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  • Title/Summary/Keyword: Fundamental component

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An Analytic Method for Measuring Accurate Fundamental Frequency Components (기본파 성분의 정확한 측정을 위한 해석적 방법)

  • Nam, Sun-Yeol;Gang, Sang-Hui;Park, Jong-Geun
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.51 no.4
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    • pp.175-182
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    • 2002
  • This paper proposes an analytic method for measuring the accurate fundamental frequency component of a fault current signal distorted with a DC-offset, a characteristic frequency component, and harmonics. The proposed algorithm is composed of four stages: sine filer, linear filter, Prony's method, and measurement. The sine filter and the linear filter eliminate harmonics and the fundamental frequency component, respectively. Then Prony's method is used to estimate the parameters of the DC-offset and the characteristic frequency component. Finally, the fundamental frequency component is measured by compensating the sine-filtered signal with the estimated parameters. The performance evaluation of the proposed method is presented for a-phase to around faults on a 345 kV 200 km overhead transmission line. The EMTP is used to generate fault current signals under different fault locations and fault inception angles. It is shown that the analytic method accurately measures the fundamental frequency component regardless of the characteristic frequency component as well as the DC-offset.

Effects of Input Harmonics, DC Offset and Step Changes of the Fundamental Component on Single-Phase EPLL and Elimination

  • Luo, Linsong;Tian, Huixin;Wu, Fengjiang
    • Journal of Power Electronics
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    • v.15 no.4
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    • pp.1085-1092
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    • 2015
  • In this paper, the expressions of the estimated information of a single-phase enhanced phase-locked loop (EPLL), when input signal contains harmonics and a DC offset while the fundamental component takes step changes, are derived. The theoretical analysis results indicate that in the estimated information, the nth-order harmonics cause n+1th-order periodic ripples, and the DC offset causes a periodic ripple at the fundamental frequency. Step changes of the amplitude, phase angle and frequency of the fundamental component cause a transient periodic ripple at twice the frequency. These periodic ripples deteriorate the performance of the EPLL. A hybrid filter based EPLL (HF-EPLL) is proposed to eliminate these periodic ripples. A delay signal cancellation filter is set at the input of the EPLL to cancel the DC offset and even-order harmonics. A sliding Goertzel transform-based filter is introduced into the amplitude estimation loop and frequency estimation loop to eliminate the periodic ripples caused by the residual input odd-order harmonics and step change of the input fundamental component. The parameter design rules of the two filters are discussed in detail. Experimental waveforms of both the conventional EPLL and the proposed HF-EPLL are given and compared with each other to verify the theoretical analysis and advantages of the proposed HF-EPLL.

An Over Current Protection Scheme for Hybrid Active Power filter

  • Lee Woo-Cheol;Chae Beom-Seok;Hyun Dong-Seok;Lee Taeck-Kie
    • Proceedings of the KIPE Conference
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    • 2001.10a
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    • pp.571-575
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    • 2001
  • A protection scheme for hybrid active power filters, which is combined shunt passive filter and small rated series active filter, is presented and analyzed in this paper. The proposed series active power filter operated as a high impedance 'k(Ω)' to the fundamental component when over current occurs in the power distribution system, and three control strategies are proposed in this paper. The first is the method by detecting the fundamental source current through the p-q theory, the second is the method by detecting the fundamental component of load current in Synchronous Reference Frame (SRF) and the third is the method by detecting the input voltage. When the over current occurs in the power distribution system, the proposed scheme protects the series active power filter without additional protection circuits. The validity of proposed protection scheme is investigated through experimental result for the prototype hybrid active power filter system.

