• Title/Summary/Keyword: Harmonic

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ON F-HARMONIC MAPS AND CONVEX FUNCTIONS

  • Kang, Tae-Ho
    • East Asian mathematical journal
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    • v.19 no.2
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    • pp.165-171
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    • 2003
  • We show that any F-harmonic map from a compact manifold M to N is necessarily constant if N possesses a strictly-convex function, and prove 'Liouville type theorems' for F-harmonic maps. Finally, when the target manifold is the real line, we get a result for F-subharmonic functions.

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THE BESOV SPACES OF M-HARMONIC FUNCTIONS

  • Lee, Jin-Kee
    • East Asian mathematical journal
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    • v.19 no.1
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    • pp.121-131
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    • 2003
  • We extend the characterization for the analytic Besov space obtained by Nowak to the invariant harmonic Besov space.

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Ultrasound Harmonic Imaging Method based on Harmonic Quadrature Demodulation (하모닉 직교 방식의 초음파 고조파 영상화 기법)

  • Kim, Sang-Min;Song, Jae-Hee;Song, Tai-Kyong
    • Journal of Biomedical Engineering Research
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    • v.30 no.1
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    • pp.79-88
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    • 2009
  • A harmonic quadrature demodulation method to extract the second harmonic component from focused ultrasound signals after a single transmit-receive event is proposed. In the proposed method, the focused ultrasound signal is converted into baseband inphase and quadrature components by multiplying with sine and cosine signals both having twice the center frequency of the transmitted signal and filtering the two modulated signals. The quadrature component is then passed through a Hilbert filter to be added to the inphase component, which leaves only the envelope of the second harmonic component. A novel phase estimation technique is employed in the proposed method to avoid the phase mismatch between the focused signal and the two modulating signals. The proposed method is verified through both theoretical analysis and computer simulations. It is shown that compared to the pulse inversion scheme the proposed method provides almost the same results for stationary targets and significantly improved harmonic to fundamental ratio for moving targets.

A Study on the Harmonic Current Characteristic and Emission Value Assess Method Considering the Linear Load (선형부하가 고려된 고조파 전류 특성 및 방출값 평가)

  • Park, Yong-Up;Choi, Seung-Hoon;Chang, Joon-Soo
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.59 no.1
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    • pp.33-39
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    • 2010
  • In order to operate the power system satisfactory for both system operators and customers, it is important to limit the harmonic currents to the allowable levels which injected into the system from the distorting installations. In this regard, the principles for the allocation of emission limits on individual customer were introduced in the technical report of IEC61000-3-6. According to these general principles, the emission limits are dependent on the agreed power of the customer, the power of the harmonic-generating equipment, and the system characteristics. The considerations in this report are very comprehensive and the process introduced is practical enough to implement as it is. However, there is a fact not appropriately dealing in the report that could be a very tickle but has a huge impact on determining the emission limit. This is the effect of non-harmonic load currents. More precisely, these are from the equipments which do not emit any harmonic or may emit harmonics but this specific order under the consideration by themselves if the source power is sinusoidal. The load currents originated from these equipments have an effect of active filter against the specific order of harmonic therefore, these should be dealt as a significant factoron the process of determining the emission limits for individual customer.

A Study on the Series and Parallel Resonant Filters for Harmonic Currents Reduction of Nonlinear Loads (비선형부하의 고조파전류 저감을 위한 직렬 및 병렬 동조필터에 관한 연구)

  • 김경철;강윤모;백승현;김종욱
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.17 no.6
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    • pp.113-118
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    • 2003
  • This paper characterizes typical nonlinear loads into two types of harmonic sources, i.e., harmonic voltage source and harmonic current source. A series resonant filter is very effective in harmonic reduction for harmonic voltage source type of nonlinear loads such as personal computer loads with smoothing dc capacitors. A parallel resonant filter is suited for current source type of nonlinear loads such as ac drives with smoothing dc reactors. General compensation characteristics and comparison of series and parallel resonant filters are given analytically and experimentally. Compliance with IEC Std 1000-3-2 has been evaluated for limiting harmonic distortion.

