원활한 공급을 위해서는 정보보호인력의 수급체계에 대한 분석이 선행되어야 한다는데에 초점을 두고, 시스템 다이내믹스 방법론(System Dynamics)을 이용하여 정보보호인력의 수급체계 분석을 위한 모형을 작성하였다. 모형 구현의 궁극적인 목표는 정보보호인력의 수급체계가 갖고 있는 행태를 분석해 보고자하는 것이며, 이 때 주요정책변수를 조절하여 구현한 결과를 통해 정보보호인력의 원활한 공급을 위한 정책마련에 시사점을 주고자 한다.

• 한국통신학회논문지
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• 제29권5C호
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• pp.642-653
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• 2004

정보보호산업 성장의 가장 큰 애로요인 중 하나로 시장의 미성숙, 정보보호에 대한 인식 부족 등과 함께 전문 인력의 부족 등이 꼽히고 있는 가운데, 정보보호인력은 공급부족으로 인한 수급 불일치 현상을 보이고 있다. 이러한 현상은 산업에 대한 수요는 필연적으로 인력에 대한 수요를 발생시키게 되는데, 정보보호산업이 급속히 성장함에 따라 시기 적절한 정보보호인력의 양성 및 공급 대책을 수립함에 있어 어려움이 있었기 때문인 것으로 파악된다. 본 연구는 정보보호인력의 원활한 공급을 위해서는 정보보호인력의 수급체계에 대한 분석이 선행되어야 한다는 데에 초점을 두곤 시스템 다이내믹스 방법론(System Dynamics)을 이용하여 정보보호인력의 수급체계 분석을 위한 모형을 작성하였다. 모형 구현의 궁극적인 목표는 정보보호인력의 수급체계가 갖고 있는 형태를 분석해 보고자 하는 것이며, 이 때 주요정책변수를 조절하여 구현한 결과를 통해 정보보호인력의 원활한 공급을 위한 정책마련에 시사점을 주고자 한다.

• 음성과학
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• 제15권2호
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• pp.67-77
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• 2008

In this paper, we implemented a robust speech recognizer using the TMS320VC33 DSP. For this implementation, we had built speech and noise database suitable for the recognizer using spectral subtraction method for noise removal. The recognizer has an explicit structure in aspect that a speech signal is enhanced through spectral subtraction before endpoints detection and feature extraction. This helps make the operation of the recognizer clear and build HMM models which give minimum model-mismatch. Since the recognizer was developed for the purpose of controlling car facilities and voice dialing, it has two recognition engines, speaker independent one for controlling car facilities and speaker dependent one for voice dialing. We adopted a conventional DTW algorithm for the latter and a continuous HMM for the former. Though various off-line recognition test, we made a selection of optimal conditions of several recognition parameters for a resource-limited embedded recognizer, which led to HMM models of the three mixtures per state. The car noise added speech database is enhanced using spectral subtraction before HMM parameter estimation for reducing model-mismatch caused by nonlinear distortion from spectral subtraction. The hardware module developed includes a microcontroller for host interface which processes the protocol between the DSP and a host.

• 산업경영시스템학회지
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• 제38권1호
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• pp.90-100
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• 2015

This study is conducted to suggest ways to mitigate the mismatch phenomenon between job seekers who want to find right company for themselves and companies looking for appropriate new employees. For this purpose, this study improves the company assessment framework reflecting job seekers interests by using fuzzy analytic hierarchy process. The improved evaluation framework is a three-level hierarchical structure, where there are 4 groups at the top level, 12 factors at the intermediate level and 36 indexes at the bottom level. For the empirical analysis of the applicants preferences based on the improved model, a survey for F-AHP analysis is carried out to university students and then priorities of components in the evaluation model are calculated. Moreover, the differences of priority of the company assessment framework are analyzed for different genders, college years, and major divisions. The results show that job seekers' most concerning factors are wages, stability, working environments, and labor deal, which are ranked highly in this order and the differences in preferences for each type of job seekers (genders, college years, and major divisions) are obvious. The results also show that the male prefers wages to environment, on the other hand female does working environment to wages.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2949-2957
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• 2020

Fatigue crack growth model has been developed for dissimilar metal weld joints of a piping component under cyclic loading, where in the crack is located at the center of the weld in the circumferential direction. The fracture parameter, Stress Intensity Factor (SIF) has been computed by using principle of superposition as K_H + K_M. K_H is evaluated by assuming that, the complete specimen is made of the material containing the notch location. In second stage, the stress field ahead of the crack tip, accounting for the strength mismatch, the applied load and geometry has been characterized to evaluate SIF (K_M). For each incremental crack depth, stress field ahead of the crack tip has been quantified by using J-integral (elastic), mismatch ratio, plastic interaction factor and stress parallel to the crack surface. The associated constants for evaluation of K_M have been computed by using the quantified stress field with respect to the distance from the crack tip. Net SIF (K_H + K_M) computed, has been used for the crack growth analysis and remaining life prediction by Paris crack growth model. To validate the model, SIF and remaining life has been predicted for a pipe made up of (i) SA312 Type 304LN austenitic stainless steel and SA508 Gr. 3 Cl. 1. Low alloy carbon steel (ii) welded SA312 Type 304LN austenitic stainless-steel pipe. From the studies, it is observed that the model could predict the remaining life of DMWJ piping components with a maximum difference of 15% compared to experimental observations.