• Title/Summary/Keyword: Zero region

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Advanced Static Over-modulation Scheme using Offset Voltages Injection for Simple Implementation and Less Harmonics

  • Lee, Dong-Myung
    • Journal of Electrical Engineering and Technology
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    • v.10 no.1
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    • pp.138-145
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    • 2015
  • In this paper, a novel static overmodulation scheme (OVM) for space-vector PWM (SVPWM) is proposed. The proposed static OVM scheme uses the concept of adding offset voltages in linear region as well as overmodulation region to fully utilize DC-link voltage. By employing zero sequence voltage injection, the proposed scheme reduces procedures for achieving SVPWM such as complicated gating time calculation. In addition, this paper proposes a stepwise discontinuous angle movement in high modulation region in order to reduce Total Harmonic Distortion (THD). The validity of the proposed scheme is verified through theoretical analysis and experimental results.

Turbulent flow in annuli depending on the position of roughness (거칠기 위치에 따른 이중관 내의 난류유동)

  • An, Su-Hwan;Kim, Gyeong-Cheon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.7
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    • pp.891-899
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    • 1997
  • This paper presents the results of a detailed experimental examination of fully developed asymmetric flows between annular tubes with square-ribbed surface roughness. The main emphasis of the research has been on establishing the turbulence structure, particularly in the central region of the channel where the two dissimilar wall flows interact. Measurements have included profiles of time mean velocities, turbulence intensities, turbulent shear stresses, triple velocity correlations, skewness, and flatness. The region of greatest interaction is characterized by strong diffusional transport of turbulent shear stress and kinetic energy from rough toward the smooth wall region, giving rise to an appreciable separation between the planes of zero shear stresses depending on positions of roughness on the walls.

Satellite Attitude Control on Reaction Wheel Low-Speed Region (반작용휠 저속구간에서의 위성자세제어)

  • Son, Jun-Won;Park, Young-Woong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.11
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    • pp.967-974
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    • 2017
  • Reaction wheel shows nonlinear torque response on low-speed region due to friction. Thus precise satellite attitude control on this region is hard to achieve. Previous research tries to solve this problem, by compensating friction or applying dither command. However, due to difficulties of drag torque modeling or frequent zero wheel speed crossing, these methods are not suitable to apply on the real satellite attitude control. To solve this problem, we propose the attitude controller gain adjustment method based on the attitude error.

A Stable Sensorless Speed Control for Induction Motor in the Overall Range (전영역에서 안정된 유도전동기의 센서리스 속도제어)

  • 김종수;김성환;오세진
    • Journal of Advanced Marine Engineering and Technology
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    • v.28 no.4
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    • pp.641-647
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    • 2004
  • By most sensorless speed control schemes for induction motor. the control performances in high speed range are good, but it is difficult to obtain satisfactory results in low speed region. This paper proposes a new method controlling the low and the high speed regions separately to attain the stable operation in the overall range. The current error compensation method, in which the controlled stator voltage is applied to the induction motor so that the error between stator currents of the numerical model and the actual motor can be forced to decay to zero as time proceeds. is used in the low speed region In the high speed region. the method with adaptive observer is utilized. This control strategy contains an adaptive state observer for flux estimation. The rotor speed can be calculated from the rotor flux and the motor currents. The experimental results indicate good speed and load responses from the very low speed range to the high, and also show accurate speed changing performance between the low and the high speed range.

Performance Analysis on the Initial Alignment of Laser Inertial Navigation System (레이저 관성항법장치 초기정렬 성능 분석)

  • Kim, Hyun-Seok;Kim, Cheon-Joong;Lee, Tae-Gyoo
    • Journal of the Korea Institute of Military Science and Technology
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    • v.12 no.5
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    • pp.622-635
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    • 2009
  • Laser Inertial Navigation System(LINS) consists of Ring Laser Gyroscopes(RLG) and accelerometers. RLG has a lock-in region in which there is zero output for input angular rates less than about 0.1deg/sec. The lock-in region is generated by the imperfect mirrors in RLG. To avoid the lock-in region, a sinusoidal motion called dither motion is applied on RLG. Therefore this dither motion is measured by RLG/accelerometer even if at a stop state. In this situation, the performance on the initial alignment of LINS can be degraded. In this paper, we analyze the performance on the initial alignment of LINS theoretically and experimentally. Analysis results include how dither motion, the pre-filter and the corner frequency in alignment loop affects the performance on the initial alignment of LINS.

A New Low Loss Quasi Parallel Resonant DC-Link Inverter with Variable Lossless Zero Voltage Duration (무손실 가변 영전압 구간을 갖는 새로운 저손실 준 병렬공진 직류-링크 인버터)

  • 권경안;김권호;최익;정용채;박민용
    • The Transactions of the Korean Institute of Power Electronics
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    • v.2 no.2
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    • pp.8-18
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    • 1997
  • In this paper, a New Low Loss Quasi-Parallel Resonant DC-Link(NLQPRDCL) Inverter which shows highly improved PWM capability, low loss characteristic and low voltage stress is presented. A method to minimize freewheeling interval, which is able to largely decrease DC-link operation losses and to steadily guarantee soft switching in the wide operation region is also proposed. In addition, lossless control of zero voltage duration of DC-link makes the proposed inverter maintain the advanced PWM capability even under a very low modulation index. Experiment and simulation were performed to verify validity of the proposed inverter topology.

