• Journal of the Ergonomics Society of Korea
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• v.28 no.3
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• pp.95-102
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• 2009

Ten young females were participated in this study to investigate the effects of types of shoes (sneakers, high heels, kill heels), types of tasks (standing, walking floor, step up and down), and areas of foot (fore foot, middle foot, rear foot) on foot pressures as well as subjective discomfort ratings. Results showed that kill heels had the most discomfort shoes, followed by high heels and sneakers. Generally, as the heel was higher, the discomfort of foot increased. For the analyses of task types, generally discomfort ratings were highest for the step down and up, followed by walking floor and standing. Especially discomfort ratings of high heels and kill heels were more evident in case of step up and step down than standing and walking floor. Standing task was rated as the lowest levels of discomfort on users' foot. Peak and mean foot pressures were also evaluated in this study. The findings represented that there was no significant differences between types of shoes in both peak and mean foot pressures. The peak pressure (82.14kPa) and mean pressure (40.32kPa) for standing task were significantly lower than those of other tasks [walking floor (190.55kPa, 55.46kPa), step up (191.43kPa, 53.80kPa), and step down (200.66kPa, 52.62kPa)]. Generally discomfort ratings and peak/mean pressures associated with foot showed that fore foot had higher discomfort ratings as well as peak and mean pressures than middle and rear foots. In particularly, this trend was more obvious in case of high heels and kill heels. For the high heels and kill heels, the peak pressures of fore foot were 4.5~4.8 times and 2.3~2.5 times greater than that of middle foot and rear foot, respectively, whereas the peak pressures of fore foot were 2.9 times and 1.7 times greater than that of middle and rear foots, respectively, in case of sneakers.

• Progress in Superconductivity and Cryogenics
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• v.19 no.4
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• pp.40-44
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• 2017

This paper analyzed the fault current limiting characteristics of the previously proposed transformer superconducting fault current limiter (TSFCL) interruption system according to its transformer type. The TSFCL interruption system is an interruption technology that combines a TSFCL, which uses a transformer and a superconductor, and a mechanical DC circuit breaker. This technology first limits the fault current using the inductance of the transformer winding and the quench characteristics of the superconductor. The limited fault current is then interrupted by a mechanical DC circuit breaker. The magnitude of the limited fault current can be controlled by the quench resistance of the superconductor in the TSFCL and the turns ratio of the transformer. When the fault current is controlled using a superconductor, additional costs are incurred due to the cooling vessel and the length of the superconductor. When the fault current is controlled using step-up and step-down transformers, however, it is possible to control the fault current more economically than using the superconductor. The TSFCL interruption system was designed using PSCAD/EMTDC-based analysis software, and the fault current limiting characteristics according to the type of the transformer were analyzed. The turns ratios of the step-up and step-down transformers were set to 1:2 and 2:1. The results were compared with those of a transformer with a 1:1 turns ratio.

• Journal of Power Electronics
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• v.18 no.2
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• pp.343-355
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• 2018

A wide-voltage-conversion range bidirectional DC-DC converter is proposed in this paper. The topology is comprised of one typical LC energy storage component and a special common grounded asymmetric H-bridge with four active power switches/anti-parallel diodes. The narrow output PWM voltage is generated from the voltage difference between two normal (wider) output PWM voltages from the asymmetric H-bridge with duty cycles close to 0.5. The equivalent switching frequency of the output PWM voltage is double the actual switching frequency, and a wide step-down/step-up ratio range is achieved. A 300W prototype has been constructed to validate the feasibility and effectiveness of the proposed bidirectional converter between the variable low voltage side (24V~48V) and the constant high voltage side (200V). The slave active power switches allow ZVS turn-on and turn-off without requiring any extra hardware. The maximum conversion efficiency is 94.7% in the step-down mode and 93.5% in the step-up mode. Therefore, the proposed bidirectional topology with a common ground is suitable for energy storage systems such as renewable power generation systems and electric vehicles with a hybrid energy source.

• Proceedings of the KIEE Conference
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• 2006.10c
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• pp.169-171
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• 2006

This paper studies the step motors moved up-down and fore-back direction and deals with a position control and tracking the trajectory of the robot. For simulation and experiment, we demonstrate core part with usefulness and effectiveness.