Analysis of Harmonic Currents Propagation on the Self-Excited Induction Generator with Nonlinear Loads

  • Nazir, Refdinal
    • Journal of Electrical Engineering and Technology
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    • v.9 no.6
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    • pp.1935-1943
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    • 2014
  • In recent years, the induction machines are increasingly being used as self-excited induction generators (SEIG). This generator is especially widely employed for small-scale power plants driven by renewable energy sources. The application of power electronic components in the induction generator control (IGC) and the loading of SEIG using nonlinear loads will generate harmonic currents. This paper analyzes the propogation of harmonic currents on the SEIG with nonlinear loads. Transfer function method in the frequency domain is used to calculate the gain and phase angle of each harmonic current component which are generated by a nonlinear loads. Through the superposition approach, this method has also been used to analyze the propagation of harmonic currents from nonlinear load to the stator windings. The simulation for the propagation of harmonic currents for a 4 pole, 1.5 kW, 50Hz, 3.5A, Y-connected, rotor-cage SEIG with energy-saving lamps, have provided results almost the same with the experiment. It can prove that the validity of the proposed models and methods. The study results showed that the propagation of harmonic currents on the stator windings rejects high order harmonics and attenuates low order harmonics, consequently THDI diminish significantly on the stator windings.

A Study on the 2nd Harmonic Blocking Scheme and Setting Value of a Current Differential Relay for 154 kV Transformers to Prevent Maloperation (154 kV 변압기 보호용 비율차동계전기 오동작 방지를 위한 2고조파 억제 방식의 적용방법 및 정정값에 관한 연구)

  • Son, Yong-Beom;Kang, Sang-Hee
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.67 no.1
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    • pp.29-37
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    • 2018
  • Inrush current and fault current in a transformer need to be distinguished from one another. In order to do this, KEPCO uses a 2nd harmonic restraint/block method. We use two setting values for 2nd harmonic restraint; 15% and 10%. We also apply per-phase blocking method among various harmonic restraint methods. If the transformer is located at the radial system, we adjust 10% in the 2nd harmonic restraint, but this method is not enough to prevent mal-operations of the current differential relay and let us spend more time to change setting value again as the power system changes. In this paper, a more reasonable setting value for a 2nd harmonic blocking scheme in KEPCO is proposed. To present a proposed method, the fault data of the current differential relays which have occurred since 2009 are analyzed. To evaluate the performance of the proposed method, the results of the RTDS test for the current differential relay of the transformer by KEPCO are analyzed.

A Study on the Real Features of Harmonic Obstacle (고조파 장해의 진상에 관한 연구)

  • 이해기
    • Journal of the Korean Society of Safety
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    • v.13 no.4
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    • pp.162-171
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    • 1998
  • This paper presents the harmonics obstacle analysis and countermeasure of electrical consumption a place. Harmonics that can be cosidered as a environmental pollution of the power systems become the cause of the accidents and damages. The responsibility of eliminating the harmonics firstly lies on the generating side. But the original characteristics of the system sush as the harmonic transfer characteristics and the impedance of the system affect each other in the process of the generation and transmission of the harmonic. Therefore it is very difficult to specify clearly the harmonic controlling responsibility, because electric machinery generating harmonics are various in the industrial fields. The output of a inverter has a high harmonic content. There are several ways of minimizing the output harmonic content. One way is to use pulse width modulation techniques within inverter. An alternative method is to combine a number of square-wave inverters. In this research, we measure the harmonic of the countermeasure of electrical consumption a place. The paper present the problem of new harmonic elimination method of PWM inverter fed induction motor system using W-FT series. In the future, the proposed PWM pattern by W-FT series is effective not only to the induction motor but also to the electromagnetic machine such as voltage reglator, UPS.

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