• Journal of Power Electronics
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• v.18 no.1
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• pp.266-276
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• 2018

This paper presents a new step-up and step-down multi-pulse auto-transformer rectifier unit (ATRU) topology. This structure can achieve a wide range of output voltages, which solves the problem of auto-transformer output voltage being difficult to regulate. Adding middle taps to the primary winding and reasonably setting the number of auto-transformer windings, constituted two groups of three-phase output voltages with a $30^{\circ}$ phase difference. Multi-pulse output DC voltage is obtained after a three-phase output voltage across two rectifier bridges and inter-phase reactor. Thus, the output DC voltage is related to the number and configuration of the auto-transformer winding. In this paper, the relationship between the voltage ratio of the auto-transformer and the ratio of winding, input current and auto-transformer kilovoltampere rating are deduced and validated by simulations. On this basis, the output voltage range is optimized. An experiment on two different voltage ratio principle prototypes was carried out to verify the correctness of the analysis design.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.11B no.3
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• pp.98-103
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• 2001

This paper presents the numerical analysis of piezoelectric devices using three-dimensional finite element analysis. The characteristic of piezoelectric transducer, such as mechanical displacement and electrical are analyzed and the validity is confirmed by experiments Applying the finite element routine to a piezoelectric transformer, the resonance features electrical impedance. the ratio of step-up voltage and vibration mode of piezoelectric transformer are calculated numerically By using three-dimensional finite element method effects of width variation to resonance features, electrical input impedance and the voltage step-up ratio for a piezoelectric transformer, can be considered in design procedure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.223-224
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• 2006

This paper present a new disk-type piezoelectric transformer. The input side of the transformer has a crescent-shaped electrode and the output side has a focused poling direction. This transformer has multi-layered structure. The piezoelectric transformers operated m each transformer's resonance vibration mode. The electrodes and poling directions on commercialy available piezoelectric ceramic disks were designed so that the planar or shear mode coupling factor ($k_p,\;k_{15}$) becomes effective rather than the transverse mode coupling factor ($k_{31}$). The Resonance frequency is 65.22[kHz] and maximum voltage step-up ratio is 149. Multi-layered transformer has better efficiency and step-up ratio than the single-layered transformer.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1468-1479
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• 2015

Renewable energy resources such as wind and photovoltaic power generation systems demand a high step-up DC-DC converters to convert the low voltage to commercial grid voltage. However, the high step-up converter using a transformer has limitations of high voltage stresses of switches and diodes when the transformer winding ratio increases. Accordingly, conventional studies have been applied to series-connect multioutput converters such as forward-flyback and switched-capacitor flyback to reduce the transformer winding ratio. This paper proposes new single-ended converter topologies of an isolation type and a non-isolation type to improve power efficiency, cost-effectiveness, and output ripple. The first proposal is an isolation-type charge-pump switched-capacitor flyback converter that includes an extreme-ratio isolation switched-capacitor cell with a chargepump circuit. It reduces the transformer winding number and the output ripple, and further improves power efficiency without any cost increase. The next proposal is a non-isolation charge-pump switched-capacitor-flyback tapped-inductor boost converter, which adds a charge-pump-connected flyback circuit to the conventional switched-capacitor boost converter to improve the power efficiency and to reduce the efficiency degradation from the input variation. In this paper, the operation principle of the proposed scheme is presented with the experimental results of the 100 W DC-DC converter for verification.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1182-1184
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• 1992

In case of chopper control is used for the d.c motor In the electric vehicle(EV) in general step down chopper is used for the driving and the step-up chopper is used for the regeneration. Bilateral variable ratio chopper system(BVRCS) formed by parallel combination of upper two chopper methods step-down, step-up and step-up/down chopper operations by duty cycle, circuit element and driving condition. In this paper, BVRCS is proposed for the simulated and experimented control of d.c motor in the EV. By the result of simulation BVRCS represents same driving power compared to the step-down and excellent breaking power compared to the step-up chopper system because of the greater motor current.

