• Proceedings of the KIPE Conference
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• 2012.11a
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• pp.249-250
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• 2012

해상 풍력 발전은 가장 유망한 재생 에너지원의 하나이며, 육상 풍력 발전보다 풍력이 강력하고 일정하여 장시간 고출력 발생이 가능하다. 또한 소음, 공간적 한계, 경관훼손 등 기존 육상 풍력 발전의 단점을 보완하고 초대형 단지조성이 가능한 장점이 있다. 초대형 해상풍력단지에는 일반적으로 MW급의 해상풍력발전기가 사용된다. 본 논문에서는 MW급의 해상 풍력발전기에 ANPC(Active Neutral-Point-Clamped) Multi-Level VSC(Voltage Source Converter)를 적용하여 Back-to-Back으로 구성한 시스템을 제안하고 계통연계형 풍력 발전 시스템을 모의한 시뮬레이션을 통하여 제안된 시스템의 성능을 검증한다.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.4
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• pp.105-110
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• 1998

In this study, statistical and neural network methods were used to recognize the cutting tool states. This system employed the tool dynamometer and cutting force signals which are processed from the tool dynamometer sensor using linear discriminent function. To learn the necessary input/output mapping for turning operation diagnosis, the weights and thresholds of the neural network were adjusted according to the error back propagation method during off-line training. The cutting conditions, cutting force ratios and statistical values(standard deviation, coefficient of variation) attained from the cutting force signals were used as the inputs to the neural network. Through the suggested neural network a cutting tool states may be successfully diagnosed.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.50 no.3
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• pp.107-113
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• 2001

This paper deals with speed control of DC servo motor using a PID controller with a gain tuning based on a Back-Propagation(BP) Learning Algorithm. Conventionally a PID controller has been used in the industrial control. But a PID controller should produce suitable parameters for each system. Also, variables of the PID controller should be changed according to environments, disturbances and loads. In this paper described by a experiment that contained a method using a PID controller with a gain tuning based on a Back-Propagation(BP) Learning Algorithm, we developed speed characteristics of a DC servo motor on variable loads. The parameters of the controller are determined by neural network performed on on-line system after training the neural network on off-line system.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.2
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• pp.152-159
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• 2010

We propose a semi-analytical current conduction model for depletion-mode n-type nanowire field-effect transistors (NWFETs) with top-gate structure. The NWFET model is based on an equivalent circuit consisting of two back-to-back Schottky diodes for the metal-semiconductor (MS) contacts and the intrinsic top-gate NWFET. The intrinsic top-gate NWFET model is derived from the current conduction mechanisms due to bulk charges through the center neutral region as well as of accumulation charges through the surface accumulation region, based on the electrostatic method, and thus it includes all current conduction mechanisms of the NWFET operating at various top-gate bias conditions. Our previously developed Schottky diode model is used for the MS contacts. The newly developed model is integrated into ADS, in which the intrinsic part of the NWFET is developed by utilizing the Symbolically Defined Device (SDD) for an equation-based nonlinear model. The results simulated from the newly developed NWFET model reproduce considerably well the reported experimental results.

• Proceedings of the KIEE Conference
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• 1993.07a
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• pp.120-123
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• 1993

This paper presents the developing a new algorithm for detecting the Back fed Earth Fault in three wire-unigrounded distribution system by zero sequence admittance. So called "Backfed Earth Fault" of the electric power distribution line refers to a class of earth faults that the load-side line only is grounded, following after the distribution line broken into two parts, the source-side and the load-side. Because its mechanism differs from that of other earth faults, it is therefore, required to examine. This paper deals with the detailed software of the digital protective relay for Backfed earth fault. In order to prove that the proposed schemes is good, we performed off-line simulation using data from EMTP and ETSA(Electrcity Trust Of South Austrilia). It is shown that the suggested algorithm is never mal operated.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.5
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• pp.57-64
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• 2015

