• 전력전자학회논문지
• /
• 제23권5호
• /
• pp.336-344
• /
• 2018

This study proposes a new PWM method for leakage current reduction and neutral point (NP) current control in three-phase three-level converter employed in bipolar DC distribution systems. The proposed PWM method uses medium vectors only when there is no need to control the NP current. Thus, common mode voltages are held constant to realize zero leakage current. Some space vectors that produce low-frequency common mode voltages are employed to minimize leakage currents when the average NP current needs to be a positive or negative value. The proposed space vector PWM is implemented based on barycentric coordinate. The validity of the proposed PWM method is verified by simulations and experiments.

• 한국정보통신학회논문지
• /
• 제10권10호
• /
• pp.1848-1853
• /
• 2006

본 논문에서는 3차원 집적 영상 기술에서 렌즈배열 모델을 적용하여 컴퓨터적으로 해상도가 개선된 3차원 영상을 재생하는 방법을 제안하고, 그 성능을 분석한다. 기존의 보고된 컴퓨터 적 시점 재생 방법은 핀홀 배열 모델에 기초하지만, 제안하는 방법은 렌즈 배열 모델을 적용하기 때문에 동일한 요소영상에서 다수의 픽셀을 추출하여 높은 해상도를 얻을 수 있다. 제안한 방법의 유용함을 보이기 위해 기초적인 실험을 수행하고 그 결과를 보고한다.

• Journal of Power Electronics
• /
• 제16권4호
• /
• pp.1306-1315
• /
• 2016

Modern power systems driven by high-power converters have become inevitable in view of the ever increasing demand for electric power. The total power loss can be reduced by limiting the switching losses in such power converters; increased power efficiency can thus be achieved. A reduced switching frequency that is less than a few hundreds of hertz is applied to power converters that produce output waveforms with high distortion. Selective harmonic elimination pulse width modulation (SHEPWM) is an optimized low switching frequency pulse width modulation method that is based on offline estimation. This method can pre-program the harmonic profile of the output waveform over a range of modulation indices to eliminate low-order harmonics. In this paper, a SHEPWM scheme for three-phase three-leg neutral point clamped inverter is proposed. Aside from eliminating the selected harmonics, the DC capacitor voltages at the DC bus are also balanced because of the symmetrical pulse pattern over a quarter cycle of the period. The technique utilized in the estimation of switching angles involves the firefly algorithm (FA). Compared with other techniques, FA is more robust and entails less computation time. Simulation in the MATLAB/SIMULINK environment and experimental verification in the very large scale integration platform with Spartan 6A DSP are performed to prove the validity of the proposed technique.

• 미술이론과 현장
• /
• 제7호
• /
• pp.165-188
• /
• 2009

In the development of linear perspective, Brook Taylor's theory has achieved a special position. With his method described in Linear Perspective(1715) and New Principles of Linear Perspective(1719), the subject of linear perspective became a generalized and abstract theory rather than a practical method for painters. He is known to be the first who used the term 'vanishing point'. Although a similar concept has been used form the early stage of Renaissance linear perspective, he developed a new method of British perspective technique of measure points based on the concept of 'vanishing points'. In the 15th and 16th century linear perspective, pictorial space is considered as independent space detached from the outer world. Albertian method of linear perspective is to construct a pavement on the picture in accordance with the centric point where the centric ray of the visual pyramid strikes the picture plane. Comparison to this traditional method, Taylor established the concent of a vanishing point (and a vanishing line), namely, the point (and the line) where a line (and a plane) through the eye point parallel to the considered line (and the plane) meets the picture plane. In the traditional situation like in Albertian method, the picture plane was assumed to be vertical and the center of the picture usually corresponded with the vanishing point. On the other hand, Taylor emphasized the role of vanishing points, and as a result, his method entered the domain of projective geometry rather than Euclidean geometry. For Taylor's theory was highly abstract and difficult to apply for the practitioners, there appeared many perspective treatises based on his theory in England since 1740s. Joshua Kirby's Dr. Brook Taylor's Method of Perspective Made Easy, Both in Theory and Practice(1754) was one of the most popular treatises among these posterior writings. As a well-known painter of the 18th century English society and perspective professor of the St. Martin's Lane Academy, Kirby tried to bridge the gap between the practice of the artists and the mathematical theory of Taylor. Trying to ease the common readers into Taylor's method, Kirby somehow abbreviated and even omitted several crucial parts of Taylor's ideas, especially concerning to the inverse problems of perspective projection. Taylor's theory and Kirby's handbook reveal us that the development of linear perspective in European society entered a transitional phase in the 18th century. In the European tradition, linear perspective means a representational system to indicated the three-dimensional nature of space and the image of objects on the two-dimensional surface, using the central projection method. However, Taylor and following scholars converted linear perspective as a complete mathematical and abstract theory. Such a development was also due to concern and interest of contemporary artists toward new visions of infinite space and kaleidoscopic phenomena of visual perception.

