• Title/Summary/Keyword: Zero region

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Photonic Quasi-crystal Fiber for Orbital Angular Momentum Modes with Ultra-flat Dispersion

  • Kim, Myunghwan;Kim, Soeun
    • Current Optics and Photonics
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    • v.3 no.4
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    • pp.298-303
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    • 2019
  • We propose a photonic quasi-crystal fiber (PQF) for supporting up to 14 orbital angular momentum (OAM) modes with low and ultra-flat dispersion characteristics over the C+L bands. The designed PQF which consists of a large hollow center and quasi structural small air holes in the clad region exhibits low confinement losses and a large effective index separation (>$10^{-4}$) between the vector modes. This proposed fiber could potentially be exploited for mode division multiplexing and other OAM mode applications in fibers.

INEQUALITIES CONCERNING POLYNOMIAL AND ITS DERIVATIVE

  • Zargar, B.A.;Gulzar, M.H.;Akhter, Tawheeda
    • Korean Journal of Mathematics
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    • v.29 no.3
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    • pp.631-638
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    • 2021
  • In this paper, some sharp inequalities for ordinary derivative P'(z) and polar derivative DαP(z) = nP(z) + (α - z)P'(z) are obtained by including some of the coefficients and modulus of each individual zero of a polynomial P(z) of degree n not vanishing in the region |z| > k, k ≥ 1. Our results also improve the bounds of Turán's and Aziz's inequalities.

Compensation of the rotor time constant of induction motor using current error feedback (전류오차 궤환을 이용한 유도전동기 회전자 시정수 보상)

  • 김승민;이무영;권우현
    • 제어로봇시스템학회:학술대회논문집
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    • 1997.10a
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    • pp.195-198
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    • 1997
  • This paper proposes the effective compensation method of the rotor time constant of induction motor. An indirect vector control method is highly dependent on the motor parameters. To solve the problem of performance degradation due to parameter variation in an indirect vector control of induction motor, we compensate the rotor time constant by current error feedback. The proposed method is a simple on-line rotor time constant compensation method using the information from terminal voltages and currents. As the current error, difference between current command and estimated current, approaches to zero, the value of rotor time constant in an indirect vector controller follows the real value of induction motor. This scheme is valid transient region as well as steady state region regardless of low or high speed. This method is verified by computer simulation. For this, we constructed the simulation model of induction motor, indirect vector controller and current regulated PWM (CRPWM) voltage source inverter (VSI) using SIMULINK in MATLAB.

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A New Overmodulation Method to Extend Linearity Region of a PWM Inverter (PWM 인버터에서 선형영역 확장을 위한 새로운 과변조 기법)

  • Kim, Sang-Hoon;Han, Dae-Woong
    • Journal of Industrial Technology
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    • v.21 no.B
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    • pp.59-66
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    • 2001
  • In this paper, a novel overmodulation strategy for PWM inverters to extend linearity region is presented. The proposed strategy uses the concept of space-vector PWM(SVPWM) based on the zero sequence signal(offset voltage) injection principle. So, by modifying the pole voltage simply, the linear control of inverter output voltage over the whole overmodulation range can be achieved easily. The proposed strategy is so simple that its practical implementation is easy. The validity of the proposed strategy is confirmed by the experimental results.

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A Study of Internal QMSA for Mobile Communication (이동통신용 내장형 QMSA에 대한 연구)

  • Ryu, Hyun;Lee, Nam-Yul;Park, Sung-Kyo;Park, Chong-Baek
    • Proceedings of the IEEK Conference
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    • 1998.10a
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    • pp.35-38
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    • 1998
  • In this paper we fabricated QMSAs for 850MHz band on the teflon substrate with $\varepsilon_1-2.6, $ $t=1.6mm(\pm0.08)(CGP-500).$ We measured the resonant frequency and the return loss with cutting the gap region between radiation patch and ground plate by a 5mm length step by step. As a result we found that the measured data was not so bad unlike other papers when the gap region was closer to zero, especially under 10mm.