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Double Frequency Forcing of the Laminar Separated Flow over a Backward-Facing Step (층류박리 후향계단 유동의 이중주파수 가진)

  • Kim, Sung-Wook;Choi, Hae-Cheon;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.8
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    • pp.1023-1032
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    • 2003
  • The effect of local forcing on the separated flow over a backward-facing step is investigated through hot-wire measurements and flow visualization with multi-smoke wires. The boundary layer upstream of the separation point is laminar and the Reynolds number based on the free stream velocity and the step height is 13800. The local forcing is given from a slit located at the step edge and the forcing signal is always defined when the wind tunnel is in operation. In case of single frequency forcing, the streamwise velocity and the reattachment length are measured under forcing with various forcing frequencies. For the range of 0.010〈S tθ〈0.013, the forcing frequency component of the streamwise velocity fluctuation grows exponentially and is saturated at x/h = 0.75 , while its subharmonic component grows following the fundamental and is saturated at x/h = 2.0. However, the saturated value of the subharmonic is much lower than that of the fundamental. It is observed that the vortex formation is inhibited by the forcing at S tθ = 0.019 . For double frequency forcing, natural instability frequency is adopted as a fundamental frequency and its subharmonic is superposed on it. The fundamental frequency component of the streamwise velocity grows exponentially and is saturated at 0.5 < x/h < 0.75, while its subharmonic component grows following the fundamental and is saturated at x/h= 1.5 . Furthermore, the saturated value of the subharmonic component is much higher than that for the single frequency forcing and is nearly the same or higher than that of the fundamental. It is observed that the subharmonic component does not grow for the narrow range of the initial phase difference. This means that there is a range of the initial phase difference where the vortex parring cannot be enhanced or amplified by double frequency forcing. In addition, this effect of the initial phase difference on the development of the shear layer and the distribution of the reattachment length shows a similar trend. From these observations, it can be inferred that the development of the shear layer and the reattachment length are closely related to the vortex paring.

A Distance Relaying Algorithm Using an Improved Technique for Removing DC-offset (DC-Offset 제거 기능을 향상시킨 거리계전 알고리즘)

  • No, Jae-Keun;Kang, Sang-Hee;Nam, Soon-Ryul;Park, Jong-Keun
    • Proceedings of the KIEE Conference
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    • 2001.11b
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    • pp.118-120
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    • 2001
  • This paper presents a distance relaying algorithm based on the Discrete Fourier Transform(DFT) for elimination of DC-Offset. When the DFT is applied to current signal. the real and imaginary parts of fundamental component consist of fundamental component itself and DC-Offset. The DC-Offset is calculated by four consecutive values of the imaginary components, so that the fundamental component can be accurately estimated. Performance evaluation is presented for A-phase ground faults on 154kV 80km overhead transmission line. The proposed algorithm is inspected by software simulation and hardware simulation.

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Analysis and Control of Neutral Point Current Deviation in Grid Tied 3-Level NPC Converter under Various Grid Unbalanced Conditions (다양한 불평형 계통 상황에서 계통 연계형 3-레벨 NPC 컨버터의 중성점 전류 변동에 대한 해석 및 제어)

  • Choi, Jaehoon;Suh, Yongsug
    • The Transactions of the Korean Institute of Power Electronics
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    • v.25 no.5
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    • pp.385-393
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    • 2020
  • This study introduces an analysis and control method for the variation of neutral point current in a grid-tied three-level neutral point clamped (NPC) converter under various grid imbalance operating conditions. Various fault cases with unbalanced amplitude and phase are systematically categorized and described using a unified metric called the imbalance factor. The fundamental component of neutral point current is generated under grid imbalance cases. The pattern and behavior of this fundamental component of neutral point current highly depend on the imbalance factor regardless of the particular type of grid fault cases. The control scheme for regulating the negative sequential component of AC input current effectively reduces the size of the fundamental component of neutral point current under a wide range of grid imbalance cases. The control scheme will enable a grid-tied three-level NPC converter to operate reliably and stably under various types of grid faults.

