• 제목/요약/키워드: Stationary Grid

검색결과 66건 처리시간 0.028초

Computed Radiography에서 고정형 그리드와 이동형 그리드 영상의 인식률 비교 (Stationary and Moving Computed Radiography Grids : Comparative Observer's Perception)

  • 이기호;이창훈;진계환
    • 한국방사선학회논문지
    • /
    • 제9권7호
    • /
    • pp.515-521
    • /
    • 2015
  • 고정형 그리드(stationary grid)에서 그리드 아티팩트(grid artifacts)와 모아레 아티팩트($moir{\acute{e}}$ pattern artifacts)로 인한 영상의 질의 저하와 이동형 그리드(moving grid)에서의 컷 오프 아티팩트(cut off artifacts)로 인한 영상의 질의 저하를 정량적으로 비교 평가하였다. CDRAD 팬텀(Phantom)과 두께 24 cm의 acryl Phantom을 촬영조건(X-ray exposure conditions)을 100 cm, 80 kVp, 30 mA로 하여 고정형 그리드와 이동형그리드에서 영상(X-ray imaging)을 획득하였다. CDRAD Analyser을 이용한 영상(X-ray imaging) 인식률(observer's perception)은 고정그리드에서 평균(mean) 49.36, 표준편차(standard deviation) 3.76, 최대값(max) 55.56, 최소값 38.67이었고 이동형그리드에서 평균 47.04, 편차 12.69, 최대값 55.56, 최소값 20.89이었다. 이동형 그리드보다 고정형 그리드가 인식률의 평균과 표준편차에서 더 우수하게 나타났다.

계통 연계형 인버터의 정지좌표전류제어 및 외란제거 제어알고리즘 설계 (Design of stationary reference frame current and disturbance rejection control algorithms for a grid connected inverter)

  • 김성현;이재석
    • 전기전자학회논문지
    • /
    • 제24권1호
    • /
    • pp.154-160
    • /
    • 2020
  • 본 논문에서는 계통연계인버터용 정지좌표기반 전류제어알고리즘을 제안한다. PI 제어기는 계통 연결 인버터의 전류 제어기로 사용되고 있다. 정지좌표기반 PI 제어기를 사용할 경우, AC 신호 제어로 인하여 정상 상태 오류와 위상지연현상이 발생한다. 본 논문에서는 전향보상기를 추가하여 명령 추적 성능을 높이고 과도 응답을 개선하는 방법을 제안한다. 또한 계통 전압을 외란으로 사용하여 계통 오류 발생 시 시스템을 보호하기 위해 외란을 측정 및 제거하는 제어 방법을 제안한다. 제안된 제어 방법은 수학적으로 유도하고 전달 함수로 표현하였으며 시뮬레이션을 통하여 검증하였다.

Stationary Frame Current Control Evaluations for Three-Phase Grid-Connected Inverters with PVR-based Active Damped LCL Filters

  • Han, Yang;Shen, Pan;Guerrero, Josep M.
    • Journal of Power Electronics
    • /
    • 제16권1호
    • /
    • pp.297-309
    • /
    • 2016
  • Grid-connected inverters (GCIs) with an LCL output filter have the ability of attenuating high-frequency (HF) switching ripples. However, by using only grid-current control, the system is prone to resonances if it is not properly damped, and the current distortion is amplified significantly under highly distorted grid conditions. This paper proposes a synchronous reference frame equivalent proportional-integral (SRF-EPI) controller in the αβ stationary frame using the parallel virtual resistance-based active damping (PVR-AD) strategy for grid-interfaced distributed generation (DG) systems to suppress LCL resonance. Although both a proportional-resonant (PR) controller in the αβ stationary frame and a PI controller in the dq synchronous frame achieve zero steady-state error, the amplitude- and phase-frequency characteristics differ greatly from each other except for the reference tracking at the fundamental frequency. Therefore, an accurate SRF-EPI controller in the αβ stationary frame is established to achieve precise tracking accuracy. Moreover, the robustness, the harmonic rejection capability, and the influence of the control delay are investigated by the Nyquist stability criterion when the PVR-based AD method is adopted. Furthermore, grid voltage feed-forward and multiple PR controllers are integrated into the current loop to mitigate the current distortion introduced by the grid background distortion. In addition, the parameters design guidelines are presented to show the effectiveness of the proposed strategy. Finally, simulation and experimental results are provided to validate the feasibility of the proposed control approach.