This paper proposes a new switching algorithm for an controllable clamp snubber to improve the efficiency of a fly-back converter system. This system uses an controllable clamp method for the snubber circuit for the efficiency and reliability of the system. However, the active clamp snubber circuit has the disadvantage that system efficiency is decreased by switch operating time because of heat loss in resonance between the snubber capacitor and leakage inductance. To address this, this paper proposes a new switching algorithm. The proposed algorithm is a technique to reduce power consumption by reducing the resonance of the snubber switch operation time. Also, the snubber switch is operated at zero voltage switching by turning on the snubber switch before main switch turn-off. Experimental results are presented to show the validity of the proposed controllable clamp control algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.1
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• pp.21-28
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• 2009

DFT-spread OFDM(Discrete Fourier Transform-Spread Orthogonal Frequency Division Multiplexing) is very effective for solving the PAPR(Peak-to-Average Power Ratio) problem. Therefore, the SC-FDMA(Single Carrier-Frequency Division Multiple Access) which is basically same to the DFT spread OFDM was adopted as the uplink standard of the 3GPP LTE ($3^{rd}$ Generation Partnership Project Long Term Evolution). Unlike the ordinary OFDM system, the SC-FDMA using DFT spreading method is vulnerable to the ICI(Inter-Carrier Interference) problem caused by the phase noise and IQ(In-phase/Quadrature) imbalance and effected FDE(Frequency Domain Equalizer). In this paper, the ICI effects from the phase noise and IQ imbalance which can be problems in uplink transmission are analyzed according the back-off level of HPA. Next, we propose the equalizer algorithm to remove the ICI effects. This proposed equalizer based on the FDE can be considered as up-graded and improved version of PNS(Phase Noise Suppression) algorithm. This proposed equalizer effectively compensates the ICI resulting from the phase noise and IQ imbalance. Finally, through the computer simulation, it can be shown that about SNR=14 dB is required for the $BER=10^{-4}$ after ICI compensation when the back-off is 4.5 dB, $\varepsilon=0.005$, $\phi=5^{\circ}$, and $pn=0.06\;rad^2$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10A
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• pp.1003-1013
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• 2006

There is a serious problem in an 802.11g VoWLAN (Voice over Wireless LAN) terminal that talk time is less than 30% compared with an 802.11b terminal. It is almost impossible to achieve talk time level of the 802.11b MAC transmission method because IEEE 802.11g uses OFDM modulation, which is a kind of multi-carrier method and OFDM transmission speed is 54 Mbps faster than normal modulation. In this paper, a new concept of a Holdover time as a power saving method during a call with 802.11g terminal is suggested for the first time. Increase in the number of engaged terminals as a result of holdover time causes to QoS problem because of the increase in the number of back-off and then contention window. In this paper, to solve the QoS problem, a new approach is suggested such that when in down lint the sequence number of 802.11 G.711 is analyzed in the MAC of the terminal and then the Hold over time depending on loss rate is changed. Also, consumption of an electric current of 802.11b/g and MAC parameter's performance due to busy traffic caused by increase in the number of terminal are analyzed and then real data using VQT and Airopeek are analyzed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.4
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• pp.484-489
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• 2014

Three phase PWM(Pulse Width Modulation) converter of the small-scale wind power system is able to charge battery under the rated wind speed regions. However, it is impossible to control output power of converter at the over win speed region because back-EMF(Electro Motive Force) of PMSG(Permanent Magnet Synchronous Generator) is higher than the battery terminal voltage of PMSG is reduced. However, the cut-off wind speed exists although battery charging algorithm is implemented by flux weakening control method. Therefore, this paper performs analysis of other factors which affects limitation wind speed. The validity of the analysis are verified through simulation.

• Journal of Korean Institute of Industrial Engineers
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• v.41 no.4
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• pp.330-337
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• 2015

A bucket-brigade is a way of transporting items where items are passed from one person to the next. The operation of the bucket brigade imitates the cooperative behavior of ants when brood, food or other resources are moved. Koo (2009) presented a bucket brigade-based assembly cell where each worker follows a simple rule: perform assembly operations on a product until the next worker downstream takes it over; then go back to the previous worker upstream to take over a new assembly job. In this way, the flow line is self-balanced without any predetermined job assignment. However, there are some productivity losses related to hand-off and blocking. This paper examines the hand-off and blocking losses and presents a new bucket brigade-based assembly cell where working areas for each assembler is restricted with the help of buffer interfaces. Simulation experiments are used to validate the performance of the new assembly system.