• 대한기계학회논문집
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• 제17권1호
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• pp.38-45
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• 1993

본 연구에서는 선반작업에서의 피삭체의 형상을 특징형상(feature)단위로 정 의하였고, 이 특징형상을 이용하여 형상정의를 수행한 후 가공순서 및 가공조건을 대 화형식으로 입력하면 공구위치 데이터(CL data)를 자동으로 산출하고 이를 기계제어데 이터(MC data)로 변화시켜 주는 NC선반가공 프로그래밍시스템 FeaTURN (Feature-based TURNing system)을 개발하였다.

• 전력전자학회논문지
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• 제22권4호
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• pp.305-311
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• 2017

In this paper, the LLC resonant converter battery charger, using adaptive turn ratio scheme, is proposed to achieve high efficiency and wide range output voltage. The LLC converter high frequency transformer has an adaptively changed turn ratio by the auxiliary control circuitry. As a result, the optimal converter design with a large magnetizing inductance is easily achieved to minimize the conduction and the turn-off losses while providing widely regulated voltage gain capability to properly charge the Li-ion battery. The proposed converter operational principle and the optimal design considerations are illustrated in detail. Finally, several simulation results verify the proposed LLC resonant converter's effectiveness.

• 전기학회논문지
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• 제60권3호
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• pp.524-530
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• 2011

This paper analyzes fault tolerance under a stator turn fault, according to the winding configuration. Improvement of torque characteristics and fault tolerance can be achieved by winding configuration without additional methods. And, torque characteristics and fault tolerance according to the winding configuration can be usually analyzed by analytical method. But, when the stator turn fault generates, compare to the steady-state, analysis of torque characteristics and fault tolerance using the analytical method is not accurate because it does not reflect influence in mutual inductance and magnetic non-linearity. Therefore, analysis of torque characteristics and fault tolerance has to be performed by using the numerical method under fault condition. This paper develops fault characteristics according to the winding configuration using the FEM-base model considered magnetic non-linearity. And, this paper suggests fault tolerance improvement according to the winding configuration, by the comparison of 8/12 and 10/12 models, under fault condition.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.124-132
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• 2018

This paper proposes an LLC resonant converter based battery charger which utilizes an adaptive turn ratio scheme to achieve a wide output voltage range and high efficiency. The high frequency transformer of the LLC converter of the proposed strategy has an adaptively changed turn ratio through the auxiliary control circuit. As a result, an optimized converter design with high magnetizing inductance is possible, while minimizing conduction and turn-off losses and providing a regulated voltage gain to properly charge the lithium ion battery. For a step-by-step explanation, operational principle and optimal design considerations of the proposed converter are illustrated in detail. Finally, the effectiveness of the proposed strategy is verified through various experimental results and efficiency analysis based on prototype 300W Li-ion battery charger and battery pack.

• 대한전기학회논문지
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• 제45권4호
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• pp.562-567
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• 1996

A new lateral MOS controlled thyristor, named Shorted Anode LMCT(SA-LMCT), is proposed and analyzed by a two-dimensional device simulation. The device structure employs the implanted n+ layer which shorts the p+ anode together by a common metal electrode and provides a electron conduction path during turn-off period. The turn-off is achieved by not only diverting the hole current through the p+ cathode short but also providing the electron conduction path from the n-base into the n+ anode electrode. In addition, the modified shorted anode LMCT, which has an n+ short junction located inside the p+ anode junction, is also presented. It is shown that the modified SA-LMCT enjoys the advantage of no snap-back behavior in the forward characteristics with little sacrificing of the forward voltage drop. The simulation result shows that the turn-off times of SA-LMCT can be reduced by one-forth and the maximum controllable current density may be increased by 45 times at the expense of 0.34 V forward voltage drop as compared with conventional LMCT. (author). 11 refs., 6 figs., 1 tab.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.346-349
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• 1996

In application of high power IGBT PWM inverters, the treatable power range is considerably limited due to the overvoltage caused by the stray inductance components within the power circuit. This paper proposes a new gate drive circuit for IGBTs which can actively suppress the overvoltage across the driven IGBT at turn-off and the overvoltage across the opposite IGBT at turn-on while preserving the most simple and reliable power circuit. The turn-off driving scheme has adaptive feature to the amplitude of collector current, so that the overvoltage is limited much effectively at the larger collector current. The turn-on scheme is to decrease the rising rate of the collector current by increasing input capacitance during turn-on transient when the gate-emitter voltage is greater than threshold voltage. The experimental results under various normal and fault conditions prove the effectiveness of the proposed circuit.