H.264/AVC 움직임 추정을 위한 효율적인 정적 블록 스킵 방법과 결합된 다이아몬드 웹 격자 탐색 알고리즘 (A Diamond Web-grid Search Algorithm Combined with Efficient Stationary Block Skip Method for H.264/AVC Motion Estimation)

  • 정창욱;최진구;이케나가 다케시;고토 사토시
    • 인터넷정보학회논문지
    • /
    • 제11권2호
    • /
    • pp.49-60
    • /
    • 2010
  • H.264/AVC 표준은 여러 가지 신기술들을 접목시킴으로써 기존의 동영상 표준들보다 한층 개선된 부호화 효율성을 제공한다.하지만, H.264/AVC 인코더의 향상된 부호화 기술은 그것의 전반적인 복잡도를 크게 증가시켰다. 따라서, 인코더의 복잡도 수준을 경감시키기 위한 최적화의 연구는 중대한 선결 과제이다. 특히, 움직임 추정 부분에 대한 계산량의 비율은 인코더의 작업시간을 크게 좌우한다. 본 논문에서는 완전 다이아몬드와 12각형을 기본 탐색 패턴으로 사용하고 특정한 임계기준치를 적용시킴으로써 효율적으로 정적 블록들을 스킵하는 다이아몬드 웹 격자 탐색 알고리즘을 제안한다. 실험 결과는 본 논문에서 제안된 기법이 기존의 UMHexagonS 알고리즘의 계산량을 12%까지 감소시키면서도 유사한 PSNR을 유지한다는 것을 보여준다.

CFD PARAMETRIC STUDY FOR 2D WATER ENTRY

  • Lee, H.H.;Rhee, S.H.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 2009년 춘계학술대회논문집
    • /
    • pp.191-195
    • /
    • 2009
  • A parametric study for for the water entry of a two dimensional symmetric wedge with deadrise angle of 10 degrees was carried out to find out the most dominant parameter. Water entry problem with constant velocity is simplified as the stationary wedge in the way of the upcoming water surface. The calculated impact loads showed that the effect of the viscosity was not so important in this problem. For a given grid system a suitable time step size can be found. The most sensitive parameter was found to be the grid size.

  • PDF

Performance Improvement of Grid-Connected Inverter Systems under Unbalanced and Distorted Grid Voltage by Using a PR Controller

  • Lee, Jong-Hyun;Jeong, Hae-Gwang;Lee, Kyo-Beum
    • Journal of Electrical Engineering and Technology
    • /
    • 제7권6호
    • /
    • pp.918-925
    • /
    • 2012
  • This paper proposes a control method for grid-connected inverter systems under unbalanced and distorted grid voltage. The proposed method can reduce the power ripple caused by the unbalanced condition and compensate for the low-order harmonics of the output currents caused by the distortion of grid voltage. To reduce the power ripple, our method replaces the two conventional PI controllers with one PR controllers in the stationary frame. PR controllers can implement selective harmonic compensation without excessive computational requirements; the use of these controllers simplifies the method. Both the simulated and experimental results agree well with the theoretical analysis.

A grid-line suppression technique based on the nonsubsampled contourlet transform in digital radiography

  • Namwoo Kim;Taeyoung Um;Hyun Tae Leem;Bon Tack Koo;Kyuseok Kim;Kyu Bom Kim
    • Nuclear Engineering and Technology
    • /
    • 제55권2호
    • /
    • pp.655-668
    • /
    • 2023
  • In radiography, an antiscatter grid is a well-known device for eliminating unexpected x-ray scatter. We investigate a new stationary grid artifact suppression method based on a nonsubsampled contourlet transform (NSCT) incorporated with Gaussian band-pass filtering. The proposed method has an advantage that extracts the Moiré components while minimizing the loss of image information and apply the prior information of Moiré component positions in multi-decomposition sub-band images. We implemented the proposed algorithm and performed a simulation and an experiment to demonstrate its viability. We did this experiment using an x-ray tube (M-113T, Varian, focal spot size: 0.1 mm), a flat-panel detector (ROSE-M Sensor, Aspenstate, pixel dimension: 3032 × 3800 pixels, pixel size: 0.076 mm), and carbon graphite-interspaced grids (JPI Healthcare, 18 cm × 24 cm, line density: 103 LP/inch and 150 LP/inch, ratio: 5:1, focal distance: 65 cm). Our results indicate that the proposed method successfully suppressed grid artifacts by reducing them without either reducing the spatial resolution or causing negative side effects. Consequently, we anticipate that the proposed method can improve image acquisition in a stationary grid x-ray system as well as in extended x-ray imaging.

