• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.71-72
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• 2015

본 논문에서는 전자기유도현상을 이용한 에너지 하베스터의 AC 출력 전압을 DC 전압으로 바꾸는 고효율 정류회로를 제안한다. 하베스터에서 다이오드의 문턱전압보다 낮은 전압이 생산될 수도 있을 뿐더러, 더 높은 전압이 생산된다 해도 결국 다이오드 정류를 거치면 엄청난 손실이 생기기 때문에 기존의 다이오드를 이용한 정류회로는 작은 AC 전압을 생산해내는 전자기유도현상을 이용한 에너지 하베스터와는 맞지 않다. 따라서 제안하는 정류회로는 별도의 전원을 필요로 하지 않는 스위치 회로를 갖추어 MOSFET과 LC공진을 이용하여 부스팅 후 정류를 그 목적으로 한 고효율 정류회로이다. 본 논문에서는 MOSFET과 LC공진회로의 특성을 이용한 고효율 정류회로를 설계, 동작원리를 설명하고, PSIM 시뮬레이션을 통하여 그 유용성을 검증한다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.5
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• pp.64-72
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• 2008

In the three phase four wire system, voltage unbalance caused by the unbalanced load operation, gives rise to current unbalance and de-rates by the increase of machine's loss and eventually enlarges power capacity and besides has a bad effect on power quality. Power capacitor has been used for the power factor correction of inductive load and the voltage stability of power system. And it uses instead of power side for magnetic excitation of induction motor. If voltage unbalance keeps up, it affects on voltage stress at the power capacitor and finally can be caused breakdown. In this paper, we analysed that voltage and current of power capacitor increases by the voltage unbalance factor and its stress is growing more and more.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.4
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• pp.239-245
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• 2013

The data retention characteristics depending on neighbor cell's threshold voltage (Vt) in a multilevel NAND flash memory is studied. It is found that a Vt shift (${\Delta}Vt$) of the noted cell during a thermal retention test is increased as the number of erase-state (lowest Vt state) cells surrounding the noted cell increases. It is because a charge loss from a floating gate is originated from not only intrinsic mechanism but also lateral electric field between the neighboring cells. From the electric field simulation, we can find that the electric field is increased and it results in the increased charge loss as the device is scaled down.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.1
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• pp.69-75
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• 2009

This paper studies the aerodynamic performance that the vent mixer-new conceptual supersonic mixer-showed with its geometric characteristics. The hole is 2 mm with 2 mm's distance from the wall in case 1 and with no distance in case 2. In case 3 die hole is 1 mm. Case 1 and case 2 showed the same total pressure recovery ratio, of which the case 3 was lower than that. While cases 1-3 had the same reattachment length, the shear layer was thicker in cases 1 and 2 than in case 3. Within the recirculation zone, cases 1 and 2 had lower pressure loss and higher velocity gradient difference than case 3-they enhance mixing between air and fuel. Separation bubble which is developed by the inflow into the recirculation zone has a significant effect on the total pressure recovery ratio in the combustor. Also separation bubble influences pressure distributions and recirculation flows in the recirculation zone. Therefore, inflow rate of air into the recirculation zone mainly affects the performance of vent mixer.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.6
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• pp.26-33
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• 2008

This paper presents a new full-bridge soft switching PWM DC-DC converter circuit topology that adding one switcher, one lossless snubber quasi-resonance capacity to power source for general welding machine This full-bridge soft switching DC-DC convoter· topology can applicable 600[V] switching device (IGBT)incase of AC 400[V] common power source because the voltage of active switcher is 1/2 of DC bus line voltage. And low voltage hight current out)ut that first coil current is smaller than second coil current in high frequency transformer can be obtained with decreasing path loss in conventional DC bus line switcher. As it operate ZCS/ZVS in full range, high frequency, high efficiency and high output are implemented at low voltage and high DC current switching power supplies. All of this items are got from simulation and the result of experiment. If make up for the weak points of this proposed circuit, it will be used more easily for next generation TIG, MIG and MAG type of arc-welding machine.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.4
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• pp.336-343
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• 2009

Secondary flow losses can be as high as 30~50% of the total aerodynamic losses generated in the cascade of a turbine. Therefore, these are important part for improving a turbine efficiency. As well, many studies have been performed to decrease the secondary flow losses. The present study deals with the leading edge fences on a wing-body to decrease a horseshoe vortex, one of the factors to generate the secondary flow losses, and investigates the characteristics of the generated horseshoe vortex as the shape factors, such as the installed height, and length of the fence. The study was investigated using $FLUENT^{TM}$. Total pressure loss coefficient was improved about 4.0 % at the best case than the baseline.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.2
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• pp.8-18
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• 1997

In this paper, a New Low Loss Quasi-Parallel Resonant DC-Link(NLQPRDCL) Inverter which shows highly improved PWM capability, low loss characteristic and low voltage stress is presented. A method to minimize freewheeling interval, which is able to largely decrease DC-link operation losses and to steadily guarantee soft switching in the wide operation region is also proposed. In addition, lossless control of zero voltage duration of DC-link makes the proposed inverter maintain the advanced PWM capability even under a very low modulation index. Experiment and simulation were performed to verify validity of the proposed inverter topology.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.33-36
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• 2010

Lots of studies about turbine loss have been done especially about tip leakage loss. But these studies deals with small tip clearances which is less than 5 percent chord. Now, like turbopumps, small turbines have larger tip clearance and it is hardly found related papers in open literature. On this study, with varying tip clearance 1% to 20% chord, loss is measured under inlet velocity at 30m/s and Reynolds number based on chord at 210000. It is found that maximum loss coefficient is 0.113 at 10% clearance, and when tip clearance is larger than 10%, loss is not linearly increased anymore.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.26-34
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• 2009

Secondary flow losses can be as high as 30~50% of the total aerodynamic losses for a turbo-machinery blade or stator row. These are important part for improving a turbine efficiency. Therefore, many studies have been performed to decrease the secondary flow losses. The present study deals with the chamfered leading-edge at a generic wing-body junction to decrease the horseshoe vortex, one of factors to generate the secondary flow losses, and investigates the vortex generation and the characteristics of the horseshoe vortex with the chamfered height, and depth of the chamfer by using $FLUENT^{TM}$. It was found that the total pressure loss for the best case can be decreased about 1.55% compare to the baseline case.

• Journal of the Korean Society for Railway
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• v.15 no.4
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• pp.357-363
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• 2012

This paper presents a new operation method for the single phase PWM(Pulse Width Modulation) converter train. Recently, the trains adopting the PWM converter have become the majority in the electric locomotives since there are distinct advantages over the predecessors, which can be operated at near unity power factor. However, a slight modification of the control scheme makes this kind of vehicles run in the region of leading power factor. Although this feature seems to be of no significant use by itself, the leading phase operation can improve the voltage profile and the line loss of the feeding systems is decreased by compensating the reactive power loss along the line when it considered together with the feeding systems. This method is even more economical and efficient comparing with the installation of SVC that is mainly used for this purpose since the train can become a movable compensator. With the conditions and some essential formula for the leading phase operation, a new power factor control algorithm has been proposed to implement this scheme. The results of simulation through SIMULINK model show that the proposed method is suitable enough for practical use.