• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.583-587
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• 2003

In this paper, the optimal performance of optical second-order polarization mode dispersion (PMD) compensation has been investigated theoretically in terms of minimization of the root-mean-square (RMS) pulse broadening. The optimal compensation vector in feedforward-type second-order PMD compensation has been derived, and the RMS pulse broadening factor after the optimal second-order PMD compensation has been analytically calculated. The calculated result has been compared with the previously reported simulation result where numerically optimized feedback scheme was adopted. They are in good agreement, which verifies the validity of the derivation. The investigation in this work will form the basis for the implementation of the feed-forward-type second-order PMD compensation.

• Journal of Power Electronics
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• v.19 no.4
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• pp.907-921
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• 2019

This paper presents two advanced hybrid pulse-width modulation (PWM) strategies for multilevel inverters (MLIs) that provide both common-mode voltage (CMV) elimination and current ripple reduction. The first PWM utilizes sequences that apply one switching state at the double ends of a half-carrier cycle. The second PWM combines the advantages of the former and an existing four-state PWM. Analyses of the harmonic characteristics of the two groups of switching sequences based on a general switching voltage model are carried out, and algorithms to optimize the current ripple are proposed. These methods are simple and can be implemented online for general n-level inverters. Using a three-level NPC inverter and a five-level CHB inverter, good performances in terms of the root mean square current ripple are obtained with the proposed PWM schemes as indicated through improved harmonic distortion factors when compared to existing schemes in almost the entire region of the modulation index. This also leads to a significant reduction in the current total harmonic distortion. Simulation and experimental results are provided to verify the effectiveness of the proposed PWM methods.

• Electrical & Electronic Materials
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• v.10 no.5
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• pp.434-439
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• 1997

It this paper, the piezoelectric and electro-induced strain properties of (P $b_{1-}$2x/3/B $i_{x}$ )[N $i_{1}$3/N $b_{2}$3/)$_{0.4}$( $Ti_{0.6}$Z $r_{0.4}$)$_{0.6}$] $O_3$ceramics (x=0, 0.005, 0.02) were investigated with the substitution of B $i^{3+}$, and the feasibility of the application for bimorph actuator was evaluated by measuring the dynamic properties of the piezoelectric bimorph fabricated with above ceramics. Dielectric constant was enhanced with the increase of B $i^{3+}$ substitution, and appeared the maximum value of 5032 at x=0.01 composition. Increasing the substitution of B $i^{3+}$, the electromechanical coefficient( $k_{p}$ , $k_{31}$ ) was increased up to the substitution of 0.5 mol% B $i^{3+}$, showed the value of 0.656, 0.439, respectively. The piezoelectric constant( $d_{33}$ $d_{31}$ ) had the highest value of 344, 825 with the substitution of 0.5 mol% B $i^{3+}$. The strain, generated by 60 Hz AC electric field, had the largest value of 1200($\times$10$^{-6}$ $\Delta$1/1) in the composition with the substitution of 0.5 mol% B $i^{3+}$. The dynamic properties of the bimorph actuator, fabricated with the composition substitution of 0.5 mol% B $i^{3+}$, showed the largest value of 325 $\mu$m at $\pm$150 V square pulse. square pulse.are pulse..

• Journal of Digital Convergence
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• v.10 no.5
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• pp.233-238
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• 2012

In a speech coding system using excitation source of voiced and unvoiced, it would be a distortion of speech waveform in case of exist a voiced and an unvoiced consonants in a frame. To solve this problem, this paper present a method of LMS-MPC uses individual pitch and LMS(Least Mean Square). I evaluate the MPC and LMS-MPC using LMS. As a result, SNRseg of LMS-MPC was improved 1.5dB for female voice and 1.3dB for male voice respectively. Compared to the MPC, SNRseg of LMS-MPC has been improved that I was able to control the distortion of the speech waveform finally. And so, I expect to be able to this method for cellular phone and smart phone using excitation source of low bit rate.

• Journal of Astronomy and Space Sciences
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• v.18 no.2
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• pp.137-144
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• 2001

This paper presents the REA thrusters performance estimation results for the KOREASAT F1&F2 launched in 1995 The satellite tracking data obtained from the ground system from end of 1999 to beginning of the 2000 are used to estimate the thruster performance. The estimation algorithm is derived from the least square estimation theory and designed to estimate the velocity change induced by the on-boarded thruster firing as well as the orbit parameter. The estimation results show that the Koreasat F1 thruster are in bad thruster condition of 64% performance for REA when it fires in on-pulse mode. Here, the performance is defined by the ratio of the resulted velocity change to that of planned. But, in the case o( the Koreasat F2, it is found that the performance approximately reaches up to 100%, even after the 5 years of the mission.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.49 no.8
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• pp.451-458
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• 2000