• Journal of the Chungcheong Mathematical Society
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• v.25 no.3
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• pp.475-489
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• 2012

A plateau in a Motzkin path is a sequence of three steps: an up step, a horizontal step, then a down step. We find three different forms for the bivariate generating function for plateaus in Motzkin paths, then generalize to longer plateaus. We conclude by describing a further generalization: a continued fraction form from which one can easily derive new multivariate generating functions for various kinds of path statistics. Several examples of generating functions are given using this technique.

• Journal of Power System Engineering
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• v.19 no.2
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• pp.15-21
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• 2015

Bollard installed on the street is a facility that protects pedestrians by restraining cars from entering on the sidewalk. It is basically classified into manual, semiautomatic, automatic type and mostly manual type is widely used because the automatic type is imported and much expensive. However, in case of manual handling type in practice, it is very troublesome and difficult to remove it whenever cars are permitted, and in case of automatic type, since underbody of a bollard is very long, it is difficult to dig a deep hole in the ground because a pipe, a hose or a cable is under the surface. In order to reduce these difficulties, this paper proposed new design of the multistage bollard that moves up and down automatically by using hydraulic system. This is developed by 6 step creativity of TRIZ inventive problem solving and structural analysis. The developed bollard can be installed in shallow hole and allow entry of vehicles through up-and-down movement without its removal manually. Finally, we could see smoothly motion through the manufactured bollard.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1629-1638
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• 2016

Differential power processing (DPP) systems are among the most effective architectures for photovoltaic (PV) power systems because they are highly efficient as a result of their distributed local maximum power point tracking ability, which allows the fractional processing of the total generated power. However, DPP systems require a high-efficiency, high step-up/down bidirectional converter with broad operating ranges and galvanic isolation. This study proposes a single, magnetic, high-efficiency, high step-up/down bidirectional DC-DC converter. The proposed converter is composed of a bidirectional flyback and a bidirectional isolated switched-capacitor cell, which are competitively cheap. The output terminals of the flyback converter and switched-capacitor cell are connected in series to obtain the voltage step-up. In the reverse power flow, the converter reciprocally operates with high efficiency across a broad operating range because it uses hard switching instead of soft switching. The proposed topology achieves a genuine on-off interleaved energy transfer at the transformer core and windings, thus providing an excellent utilization ratio. The dynamic characteristics of the converter are analyzed for the controller design. Finally, a 240 W hardware prototype is constructed to demonstrate the operation of the bidirectional converter under a current feedback control loop. To improve the efficiency of a PV system, the maximum power point tracking method is applied to the proposed converter.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.225-227
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• 2006

Multilayer step down piezoelectric transformers were manufactured using PZN-PMN-PZT and PMN-PNN-PZT ceramics respectively. Sintering temperature of the ceramics was $940^{\circ}C$. And then. their electrical properties were investigated according to the variations of frequency and load resistance. The voltage step-up ratio of multilayer piezoelectric transformer showed the maximum values in the vicinity of 69 and 71kHz, respectively. At the load resistance of $100{\Omega}$, the piezoelectric transformers showed the temperature rises of about 21 and $18^{\circ}C$ at the output power of 15W and 18W, respectively. At the transformer with high effective electromechanical coupling factor($k_{eff}$), lower temperature increase was appeared.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.4
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• pp.332-336
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• 2007

In this study, multilayer piezoelectric transformer was manufactured using the PMN-PNN-PZT ceramic and then the electrical characteristics were investigated according to the variations of frequency and load resistance. The voltage step-up ratio of multilayer piezoelectric transformer showed the maximum value at the vicinity of 75 kHz and increased according to the increase of load resistance. When the output impedance coincided with the load resistance, the multilayer piezoelectric transformer showed the temperature rise of less than $20^{\circ}C$ at the output power of 20 W. As the results, the multilayer piezoelectric transformer manufactured at low co-firing temperature of $940^{\circ}C$ using PMN-PNN-PZT ceramics could be stably driven as the step-down transformers.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.4
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• pp.322-329
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• 2012

This paper proposes a non-isolated bidirectional soft-switching converter with high voltage for high step-up/down and high power applications. Compared to the conventional boost converter the proposed converter can achieve approximately doubled voltage gain using the same duty cycle. The voltage ratings of the switch and diode are reduced to half, which result in the use of devices with lower $R_{DS(ON)}$ and on drop leading to reduced conduction losses. Also, voltage ratings of the passive components are reduced, and therefore the total energy volume is reduced to half. Further, the switch is turned on with ZVS in the CCM operation which results in negligible surge caused leading to reduced switching losses. The validity of the proposed converter is proved through a 10kW prototype.