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.167-178
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• 2000

An experimental study on step up filling method is carried out to reinforce the Yano method which is widely used to estimate volume ratio and self-weight consolidation settlement in reclamation area. This method considers actual reclamation construction in which dredged clay is continuously filled and rising of deposit height is presented as a result of volume decrease by height rising and self-weight consolidation. It measured the relationship between filling velocity and deposit rising velocity; calculated the total filling height which is needed to achieve the planned final deposit height, and its solid height and the time which is taken to finish the planned final deposit height; and on the basis of these calculated parameters, predicted the self-weight consolidation and volume change ratio in reclamation construction. Yano method is also used to predict the same conditions. 29.8% in self-weight consolidation, 31.1% in volume ratio, 40% in void ratio and water content is underestimated in Yano method compared to step up filling method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.8
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• pp.70-75
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• 2015

High Step-up DC-DC Converters have been demanded for renewable energy applications. Transformer or coupled inductor is generally used to boost output voltage of converters. This methods can relatively obtain high voltage than others, whereas have heavy weight and high cost. To complement these disadvantages, we studied transformerless high step-up DC-DC converter. In various transformerless topologies, Boost converters combined with Cockcroft-Walton have studied. In this paper, we proposed a symmetrical Cockcroft-Walton circuit for transformerless high step-up DC-DC converter. Finally, we simulated proposed converter to compare with existing converter. As a result, proposed converter has higher duty ratio or lower cost than existing transformerless converters which are discussed in this paper.

• Atmosphere
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• v.25 no.3
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• pp.473-482
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• 2015

In this study, street canyons with a higher downwind building (so called, step-up street canyons) are considered for understanding characteristics of flow and reactive pollutants' dispersion as a basic step to understand the characteristics in wider urban areas. This study used a CFD_NIMR_SNU coupled to a chemistry module just including simple $NO_X-O_3$ photochemical reactions. First, flow characteristics are analyzed in step-up street canyons with four aspect ratios (0.33, 0.47, 0.6, 0.73) defined as ratios of upwind building heights to downwind building height. The CFD_NIMR_SNU reproduced very well the main features (that is, vortices in the street canyons) which appeared in the wind-tunnel experiment. Wind speed within the street canyons became weak as the aspect ratio increased, because volume of flow incoming over the upwind building decreased. For each step-up street canyon, chemistry transport model was integrated up to 3600 s with the time step of 0.5 s. The distribution patterns of $NO_X$ and $O_3$ were largely dependent on the mean flow patterns, however, $NO_X$ and $O_3$ concentrations were partly affected by photochemical reactions. $O_3$ concentration near the upwind lower region of the street canyons was much lower than background concentration, because there was much reduction in $O_3$ concentration due to NO titration there. Total amount of $NO_X$ in the street canyons increased with the aspect ratio, resulting from the decrease of mean wind intensity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.13-20
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• 1997

In this paper, the voltage step-up ratio, efficiency and input impedance of the PMN-PZT cert- mic transformer(PT) were investigated for the variation of resonant frequency according to lead resistance. The output voltage and voltage step-up ratio are increased with the the increase of load resistance. The efficiency of PT showed the maxinum value of 91% at R$_{L}$ of 500k$\Omega$X>

• Korean Journal of Metals and Materials
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• v.50 no.2
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• pp.152-158
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• 2012

The effect of current waveform on Cu filling into TSV (through-silicon via) and the bottom-up ratio of Cu were investigated for three dimensional (3D) Si chip stacking. The TSV was prepared on an Si wafer by DRIE (deep reactive ion etching); and its diameter and depth were 30 and $60{\mu}m$, respectively. $SiO_2$, Ti and Au layers were coated as functional layers on the via wall. The current waveform was varied like a pulse, PPR (periodic pulse reverse) and 3-step PPR. As experimental results, the bottom-up ratio by the pulsed current decreased with increasing current density, and showed a value of 0.38 on average. The bottom-up ratio by the PPR current showed a value of 1.4 at a current density of $-5.85mA/cm^2$, and a value of 0.91 on average. The bottom-up ratio by the 3-step PPR current increased from 1.73 to 5.88 with time. The Cu filling by the 3-step PPR demonstrated a typical bottom-up filling, and gave a sound filling in a short time.