The precise speed and position control technique for Brushless DC Motor demands accurate position and speed feedback information. Generally, resolver or absolute encoders are used as speed and positiion sensor. But they increase cost and more problem happens at low speed than high speed specially. Therefore, in this paper, optimal speed observer is proposed for decreasing size and cost of whole system. And also, we consider the error problem about the system modeling and measurement at low speed range as well as high speed. The overall system consists of two parts, a drive and a speed observer. We make use of Least square curve fitting algorithm as speed observer and can overcome low resolution by proposed observer. Also, because of using the signal of hall sensor, robust control is possible in low speed as well as high speed for the change of the parameters of the system and disturbance. To construct observer using the signal of hall sensor, we design the pulse multiplier circuit and the software of microprocessor, AT89CC2051. Finally, the performance of the proposed observer is exemplified by some simulations and experiments.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.2083-2085
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• 2000

우리나라의 전열추진기술 프로그램에 따라 8�V의$\square$ $\square kJ$ 커패시터 뱅크 모듈이 제작되고 있다. 한 �V의 모듈은 6개의 22kV, 50kJ 자체 고장복구 커패시터와 주 스위치로서 각 모듈에 하나씩의 RVU-43 스위치를 사용하였다. 또 각 모듈에는 요구되는 전류 파형의 폭을 얻기 위하여 $20\sim160\;\mu\;H$의 펄스 파워 인덕터를 사용하였고 3개의 병렬 크로우바 스택을 적용하였다. 여러 종류의 스위치가 검토되었으며 그 중에서 펄스 파워 싸이리스터보다 가격이 싸면서 전류영점에서 차단기능이 있는 RVU-43 스위치가 선정되었다. 선정된 스위치(정격 25kV, 200kA, 120 Coulomb)에 대하여 자기방전 전압, 최소 동작전압, 동작 지연시간, 역전류 차단성능, 스위치 손실에 관한 특성시험을 행하고 그 결과를 보고한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.6
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• pp.34-40
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• 2009

The present study describes the methods and standards for the combustion stability assessment of a thrust chamber and a gas generator as parts of a liquid rocket engine. The first method uses a statistical approach through typical static combustion tests and the second one a dynamic assessment identifying decaying characteristics of pressure fluctuations excited by a pulse generating device. Based on accumulated test results, it is concluded that the maximal values for combustion stability are 3% of a chamber static pressure with a Root-Mean-Square value of pressure fluctuations, and 10 msec with a decay time.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.346-350
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• 2002

A glassy carbon electrode (GCE) modified with 2,2':6':2”-terpyridine (2,2':6':2”-TPR) using a spin coating method was applied for the highly selective and sensitive analysis of a trace amount of $Hg_2^{2+}$ ions. Various experimental parameters, which influenced the response of the 2,2':6':2”-TPR modified electrode to $Hg_2^{2+}$ ions, were optimized. The linear sweep and differential pulse voltammograms for the 2,2':6':2”-TPR modified electrode deposited with Hg show a well-defined anodic peak at +0.65 V (vs. Ag|AgCl). After a 25 min preconcentration time in an $Hg_2^{2+}$ ion solution (0.1 M acetate buffer, pH 5.0), differential pulse voltammetry(DPV) with 2,2':6':2”-TPR modified electrode shows a linear response between $1.0\;{\times}\;10^{-6}M\;and\;2.0\;{\times}\;10^{-7}M$. The least-square treatment of these data produce an equation of I[${\mu}A$] = 0.031 + 0.005C with r = 0.980(n = 5). The detection limit of this electrode with linear sweep voltammetry and differential pulse anodic voltammetry were $2.0\;{\times}\;10^{-6}M\;and\;8.0\;{\times}\;10^{-8}M$, respectively. The presence of Pb, Fe, Cd, Ti, Ni, Co, Mg, Al, Mn, and Zn did not interfere in the analysis of the $Hg_2^{2+}$ ion. The 2,2':6':2”-TPR modified GCE has been successfully applied in determination trace amounts of Hg in a human urine sample.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.145-156
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• 1990

In this study, thermophysical properties of the engineering ceramic materials such as $Al_{2}$O$_{3}$, Si$_{3}$N$_{4}$ and SiC were measured b y a single rectangular pulse heating method. The values of thermal diffusivities, specific heats, and thermal conductivities were measured as a function of temperature ranging form room temperature to 1300K. The measured thermal properties of one group of ceramic material were compared with those of other group and discussed in detail in connection with the chemical composition. Thus, some criteria for thermal design with the engineering ceramic materials were proposed.