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Tracking Control for Biped Robot (이족 보행 로봇을 위한 추적 제어)

  • 이용권;박종현
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.10a
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    • pp.315-318
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    • 1995
  • In this paper, an optimal trunk trajectory for stable walking of biped robots is expressed as a simple differential equation, which is then solved by numerical methods. We used ZMP (Zero Moment Point), the virtual total ground reaction point within the region of the supporting food, as the criterion of stability of biped robot walking. If the ZMP is located outside of the stable region in dynamic walking, biped robots fall down. The biped robot considered in this paper consists of two legs and a trunk. The trajectories of the two legs and the ZMP of the biped robot are determined such that they are similar ti those of a human. Based upon those trajectories, the trunk trajectory is solved by numerically integrating differential dynamic equations. Leg motions are controlled by the computed torque control method. The effectiveness of control algorithm as well as the trajectories is confirmed by computer simulations.

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Sensorless control of the Next Generation High Speed Drive System in low speed region (차세대 고속전철 저속영역에서의 센서리스 제어)

  • Jin, Kang-Hwan;Suh, Yong-Hun;Lee, Sang-Hyun;Kim, Yoon-Ho
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.25 no.12
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    • pp.82-87
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    • 2011
  • In this paper, a sensorless speed control system is designed for the next generation high speed railway at zero and low speed region. The applied vector control scheme is a maximum torque per ampere(MTPA) method to utilize reluctance torque of IPMSM. The designed sensorless control scheme is a rotating high frequency voltage signal injection method. To verify the designed system, a simulator for the vector controller and sensorless controller is implemented using Matlab/simulink.

A Study on Large Area Black Silicon Solar Cell Using Radio-Frequency Multi-Hollow cathode Plasma System (Radio Frequency Multi-Hollow Cathode 플라즈마 시스템을 이용한 대면적 블랙 실리콘 태양전지에 관한 연구)

  • 유진수;임동건;양계준;이준신
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.52 no.11
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    • pp.496-500
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    • 2003
  • A low-cost, large area, random, maskless texturing scheme independent of crystal orientation is expected to significantly impact terrestrial photovoltaic technology. We investigated silicon surface microstructures formed by reactive ion etching (RIE) in Multi-Hollow cathode system. Desirable texturing effect has been achieved when radio-frequency (rf) power of about 20 Watt per one hollow cathode glow is applied for our RF Multi-Hollow cathode system. The black silicon etched surface shows almost zero reflectance in the visible region as well as in near IR region. The etched silicon surface is covered by columnar microstructures with diameters from 50 to 100 nm and depth of about 500 nm. We have successfully achieved 11.7% efficiency of mono-crystalline silicon solar cell and 10.2% multi-crystalline silicon solar cell.

Sensorless Speed Control of Induction Motor in Wide Speed Range (속도검출기가 없는 유도전동기의 광범위 속도 제어)

  • Ryu, Hyung-Min;Ha, Jung-Ik;Sul, Seung-Ki
    • Proceedings of the KIEE Conference
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    • 1999.07f
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    • pp.2487-2489
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    • 1999
  • This paper proposes a wide speed range sensorless vector control strategy. At low speed region, the difference of high frequency impedances is used in order to estimate the rotor flux angle. At high speed region this algorithm is combined with the adaptive observer. It enables the stable operation even at zero speed under the rated load condition This is verified by experimental results.

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New degradation mechanism of GaAs HBT induced by Hot carriers (핫 캐리어에 의한 GaAs HBT의 새로운 열화 메카니즘)

  • 권재훈;김도현;송정근
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.34D no.11
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    • pp.30-36
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    • 1997
  • AlGaAs/GaAs HBTs are developed well enough to be commercialized as an active device in optical transmission system, but there remains the unanswered questions about reliability. In this paper we applied the reverse constant current stress at the high voltage in avalanche region for a long time to find out a new degradation mechanism of junctrion I-V. The unction off-set voltage at which the current vanishes to zero was shifted to the negative direction of applied bias due to the increment of leakage current as the stress time increases. It was identified that the degradation was induced by the hot carriers which were generated at space charge region and trapped at the interface between GaAs base and the passivation nitride enhancing the electric field across the nesa edge.

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