• 제목/요약/키워드: distortion grid

검색결과 184건 처리시간 0.034초

d-q 변환에서의 고조파 맥동 제거 (A Rejection of Harmonic Ripples for d-q Transformation)

  • 최남열;이치환
    • 조명전기설비학회논문지
    • /
    • 제29권12호
    • /
    • pp.83-87
    • /
    • 2015
  • This paper presents a simple notch filter, which is so suitable for three-phase unbalanced and distorted power line. In the d-q synchronous transformation, three-phase unbalanced and distorted voltages generate lots of ripple voltages on d-q axes. The ripples make disturbances on controllers such as PLL of phase tracking. Unbalanced state makes ripple of double the frequency of power line. Odd harmonics 5th and 7th on the line make even 4th and 6th ripples on d-q axes due to the rotating reference frame, respectively. Cascaded two comb filters, delay lines 1/4T and 1/8T, are adopted for the ripple rejection. The filter rejects harmonics 2nd, 4th, 6th, 10th and so on. They are very effective to remove the ripples of both unbalance and distortion. The filter, implemented by two FIFOs on an experimental system, is adopted on a PLL controller of power line phase tracking. Through the simulation and experimental results, performance of the proposed comb filter has been validated.

Robust Deadbeat Current Control Method for Three-Phase Voltage-Source Active Power Filter

  • Nishida, Katsumi;Ahmed, Tarek;Nakaoka, Mutsuo
    • Journal of Power Electronics
    • /
    • 제4권2호
    • /
    • pp.102-111
    • /
    • 2004
  • This paper is concerned with a deadbeat current control implementation of shunt-type three-phase active power filter (APF). Although the one-dimensional deadbeat control method can attain time-optimal response of APF compensating current, one sampling period is actually required fur its settling time. This delay is a serious drawback for this control technique. To cancel such a delay and one more delay caused by DSP execution time, the desired APF compensating current has to be predicted two sampling periods ahead. Therefore an adaptive predictor is adopted for the purpose of both predicting the control error of two sampling periods ahead and bringing the robustness to the deadbeat current control system. By adding the adaptive predictor output as an adjustment term to the reference value of half a source voltage period before, settling time is made short in a transient state. On the other hand, in a steady state, THD (total harmonic distortion) of the utility grid side AC source current can be reduced as much as possible, compared to the case that ideal identification of controlled system could be made.

연락공 형상에 따른 와류실식 디젤기관의 유동 특성 수치해석 (Numerical Analysis of Flow Characteristics in Swirl Chamber Type Diesel Engine)

  • 권태윤;최경호
    • 한국자동차공학회논문집
    • /
    • 제13권4호
    • /
    • pp.49-57
    • /
    • 2005
  • In this study, in-cylinder flow of the swirl chamber type diesel engine numerically simulated by VECTIS code. The flow fields during the intake and compression process were also investigated in detail. Numerical results revealed that the generation and distortion of the swirling, tumbling vortices and those influences on turbulence kinetic energy by shape of the jet passage, angle and area. It was also found that flow characteristics were affected by inflow velocity that depends on change of the jet passage shape. Swirl ratio was increased according to decrease of jet passage area, and was affected by piston motion according to increase of jet passage angle. Tumbling vortices had the similar in various cases, but tumble ratio was increased with the inflow velocity. The generation of turbulence kinetic energy was considerably influenced by complex effects of swirling and tumbling vortices.

다양한 일사량 조건에서의 PV-AF 시스템의 특성에 관한 연구 (A Study on the Performance Analysis of the PV-AF System under various Irradiation Conditions)

  • 서효룡;김경훈;박민원;유인근
    • 대한전기학회:학술대회논문집
    • /
    • 대한전기학회 2007년도 제38회 하계학술대회
    • /
    • pp.212-213
    • /
    • 2007
  • Grid-connected PV(Photovoltaic) power generation system has experienced increasing attention in recent years. But the growing number of non-linear equipments, such as, inverters, has been demanding the compensation for the disturbances caused by them. These non-linear loads may cause poor power factor and high degree of harmonics. Installation of an AF(active filter) can be one of the solutions to mitigate the line distortion, but it requires additional costs. On the other hand, many PV systems have been interconnected to the distribution system. So, the PV system combined with the function of the active filter system can be useful for the application in the power distribution system. In this paper, PV-AF system using DSP (Digital Signal Processing) controller confirmed that it is possible to combine the AF theory to the three phase PV system connected to the utility under various irradiation conditions.