Distance Relaying Algorithm Using a DFT-based Modified Phasor Estimation Method (DFT 기반의 개선된 페이저 연산 기법을 적용한 거리계전 알고리즘)

  • Lee, Dong-Gyu;Kang, Sang-Hee
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.59 no.8
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    • pp.1360-1365
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    • 2010
  • In this paper, we propose a distance relaying algorithm using a Discrete Fourier Transform (DFT)-based modified phasor estimation method to eliminate the adverse influence of exponentially decaying DC offsets. Most distance relays are based on estimating phasors of the voltage and current signals. A DFT is generally used to calculate the phasor of the fundamental frequency component in digital protective relays. However, the output of the DFT contains an error due to exponentially decaying DC offsets. For this reason, distance relays have a tendency to over-reach or under-reach in the presence of DC offset components in a fault current. Therefore, the decaying DC components should be taken into consideration when calculating the phasor of the fundamental frequency component of a relaying signal. The error due to DC offsets in a DFT is calculated and eliminated using the outputs of an even-sample-set DFT and an odd-sample-set DFT, so that the phasor of the fundamental component can be accurately estimated. The performance of the proposed algorithm is evaluated for a-phase to ground faults on a 345 kV, 50 km, simple overhead transmission line. The Electromagnetic Transient Program (EMTP) is used to generate fault signals. The evaluation results indicate that adopting the proposed algorithm in distance relays can effectively suppress the adverse influence of DC offsets.

Phasor Estimation Method Eliminating the Effect of the DC offsets (DC 옵셋의 영향을 제거한 페이저 연산 기법)

  • Lee, Dong-Gyu;Kim, Hyung-Kyu;Kwon, Young-Jin;Kang, Sang-Hee
    • Proceedings of the KIEE Conference
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    • 2009.07a
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    • pp.203_204
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    • 2009
  • In this paper, we propose a Fourier transform-based modified phasor estimation method to eliminate the adverse influence of exponentially decaying DC offsets. Discrete Fourier Transform (DFT) is generally used to calculate the phasor of the fundamental frequency component in digital protective relays. However, the output of the DFT contains an error due to exponentially decaying DC offsets. Therefore, the decaying DC components should be taken into consideration when calculating the phasor of the fundamental frequency component of a relaying signal. In this paper, the error due to DC offsets in a DFT is calculated and eliminated using the outputs of quaternity DFT, so that the phasor of the fundamental component can be accurately estimated. The performance of the proposed algorithm is evaluated by using computer-simulated signals and EMTP-generated signals. A performance evaluation showed that the proposed algorithm was not affected by system and fault conditions. Thus, the proposed algorithm can effectively suppress the adverse influence of DC offsets in a relaying signal.

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A Study on Accurate Phasor Extraction Using a New DC Offset Elimination Filter (새로운 직류 옵셋 제거 필터에 의한 정확한 페이저 추출에 관한 연구)

  • Park, Chul-Won;Yoon, Hee-Whan
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.27 no.7
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    • pp.29-36
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    • 2013
  • In this paper, a new DC offset elimination filter is proposed for an accurate phasor extraction of fundamental frequency component. The proposed method can eliminate a DC offset component which is decayed exponentially. The proposed method uses only one cycle of data for phasor extraction computation, which does not need to preset the time constant of the DC offset component. Also, the other advantages of the proposed method is that gain compensation or phase compensation is not required after filtering. Simulations using ATP were performed to evaluate the performance of the proposed filter method, and the results were compared to the ones obtained by conventional methods.

Object Recognition Using the Edge Orientation Histogram and Improved Multi-Layer Neural Network

  • Kang, Myung-A
    • International Journal of Advanced Culture Technology
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    • v.6 no.3
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    • pp.142-150
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    • 2018
  • This paper describes the algorithm that lowers the dimension, maintains the object recognition and significantly reduces the eigenspace configuration time by combining the edge orientation histogram and principle component analysis. By using the detected object region as a recognition input image, in this paper the object recognition method combined with principle component analysis and the multi-layer network which is one of the intelligent classification was suggested and its performance was evaluated. As a pre-processing algorithm of input object image, this method computes the eigenspace through principle component analysis and expresses the training images with it as a fundamental vector. Each image takes the set of weights for the fundamental vector as a feature vector and it reduces the dimension of image at the same time, and then the object recognition is performed by inputting the multi-layer neural network.