보존적 중첩격자기법을 이용한 동적 플랩의 천이적 공력거동에 관한 수치적 연구 (Numerical Study on Transient Aerodynamics of Moving Flap Using Conservative Chimera Grid Method)

  • 최성욱;장근식;김인선
    • 한국전산유체공학회지
    • /
    • 제5권2호
    • /
    • pp.9-19
    • /
    • 2000
  • Transient aerodynamic response of an airfoil to a moving plane-flap is numerically investigated using the two-dimensional Euler equations with conservative Chimera grid method. A body moving relative to a stationary grid is treated by an overset grid bounded by a 'Dynamic Domain Dividing Line' which has an advantage for constructing a well-defined hole-cutting boundary. A conservative Chimera grid method with the dynamic domain-dividing line technique is applied and validated by solving the flowfield around a circular cylinder moving supersonic speed. The unsteady and transient characteristics of the flow solver are also examined by computations of an oscillating airfoil and a ramp pitching airfoil respectively. The transient aerodynamic behavior of an airfoil with a moving plane-flap is analyzed for various flow conditions such as deflecting rate of flap and free stream Mach number.

  • PDF

보존적 중첩격자기법을 이용한 동적 플랩의 천이적 공력거동에 관한 수치적 연구 (Numerical Study on Transient Aerodynamics of Moving Flap Using Conservative Chimera Grid Method)

  • 최성욱;장근식
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 1999년도 추계 학술대회논문집
    • /
    • pp.85-94
    • /
    • 1999
  • Transient aerodynamic response of an airfoil to a moving plane-flap is numerically investigated using two-dimensional Euler equations with conservative Chimera grid method. A body moving relative to a stationary grid is treated by an overset grid bounded by a 'dynamic domain-dividing line' the concept of which is developed in this study. A conservative Chimera grid method with a dynamic domain-dividing line technique is applied and validated by solving the flowfield around circular cylinder moving supersonic speed. The unsteady and transient characteristics of the flow solver is also examined by computations of a oscillating airfoil and a ramp pitching airfoil respectively. The transient aerodynamic behavior of an airfoil with a moving plane-flap is analyzed for various flow conditions such as deflecting rate of flap and free stream Mach number.

  • PDF

고정 그리드를 사용한 디지털 방사선 영상에서 1차원 필터에 기초한 왜곡의 제거 (Artifact Reduction in Digital Radiography Images with the Stationary Grid Based on 1-Dimensional Filters)

  • 김동식
    • 대한전자공학회논문지SP
    • /
    • 제47권5호
    • /
    • pp.117-126
    • /
    • 2010
  • 산란선을 흡수하여 보다 선명한 x선 영상을 얻기 위하여 산란방지 그리드를 사용하여 투사영상을 얻는데, 이때 그리드로 인한 왜곡이 발생한다. 본 논문에서는 회전된 그리드를 사용하여 투사영상을 얻고 단순한 1차원 저역필터를 영상의 공간영역에서 각 축으로 별도로 적용하여 그리드 왜곡을 효율적으로 제거하는 방법을 제안하고 그 성능을 고찰해 보았다. 제안한 방법은 왜곡 주파수를 별도로 예측할 필요 없이, 회전된 그리드를 사용하여 획득한 영상에 단순한 1차원 필터를 주파수영역이 아닌 공간영역에서 적용하므로 매우 단순하여 쉽게 구현이 가능하며 빠른 계산 속도를 가지는 장점을 가지고 있으면서 그 성능은 주파수영역에서 2차원 필터를 적용한 경우와 유사하다.