  • PDF

Parallel Control of Shunt Active Power Filters in Capacity Proportion Frequency Allocation Mode

  • Zhang, Shuquan;Dai, Ke;Xie, Bin;Kang, Yong
    • Journal of Power Electronics
    • /
    • 제10권4호
    • /
    • pp.419-427
    • /
    • 2010
  • A parallel control strategy in capacity proportion frequency allocation mode for shunt active power filters (APFs) is proposed to overcome some of the difficulties in high power applications. To improve the compensation accuracy and overall system stability, an improved selective harmonic current control based on multiple synchronous rotating reference coordinates is presented in a single APF unit, which approximately implements zero steady-state error compensation. The combined decoupling strategy is proposed and theoretically analyzed to simplify selective harmonic current control. Improved selective harmonic current control forms the basis for multi-APF parallel operation. Therefore, a parallel control strategy is proposed to realize a proper optimization so that the APFs with a larger capacity compensate more harmonic current and the ones with a smaller capacity compensate less harmonic current, which is very practical for accurate harmonic current compensation and stable grid operation in high power applications. This is verified by experimental results. The total harmonic distortion (THD) is reduced from 29% to 2.7% for a typical uncontrolled rectifier load with a resistor and an inductor in a laboratory platform.

PV-AF시스템에서 단독운전 방지기법 및 기존 단독운전 방지기법의 시뮬레이션 해석 및 비교 (A Simulation for Anti-islanding Method in PV-AF System and Existing Anti-islanding Method)

  • 김경훈;서효룡;이석주;박민원;유인근;전진홍;김슬기;안종보
    • 대한전기학회:학술대회논문집
    • /
    • 대한전기학회 2007년도 제38회 하계학술대회
    • /
    • pp.206-207
    • /
    • 2007
  • Islanding is the electrical phenomenon in a part of a power network disconnected from the utility, where the loads are entirely supplied by PV systems, and where the voltage and frequency are maintained around nominal values. But islanding may result in power-quality issues, interference to grid-protection devices, equipment damage, and even personnel safety hazards[4]. Therefore, islanding must be detected and stopped. The existing anti-islanding methods have NDZ(None-detection Zone) or power quality degradation. But PV-AF power generation system has the function of not only shunt active filter but also anti-islanding method without NDZ. In this paper, It is proved that PV-AF system has originally the function of anti-islanding without not only NDZ and but current distortion

  • PDF

Scheme for Reducing Harmonics in Output Voltage of Modular Multilevel Converters with Offset Voltage Injection

  • Anupom, Devnath;Shin, Dong-Cheol;Lee, Dong-Myung
    • Journal of Power Electronics
    • /
    • 제19권6호
    • /
    • pp.1496-1504
    • /
    • 2019
  • This paper proposes a new THD reduction algorithm for modular multilevel converters (MMCs) with offset voltage injection operated in nearest level modulation (NLM). High voltage direct current (HVDC) is actively introduced to the grid connection of offshore wind powers, and this paper deals with a voltage generation technique with an MMC for wind power generation. In the proposed method, third harmonic voltage is added for reducing the THD. The third harmonic voltage is adjusted so that each of the pole voltage magnitudes maintains a constant value with a maximum number of (N+1) levels, where N is the number of sub-modules per arm. By using the proposed method, the THD of the output voltage is mitigated without increasing the switching frequency. In addition, the proposed method has advantageous characteristics such as simple implementation. As a part of this study, this paper compares the THD results of the conventional method and the proposed method with offset voltage injection to reduce the THD. In this paper, simulations have been carried out to verify the effectiveness of the proposed scheme, and the proposed method is implemented by a HILS (Hardware in the Loop Simulation) system. The obtained results show agreement with the simulation results. It is confirmed that the new scheme achieved the maximum level output voltage and improved the THD quality.

