• Journal of Power Electronics
• /
• 제18권5호
• /
• pp.1357-1368
• /
• 2018

In this paper, a novel high gain bidirectional modular dc-dc converter (BMC) with unipolar and bipolar structures for dc network interconnections is proposed. When compared with traditional dc grid-connecting converters, the proposed converter can achieve a high voltage gain with a simple modular transformerless structure. A sub-modular structure for the BMC is proposed to eliminate the unbalanced current stress between the different power units (levels) in the BMC. This can realize current sharing and standardized production and assembling. In addition, phase-interval operation is introduced to the sub-modules to realize low voltage and current ripple in both sides of the converter. Furthermore, two types of bipolar topologies of the sub-modular BMC were proposed to extend its application in bipolar dc network connections. In addition, the control system was optimized for grid-connection applications by providing various control strategies. Finally, simulations of a 3-level unipolar sub-modular BMC and a 4-level bipolar sub-modular BMC were conducted, and a 1-kW experimental 3-level unipolar prototype was developed to verify the effectiveness of the proposed converter.

• Journal of Electrical Engineering and Technology
• /
• 제12권5호
• /
• pp.1709-1718
• /
• 2017

This paper presents a hybrid stochastic deterministic multi-timescale scheduling (SDMS) approach for generation scheduling of a power grid. SDMS considers flexible resource options including conventional generation flexibility in a chance-constrained day-ahead scheduling optimization (DASO). The prime objective of the DASO is the minimization of the daily production cost in power systems with high penetration scenarios of variable generation. Furthermore, energy storage is scheduled in an hourly-ahead deterministic real-time scheduling optimization (RTSO). DASO simulation results are used as the base starting-point values in the hour-ahead online rolling RTSO with a 15-minute time interval. RTSO considers energy storage as another source of grid flexibility, to balance out the deviation between predicted and actual net load demand values. Numerical simulations, on the IEEE RTS test system with high wind penetration levels, indicate the effectiveness of the proposed SDMS framework for managing the grid flexibility to meet the net load demand, in both day-ahead and real-time timescales. Results also highlight the adequacy of the framework to adjust the scheduling, in real-time, to cope with large prediction errors of wind forecasting.

• 한국의학물리학회:학술대회논문집
• /
• 한국의학물리학회 2002년도 Proceedings
• /
• pp.393-395
• /
• 2002

We propose a method which can replace the DR when measuring performance evaluation parameters of antiscatter grids for DR. We used conventional x-ray films to produce grid images, which were scanned by a film digitizer. The digitizer could provide sampling interval of 87 micrometers and pixel depth of 12 bits. Grid line frequencies were measured using aliasing effect and non-uniformities of grids were measured by transforming scanned pixel values of film images into optical densities.

• Current Optics and Photonics
• /
• 제5권4호
• /
• pp.409-420
• /
• 2021

We propose a method to synthesize a color non-hogel-based computer-generated-hologram (CGH) from light field data of a three-dimensional scene with a hologram pixel pitch shared for all color channels. The non-hogel-based CGH technique generates a continuous wavefront with arbitrary carrier wave from given light field data by interpreting the ray angle in the light field to the spatial frequency of the plane wavefront. The relation between ray angle and spatial frequency is, however, dependent on the wavelength, which leads to different spatial frequency sampling grid in the light field data, resulting in color aberrations in the hologram reconstruction. The proposed method sets a hologram pixel pitch common to all color channels such that the smallest blue diffraction angle covers the field of view of the light field. Then a spatial frequency sampling grid common to all color channels is established by interpolating the light field with the spatial frequency range of the blue wavelength and the sampling interval of the red wavelength. The common hologram pixel pitch and light field spatial frequency sampling grid ensure the synthesis of a color hologram without any color aberrations in the hologram reconstructions, or any loss of information contained in the light field. The proposed method is successfully verified using color light field data of various test or natural 3D scenes.

• 한국측량학회지
• /
• 제20권3호
• /
• pp.265-272
• /
• 2002

지금까지 토공량계산을 위한 많은 방법들이 단순식에서부터 복잡한 방법으로 개발되어 왔다. 일찍이 토공량계산을 위한 기본적인 방법은 상부면적을 x, y방향으로 뻗은 경계선의 사각격자로 나누어 계산한다. 그러나 이들 방법은 많은 측량현장에서 요구되는 토공량견적을 정확하게 계산할 수 없다. 1998년 Easa는 x, y 각 방향으로 같은 선상을 따라 사각격자를 나누었다. 이 방법은 격자 양방향으로 3차의 Hermite 다항식을 이용하였다. 이것은 반드시 동일한 x, y방향의 경계를 따라 표고데이터가 존재해야 하므로 지형의 최대, 최소점 같은 점의 선택을 불가능하게 한다. 이 연구에서 제시된 토공량 계산법은 Easa(1998)방법의 단점을 피하고 장점을 결합시켰다. 제안된 방법은 가로x, 세로y 방향의 각 경계를 따라 3차의 Hermite 다항식을 이용하지만 각각의 부등간격의 격자는 양방향으로 일정하지 않고 부분적으로 비격자형태로 이루어져 있다. 새롭게 제시된 방법은 다른 재래식 방법보다 더 나은 정확도를 제공한다.