• 전력전자학회논문지
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• 제12권1호
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• pp.98-106
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• 2007

본 논문에서는 개선된 온라인 턴 오프각 제어방식을 이용하여 스위치드 릴럭턴스 전동기의 성능최적화를 위한 온라인 전류제어방식을 제안한다. 성능최적화를 위한 제어방식은 에너지효율의 최대화와 토크리플 저감이라는 두가지 측면에서 접근하며, 두 가지 조건을 모두 만족할 수 있는 최적의 턴 오프 위치각은 제안된 알고리즘의 연산방식을 통해 획득된 턴 오프각 제어기를 통해 구현됨으로서 SRM의 성능최적화를 이룬다. 제안된 제어기는 토크와 전류 특성, 자속변동의 정보와 같은 복잡한 데이터베이스나 SRM이 가지는 고유의 자화곡선을 요구하지 않는다는 장점을 가지며 제안된 연산 제어기를 시뮬레이션과 실험을 통해 실제 적용가능성과 그 타당성을 입증한다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.101-105
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• 2005

Hemming process, composed of flanging, pre-hemming and main hemming, is the last one of a series of forming processes conducted on the automotive panels, having a great influence on the outward appearance of them. The hem quality can be quantitatively defined by the hemming defects including turn-down, warp and roll-in. However, it is difficult to evaluate and predict the hem quality through the experimental measurement or the numerical calculation since the size of defects is very small. This study is focused on how to simulate in the finite element analysis (FEA) the same conditions as in the experiment. The FEA result on turn-down, that was obtained from a finite element model including the spring element linked to the flanging pad, had a good correlation with the experimental data. It was found that the radius of curvature of the flange deeply affects the final hem quality and therefore high rigidity of forming tools and tight assembling tolerance are highly recommended. An over-stroke of the main hemming punch is also proposed to reduce the turn-down.

• 대한기계학회논문집B
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• 제25권3호
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• pp.405-413
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside a rotating two-pass rectangular duct. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The objective of this study is to determine the effects of turning geometry with rotation for 0.0$\leq$Ro$\leq$0.24. The results reveal that the sharp-turn corner has the larger pressure drop and lower heat transfer in the post-turn region than those of the round-turn corner. The strong secondary flow enhances heat transfer for the round-turn corner. Coriolis force induced by the rotation pushes the high momentum core flow toward the trailing wall in the first passage with radially outward flow and toward the leading wall in the second passage with radially inward flow. Consequently, the high heat transfer rates are generated on the trailing surface and the leading surface in the first and second passage, respectively. However, the strong secondary flow due to the turning dominates the flow pattern in the second passage, thus the heat transfer differences between the leading and trailing surfaces are small with the rotation.

• Current Optics and Photonics
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• 제3권3호
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• pp.210-214
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• 2019

The allowable path-deviation time of aircraft in a free-space optical communication system has been estimated from various trajectories, using different values of aircraft speeds and turn rates. We assumed the existence of a link between the aircraft and a ground base station. First, the transmitter beam's divergence angle was calculated through two different approaches, one based on a simple optical-link equation, and the other based on an attenuation coefficient. From the calculations, the discrepancy between the two approaches was negligible when the link distance was approximately 110 km, and was under 5% when the link distance ranged from 80 to 140 km. Subsequently, the allowable path-deviation time of the aircraft within the tracking-error tolerance of the system was estimated, using different aircraft speeds, turn rates, and link distances. The results indicated that the allowable path-deviation time was primarily determined by the aircraft's speed and turn rate. For example, the allowable path-deviation time was estimated to be ~3.5 s for an aircraft speed of 166.68 km/h, a turn rate of $90^{\circ}/min$, and a link distance of 100 km. Furthermore, for a constant aircraft speed and turn rate, the path-deviation time was observed to be almost unchanged when the link distance ranged from 80 to 140 km.