• Korean Journal of Optics and Photonics
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• v.31 no.5
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• pp.218-222
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• 2020

In this paper, we have experimentally demonstrated a 2-kW-class spectrally-beam-combined laser with high beam quality, using narrow-linewidth ytterbium-doped polarization-maintaining fiber amplifiers. Five fiber amplifiers with different center wavelengths were implemented for the spectrally-beam-combined laser. The center wavelengths of the five amplifiers were 1062, 1063, 1064, 1065, and 1066 nm, respectively. A phase-modulated laser diode was used as a seed source for each amplifier. The seed sources were modulated by filtered pseudorandom-bit-sequence (PRBS) signals 5 GHz in linewidth. The polarization-maintaining large-mode-area fiber with a core size of 30 ㎛ was used as a delivery fiber to mitigate the stimulated Brillouin scattering (SBS) effect. The laser beams from five amplifiers were spectrally combined by a multilayer dielectric diffraction grating. The maximum output power and beam quality M² of the combined laser were measured to be 2.3 kW and 1.74, respectively.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.3
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• pp.179-185
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• 2008

In this paper, an advanced torque control scheme of SRM using DITC(Direct Instantaneous Torque Control) and PWM(pulse width modulation) is presented. Different from conventional DITC method, proposed method uses one or two switching modes at every sampling time, instead of only one switching mode. The duty ratio of the phase switch is regulated according to the torque error and simple control rules of DITC. Moreover the sampling time of control can be extended, which allows implementation on low cost micro-controllers. A simple calculation of PWM can assure a constant switching frequency with an excellent control performance. The proposed control method is verified by the simulations and experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.431-438
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• 2012

Non-linear turbojet engine controller with high operational performance has been designed for the high maneuverability UAV. The turbojet engine dynamic performance code has been developed to reflect the non-linear characteristics on controller design, by which the necessity of non-linear controller design was justified by investigating the limitation of linear model derived from the dynamic performance. The PI-like fuzzy controller was designed and enhanced by combining with conventional derivative control. This designed fuzzy controller proves its effectiveness by showing superior control performances over the conventional PID controller along with guaranteeing the safe operation within compressor surge, flame out and turbine temperature limits etc.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.224-224
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• 2003

광통신을 위한 구성 요소는 빛을 발생시키는 발광소자, 빛을 검출하는 수광소자 그리고 광신호를 처리하는 광신호처리 소자로 구성된다. 이때 각 소자간 광전송과 광소자에 의한 광 신호 처리 과정에서 광전송 손실이 심각하게 일어나 광정보를 상실하게 되므로 각 요소별로 광신호 증폭이 반드시 필요하다. 뿐만 아니라 완전 광화에 의한 초고속/대용량 광통신망의 구축에는 저가이며, 광집적화가 가능한 광도파로형 광증폭기가 요구되고 있다. 짧은 거리에 높은 증폭 효율을 얻기 위한 광도파로형 광증폭기를 구현하기 위해서는 광통신 파장대인 1.55$\mu\textrm{m}$ 대역의 증폭이 가능한 Er 이온을 고농도로 도핑 할 필요가 있다. 그러나 Er 이온을 단순히 고농도로 첨가하면 Er-Er 간 뭉침 현상에 의해 더 이상의 증폭이 어렵게 된다. 본 연구에서는 이러한 문제를 해결하면서 스핀 코팅이 가능하여 저가 공정이 가능한 유/무기 졸-겔 재료 내에 Er 이온을 제어된 방법으로 첨가하고 그 결합 환경을 FT-IR 및 $^{17}$ O-NMR로 분석하였다. 유/무기 졸겔 재료 제조를 위하여 먼저 MPTS(MethAcryoxyPropylTrimethoxySilane)를 부분 가수분해한 후 ZrOCl$_2$.8$_2$O (Zirconyl Chloride Octahydrate) 와 ErCl$_3$. 6$H_2O$ (Erbium(III) Chloride Hexahydrate)를 순차적으로 결합시키고, Zr/MPTS 및 Zr/Er의 첨가비에 따른 발광 특성을 PL(photoluminescence) 스팩트럼으로 분석하여 Er 이온의 주위 결합 환경이 PL에 미치는 영향을 조사하였다. 또한 Si 기판에 코팅한 Er이 도핑된 유/무기 하이브리드 졸-겔 코팅막의 굴절율 등 광도파로 재료로서의 특성도 프리즘 커플러 등을 이용하여 조사하였다.