• ETRI Journal
• /
• 제39권2호
• /
• pp.181-190
• /
• 2017

The movements of the human body are difficult to capture owing to the complexity of the three-dimensional skeleton model and occlusion problems. In this paper, we propose a motion capture system that tracks dynamic human motions in real time. Without using external markers, the proposed system adopts multiple depth sensors (Microsoft Kinect) to overcome the occlusion and body rotation problems. To combine the joint data retrieved from the multiple sensors, our calibration process samples a point cloud from depth images and unifies the coordinate systems in point clouds into a single coordinate system via the iterative closest point method. Using noisy skeletal data from sensors, a posture reconstruction method is introduced to estimate the optimal joint positions for consistent motion generation. Based on the high tracking accuracy of the proposed system, we demonstrate that our system is applicable to various motion-based training programs in dance and Taekwondo.

• 한국통신학회논문지
• /
• 제16권12호
• /
• pp.1236-1248
• /
• 1991

행렬 분해방식에 의한 새로운 고속 DCT 연산 방법을 유도하였다. N점 DCT변환을 N/2점 DCT 변환과 2개의 N/4점 변환들로 얻을수 있었다. 이 방법은 곱셈작용이 대부분 신호 흐름도상의 출력단에 가깝게 있게 되어 유한길이 연산인 경우에 발생하는 반올림 오차량이 기존의 Lee와 Chen 방법에 비하여 배우 적다는 점이 장점이다. 그리고 곱셈작용의 위치는 다르지만 동일 연산량을 갖는 또다른 3개의 DCT 행렬분해 결과도 보였다.

• 한국도로학회논문집
• /
• 제13권4호
• /
• pp.177-185
• /
• 2011

터널, 교량, 커브구간 등 교통사고위험이 연속적으로 존재하는 도로구간에서의 대형교통사고를 예방하기 위하여 경찰청은 2007년 1월 위험도로구간에서 교통관리 대책의 일환으로서 무인구간속도위반단속시스템 시범설치 운영을 결정하였다. 2007년 12월 영동고속도로 둔내터널 강릉방면을 시작으로 2011년 7월 현재까지 고속도로 8개 구간 및 국도 3개 구간, 총 11개 구간 85km에서 무인구간속도위반단속시스템이 운영 중에 있다. 하지만 이러한 무인구간단속시스템의 설치가 교통사고 감소에 얼마나 기여하는지에 대한 실질적인 연구가 부족하였다. 따라서 본 연구에서는 고속도로를 중심으로 무인구간속도위반단속시 스템 설치 전 후 교통사고건수를 체계적으로 비교할 수 있는 비교그룹방법을 이용하여 무인구간속도위반단속시스템의 설치효과를 분석하고자 한다. 이를 위하여 2008년 고속도로에 설치된 무인구간속도위반단속시스템을 대상으로 설치 전 후 각 1년의 사고이력자료를 수집하여 분석하였다. 그 결과, 무인구간속도위반단속시스템을 설치하지 않았을 경우에 비해 사업을 시행함으로서 49.97% 사고감소효과가 있는 것으로 나타났다.

• Communications for Statistical Applications and Methods
• /
• 제9권2호
• /
• pp.389-399
• /
• 2002

In order to examine whether the difference between two point estimates of population proportions is statistically significant, data analysts use two techniques. The first is to explore the overlap between two associated confidence intervals. Second method is to test the significance which is introduced at most statistical textbooks under the common assumptions of consistency, asymptotic normality, and asymptotic independence of the estimates. Under the null hypothesis which is two population proportions are equal, the pooled estimator of population proportion is preferred as a point estimator since two independent random samples are considered to be collected from one population. Hence as an alternative method, we could obtain another confidence interval of the difference of the population proportions with using the pooled estimate. We conclude that, among three methods, the overlapped method is under-estimated, and the difference of the population proportions method is over-estimated on the basis of the proposed method.

• 대한전기학회논문지:전력기술부문A
• /
• 제48권8호
• /
• pp.958-964
• /
• 1999

The distance in load parameter space to the closest saddle node bifurcation (CSNB) point provides the worst case power margin to voltage instability and the left eigenvector at CSNB identifies the most effective direction to steer the system to maximize voltage stability under contingency. This paper presents an improved direct method for computing CSNB: the order of nonlinear systems equations is reduced to about twice of the size of load flow equations in contrast to about three-times in Dobson's direct method; the initial guess for the direct method is computed efficiently and robustly by combined use of continuation power flow, a pair of multiple load flow solution with Lagrange interpolation. It is also shown that voltage stability may be enhanced significantly with shift of generations in the direction of the left eigenvector at CSNB.

• International Journal of Aeronautical and Space Sciences
• /
• 제18권3호
• /
• pp.403-413
• /
• 2017

Dual-point aerodynamic design optimization is conducted for DLR-F6 wing-body-nacelle-pylon configuration adopting an efficient surface mesh movement method for complex junction geometries. A three-dimensional unstructured Euler solver and its discrete adjoint code are utilized for flow and sensitivity analysis, respectively. Considered design conditions are a low-lift condition and a cruise condition in a transonic regime. Design objective is to minimize drag and reduce shock strength at both flow conditions. Shape deformation is made by variation of the section shapes of inboard wing and pylon, nacelle vertical location and nacelle pitch angle. Hicks-Henne shape functions are employed for deformation of the section shapes of wing and pylon. By the design optimization, drag coefficients were remarkably reduced at both design conditions retaining specified lift coefficient and satisfying other constraints. Two-point design results show mixed features of the one-point design results at low-lift condition and cruise conditions.