Special quality research about action output waveform change by gap (1.0mm and 1.6mm) difference of $CO_2$ laser for skin disease (피부질환을 위한 $CO_2$ 레이저의 공극 (1.0mm 및 1.6mm)차이에 따른 동작출력 파형변화에 관한 특성연구)

  • Kim, Whi-Young
    • Proceedings of the KIEE Conference
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    • 2007.04c
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    • pp.156-158
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    • 2007
  • Laser wave length can have evaporation effect by absorption because outer skin or tissue of focus is consisted of water almost though absorption of water occurs more than 90% almost in formation thickness of very thin floor Can operate outer skin, steam by floor and correct incision of formation is available. Suture surgical operation is avaliable to vein or lymph system and surgical operation region can dry and see as eye and radish bleeding surgical operation is avaliable Specially, stability of tube both end output about pulse by weight very, this research can cause various curative effect because can reduce bulk and control easily current wave style of medical laser using electric power conversion device of high frequency way. If introduce ZVS (Zero Voltage Switching) or ZVZCS (Zero Voltage and Zero Current Switching), is more profitable because can reduce switching damage Because electric power department of proposed medical laser can do stable soft-switching in wide subordinate extent introducing ZVZCS technique by the first help and control department composes microcontroller, output current waveform user have free form make. Result that experiment because design and manufacture, brought result that improve of 20% than existing equipment, and will be bought to get into superior result if supplement as systematic late.

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An empirical bracketed duration relation for stable continental regions of North America

  • Lee, Jongwon;Green, Russell A.
    • Earthquakes and Structures
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    • v.3 no.1
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    • pp.1-15
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    • 2012
  • An empirical predictive relationship correlating bracketed duration to earthquake magnitude, site-to-source distance, and local site conditions (i.e. rock vs. stiff soil) for stable continental regions of North America is presented herein. The correlation was developed from data from 620 horizontal motions for central and eastern North America (CENA), consisting of 28 recorded motions and 592 scaled motions. The bracketed duration data was comprised of nonzero and zero durations. The non-linear mixed-effects regression technique was used to fit a predictive model to the nonzero duration data. To account for the zero duration data, logistic regression was conducted to model the probability of zero duration occurrences. Then, the probability models were applied as weighting functions to the NLME regression results. Comparing the bracketed durations for CENA motions with those from active shallow crustal regions (e.g. western North America: WNA), the motions in CENA have longer bracketed durations than those in the WNA. Especially for larger magnitudes at far distances, the bracketed durations in CENA tend to be significantly longer than those in WNA.

Special quality research about action output waveform change by gap (1.0mm and 1.6mm) difference of $CO_2$ laser for skin disease (피부질환을 위한 $CO_2$ 레이저의 공극차이에 따른 동작출력 변화에 관한 연구)

  • Kim, Whi-Young
    • Proceedings of the KIEE Conference
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    • 2007.04a
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    • pp.52-54
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    • 2007
  • Laser wave length can have evaporation effect by absorption because outer skin or tissue of focus is consisted of water almost though absorption of water occurs more than 90% almost in formation thickness of very thin floor. Can operate outer skin, steam by floor and correct incision of formation is available. Suture surgical operation is available to vein or lymph system and surgical operation region can dry and see as eye and radish bleeding surgical operation is available. Specially, stability of tube both end output about pulse by weight very, this research can cause various curative effect because can reduce bulk and control easily current wave style of medical laser using electric power conversion device of high frequency way. If introduce ZVS (Zero Voltage Switching) or ZVZCS (Zero Voltage and Zero Current Switching), is more profitable because can reduce switching damage. Because electric power department of proposed medical laser can do stable soft-switching in wide subordinate extent introducing ZVZCS technique by the first help and control department composes microcontroller, output current waveform user have free form make. Result that experiment because design and manufacture, brought result that improve of 20% than existing equipment, and will be bought to get into superior result if supplement as systematic late.

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A Random Access Scheme Robust to Timing Offsets for Uplink OFDMA Systems (타이밍오차에 강건한 상향링크 OFDMA 시스템의 랜덤 액세스 기법)

  • Song, Hyun-Joo;Rim, Dae-Woon;Jeong, Byung-Jang;Noh, Tae-Gyun;Rim, Min-Joong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.33 no.6A
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    • pp.659-665
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    • 2008
  • If ranging processes are not frequent in an uplink OFDMA system, the timing synchronization between base and mobile stations may not be maintained. Especially in the case of infrequent random accesses in a large cell, timing offsets can be considerable and the destroyed orthogonality of OFDMA signals may result in the degraded performance. This paper proposes a novel random access scheme for uplink OFDMA systems, which support the orthogonality of OFDMA signals with timing offsets by allowing a random access OFDMA symbol shorter than a normal one. In order to make uplink OFDMA systems robust to timing offsets, the proposed scheme inserts a zero-padding region in an OFDMA symbol.