• Journal of KIISE:Databases
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• v.30 no.1
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• pp.80-94
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• 2003

In this paper. we propose an enhanced concurrency control algorithm that minimizes the query delay efficiently. The factors that delay search operations and deteriorate the concurrency of index structures are node splits and MBR updates in multi dimensional index structures. In our algorithm, to reduce the query delay by split operations, we optimize exclusive latching time on a split node. It holds exclusive latches not during whole split time but only during physical node split time that occupies small part of whole split time. Also to avoid the query delay by MBR updates we introduce partial lock coupling(PLC) technique. The PLC technique increases concurrency by using lock coupling only in case of MBR shrinking operations that are less frequent than MBR expansion operations. For performance evaluation, we implement the proposed algorithm and one of the existing link technique-based algorithms on MIDAS-III that is a storage system of a BADA-III DBMS. We show through various experiments that our proposed algorithm outperforms the existing algorithm In terms of throughput and response time.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.37 no.5
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• pp.19-28
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• 2000

It is not so easy to control the wheeled mobile robot because of some causes like non-holonomic constraints. To overcome these problems, a controller that PD system is combined with fuzzy process is composed of several steps that have each separate algorithm and niche search algorithm and immune algorithm is applied partly. Output term set is changed by search that is performed to get optimal elements and then the rule base is also reformed. The fitness for the altered system is estimated and the surplus elements are removed. After the adjustment of output term set and rule base is finished, input and output membership functions is tuned.

• Proceedings of the KIPE Conference
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• 2013.11a
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• pp.131-132
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• 2013

BESS를 대용량화 하기 위하여 병렬운전에 관련하여 많은 연구가 진행 중이다. 병렬운전 알고리즘의 제어 목표는 인버터 간의 순환전류를 제거하고, 부하 분담이 균등하게 하는 것에 있다. 이를 위하여 연구되었던 방법 중 전압 제어와 전류 제어의 인버터를 결합한 Master-Slave 방식은 통신을 통하여 정확한 부하분담이 가능하지만 통신지연 발생시 과도상태에 과전류가 발생 할 수 있다는 단점을 갖는다. 본 논문은 독립된 계통에서 BESS가 병렬운전 중 스텝부하 투입시 통신지연 시간 동안의 과도상태에서 과전류가 발생하지 않도록 하는 Droop Control를 적용한 제어 알고리즘을 제안한다.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.6
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• pp.946-961
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• 2004

A new adaptive controller which combines a model reference adaptive controller (MRAC) and a fuzzy controller is developed for unstable nonlinear time-invariant systems. The fuzzy controller is used to analyze and to compensate the nonlinear time-invariant characteristics of the plant. The MRAC is applied to control the linear time-invariant subsystem of the unknown plant, where the nonlinear time-invariant plant is supposed to comprise a nonlinear time-invariant subsystem and a linear time-invariant subsystem. The stability analysis for the overall system is discussed in view of global asymptotic stability. In conclusion. the unknown nonlinear time-invariant plant can be controlled by the new adaptive control theory such that the output error of the given plant converges to zero asymptotically.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2001.12a
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• pp.149-152
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• 2001

본 논문은 연속 시간과 이산 시간에서의 스위칭 모드 퍼지 모델 기반 제어기의 새로운 설계 기법에 대해서 논의한다. 스위칭 모드 퍼지 모델 기반 제어기의 설계에는 Takagi-Sugeno(75) 퍼지 시스템이 사용된다. 이 스위칭 모드 퍼지 모델 기반 제어기는 "정복-분할(divide and conquer)"이라는 하향식 접근 방식을 이용한다. 이 방법은 여러 개의 규칙을 가지고 있는 시스템에서 유한의 하위 시스템으로 시스템을 분할하여 각각의 부분 해를 구하고 이들을 결합하여 전체 시스템의 해를 구하는 방법이다. 제어기의 설계 조건은 주어진 75 퍼지 시스템의 안정화를 보장하는 선형 행렬 부등식들(LMls)에 의해 결정된다. 적절한 시뮬레이션 예제를 통한 성능 비교를 통해 본 논문의 우수성을 입증한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.2
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• pp.397-402
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• 1999

In this paper, we derive dynamic equation of a simulated helicopter and propose the control method base on a neural network to control its attitude. The coupling coefficients are adjusted to minimize the error between the output of a control system and the reference value. The gain of the proposed controller are automatically adjusted by the back propagation of a neural network. Simulation results using MATLAB are given in this paper.