• 정보처리학회논문지D
• /
• 제11D권5호
• /
• pp.1011-1020
• /
• 2004

대규모의 데이터를 다루는 여러 시스템에서 데이터를 다수의 병렬 디스크에 분산시켜 저장한 후 질의 처리시 동시에 여러 개의 디스크를 접근함으로써 입출력 성능의 향상을 위한 많은 노력들이 행해져 왔다. 대부분 이전 연구들은 데이터 공간을 이루는 각 차원이 겹치지 않는 여러개의 구간으로 나누어져 전체 데이터 공간이 그리드 형태로 분할되어 있다는 가정하에 각 차원의 구간 번호로 결정되는 그리드 셀에 대해서 효과적으로 디스크 번호를 할당하는 알고리즘 개발에 집중되었다. 하지만, 그들은 데이터 공간을 그리드 형태로 분할하는 방법이 전체 디클러스터링 알고리즘 성능에 미치는 영향을 간과하였다. 본 논문에서 우리는 효과적인 그리드 분할을 통하여 매핑 함수를 이용하는 디클러스터링 알고리즘의 성능을 향상 시켰다. 이를 위하여 영역 질의 크기가 주어졌을 때 겹치는 그리드 셀의 수를 예측하는 모델을 제시하였으며 이를 이용하여 가능한 그리드 분할 방법들 중에서 질의 크기를 감소시키는 분할 방법을 선택하였다. 일반적으로, 다차원 데이터에 대해서는 이진 분할을 하지만 본 논문에서는 더 작은 수의 차원을 선택해서 여러 번 분할함으로써 질의를 만족하는 그리드 셀의 수를 감소시켰다. 다양한 실험 결과에 의하면 본 논문에서 제시한 예측 모델은 질의 크기와 차원에 관계없이 0.5% 이내의 에러율을 보이는 것으로 나타났다. 또한 효과적인 그리드 분할을 통하여 다차원 데이터에 대해서 가장 성능이 좋은 것으로 소개되고 있는 Kronecker sequence 매핑 함수를 이용하는 디클러스터링 알고리즘의 성능을 최대 23배까지 향상시킬 수 있음을 알 수 있었다.

• Journal of Electrical Engineering and Technology
• /
• 제13권1호
• /
• pp.38-50
• /
• 2018

Spatio-temporal load forecasting (STLF) is a foundation for building the prediction-based power map, which could be a useful tool for the visualization and tendency assessment of urban energy application. Constructing one point-forecasting model for each electricity cell in the geographic space is possible; however, it is unadvisable and insufficient, considering the aggregation features of electricity cells and uncertainties in input variables. This paper presents a new STLF method, with a data-driven framework consisting of 3 subroutines: multi-level clustering of cells considering their aggregation features, load regression for each category of cells based on SLS-SVRNs (sparse least squares support vector regression networks), and interval forecasting of spatio-temporal load with sampled blind number. Take some area in Pudong, Shanghai as the region of study. Results of multi-level clustering show that electricity cells in the same category are clustered in geographic space to some extent, which reveals the spatial aggregation feature of cells. For cellular load regression, a comparison has been made with 3 other forecasting methods, indicating the higher accuracy of the proposed method in point-forecasting of spatio-temporal load. Furthermore, results of interval load forecasting demonstrate that the proposed prediction-interval construction method can effectively convey the uncertainties in input variables.

• 한국조경학회지
• /
• 제28권3호
• /
• pp.97-104
• /
• 2000

Studies on the principle of traditional moulding techniques of architecture or structure are very important in the point of the work could accomplish succession to modern design. As an attempt of these work, this study tried to examine traditional moulding techniques applied in planes of ancient architecture and structure closely. The major findings of this study are summarized as follows; It was verified that planes of ancient Korean architectures and structures analyzed in this study was moulded by its multiple partitions with the six or eight partitions of circumference as the fundamental form. The well unearthed in kyong-bok palace recently was moulded by a concentric circle assumed form of 4 circle which was extended with equal interval and divided into multiple of 8 partition of circumference. Chon-duk-jung in chang-duk palace also was moulded by a concentric circle assumed form of 3 circle extended with equal interval, but circle were divide by 6 partitions. It was also found that 6$^{\circ}$§8 partitions of circumference(or its multiple partition) was applied to not only above structures but also the moulding planes of ancient architecture, and as a results, figures revealed in architectures analyzed is classified into three classes. And, this study analyzed arrangements of two temples. As a results, it is discovered that the Grid used in moulding planes of each building fixed the arrangement of buildings. Therefore, moulding by equal partition of circumference decided the form of each building and the relation of element at the same time.

• 대한수학회지
• /
• 제33권2호
• /
• pp.249-258
• /
• 1996

Analysis by the method of characteristics shows that if f and $u_0$ are smooth and $u_0$ has compact support, then the Hamilton-Jacobi equation $$ (H-J) ^{u_t + f(u_x) = 0, x \in R, t > 0, } _{u(x, 0) = u_0(x), x \in R, } $$ has a unique $C^1$ solution u on some maximal time interval $0 \leq t < T$ for which $lim_{t \to T}u(x, t) exists uniformly; but this limiting function is not continuously differentiable.

• 한국정보과학회:학술대회논문집
• /
• 한국정보과학회 2003년도 가을 학술발표논문집 Vol.30 No.2 (3)
• /
• pp.142-144
• /
• 2003

그리드 환경은 수많은 컴퓨팅 자원을 활용하는 시스템으로 자원에 대한 정보가 필요하다. 자원 정보 검색을 위해서는 모니터링이 전체 자원에서 일어나야 하므로 이에 따른 오버헤드가 예상된다. 본 논문에서는 모니터링의 오버헤드를 줄이면서도 효율적으로 정확하게 자원 정보를 수집 할 수 있는 모니터링 기술을 구현하였다. 여기서 제안된 모니터링 기술은 시스템 성능에 따라 자동적으로 모니터링 주기를 조절하게 된다. 이를 통해 모니터링에 의한 오버헤드가 줄었음을 측정 결과를 통해 보일 것이다.