스마트폰 실내 위치 추적을 위한 지자기 센서 보정에 관한 연구 (A Study on magnetic sensor calibration for indoor smartphone position tracking)

  • 이동욱;오종택
    • 한국인터넷방송통신학회논문지
    • /
    • 제18권6호
    • /
    • pp.229-235
    • /
    • 2018
  • 스마트폰을 이용한 실내 위치 추적 기술에 관한 연구가 활발하게 진행되고 있다. 특히 스마트폰의 이동 경로를 지도에 표시하기 위해서는 대부분의 스마트폰에 내장되어 있는 지자기 센서를 이용하여 방위각을 추정해야 하는데, 주변의 쇠구조물에 의한 자기장의 왜곡과 스마트폰의 기울어짐 때문에 방위각 추정 오차가 발생한다. 본 논문에서는 정지 상태에서의 지자기 센서의 보정 방법과 스마트폰의 기울어짐에 대한 보정 방법을 제시한다. 또한 스마트폰에서 자북과 도북의 차이에 의한 방위각 오차를 보정하는 방법을 제안한다.

Numerical investigation on the wave interferences of submerged bodies operating near the free surface

  • Li, Dong;Yang, Qun;Zhai, Lin;Wang, Zhen;He, Chuan-lin
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • 제13권1호
    • /
    • pp.65-74
    • /
    • 2021
  • A key factor that governs the wave interferences of a submerged body is the dimensionless Froude number. Computational Fluid Dynamics (CFD) is used to describe the resistance force coefficients and the generated waves of two SUBOFF submarine models. Grid independence studies are performed on two cases, totally and shallowly submerged cases, with four sets of computing meshes. The highest peaks are marked by red points at given wavelengths, a line is fitted to those points with a least-squares approximation, and the half wake angle at multiple Froude numbers is defined between the fitted line and the centerline of the free surface. The results show that when the depth of the target is 1.1D, constructive interferences occur at Fn = 0.3 and 0.5, while destructive interference occurs at Fn = 0.35 with distortion of the waveform. The half wake angle is less than 19.47° because of the interference between the bow and stern wave systems.

가려짐 영역 검출 및 스테레오 영상 내의 특징들을 이용한 다시점 영상 생성 (Multi-view Image Generation from Stereoscopic Image Features and the Occlusion Region Extraction)

  • 이왕로;고민수;엄기문;정원식;허남호;유지상
    • 방송공학회논문지
    • /
    • 제17권5호
    • /
    • pp.838-850
    • /
    • 2012
  • 본 논문에서는 스테레오 영상에서 얻은 다양한 특징들을 이용하여 다시점 영상을 생성하는 방법을 제안한다. 제안된 기법에서는 먼저 주어진 스테레오 영상에서 명암변화 주목도 지도(intensity gradient saliency map)를 생성한다. 다음으로 좌우 영상 간에 블럭 단위의 움직임을 나타내는 광류(optical flow)를 계산하고 scale-invariant feature transform(SIFT) 기법을 통해 사물의 크기와 회전에 변하지 않는 영상의 특징 점을 구하여 이 특징점 간의 변이를 구한 다음, 이 두 변이 정보들을 결합하여 변이 주목도 지도(disparity saliency map)를 생성 한다. 생성된 변이 주목도 지도는 가려짐 영역 검출을 통해 오류 변이가 제거된다. 세 번째로 영상 워핑시에 직선의 왜곡을 최소화하기 위해 직선 세그먼트를 얻는다. 마지막으로 다시점 영상은 이렇게 추출된 영상 특징들을 제한 조건으로 사용하여 그리드 메쉬(grid-mesh) 기반 영상 워핑(warping) 기법에 의해 생성된다. 실험 결과를 통해 제안한 기법으로 생성된 다시점 영상의 화질이 기존 DIBR 기법보다 우수한 것을 확인할 수 있었다.