• 전력전자학회:학술대회논문집
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• 전력전자학회 2012년도 전력전자학술대회 논문집
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• pp.29-30
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• 2012

In this paper, a performance of bi-directional DC/DC converter using PFM control at whole load range is analyzed. A bi-directional DC/DC converter using PFM control in this paper can be soft switching operation with LC series resonant circuit. It's difficult to expect a high efficiency at whole load range in general resonant converter because of limitation of soft switching area. Therefore converter used in this paper has a variable frequency PFM control to overcome a limitation of soft switching area and it makes a high efficiency at whole load range by implementing a soft switching at light load area of restricted soft switching. The high efficiency at whole load range is verified by simulation and experimental result.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권4호
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• pp.272-281
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• 2000

This paper deals with the parallel operation of several numbers of PWM converters for a high speed railway train application. Several considerations are made to reduce the transformer interaction which can cause a current control problem in severe case. Also, in this paper, novel control strategy is proposed to achieve a harmonic free primary-side current control under a light load condition using one current sensor independent of the number of converters. In addition, the modified predictive current controller, which is suitable to a digital current controller with a relatively large sampling period, is used. Finally, to verify the system validity, digital control system with TMS320C44 micro-processor and small scale simulator are made and tested.

• 한국안전학회지
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• 제32권5호
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• pp.41-46
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• 2017

The coefficient of derailment and the rate of wheel load reduction were used as the index of train running safety that was directly affected the train derailment safety. In aspects of track, the train running safety depends on the complex interaction between wheel and rail, and the track-vehicle conditions (i.e., the curvature, cant, track system, vehicle speed and the operation conditions, etc). In this study, the relationship between the train running safety and the track curvature and vehicle speed for direct fixation concrete tracks currently employed in Korean light rapid transit was assessed by performing field tests using actual vehicles running along the service lines. The measured dynamic wheel load, lateral wheel load and lateral displacement of rail head were measured for same train running on four tested tracks under real conditions, which included curved and tangent tracks placed on the tunnel and bridge, thus increasing the train speed by approximately maximum design speed of each test site. Therefore, the measured dynamic track response was applied to the running safety analysis in order to evaluate the coefficient of derailment, the rate of wheel load reduction and the track gauge widening at each test site, and compare with the corresponding Korean train running safety standard. As the results, the lateral track response of direct fixation concrete track appeared to increase with the decreased track curvature; therefore, it was inferred that the track curvature directly affected the train running safety.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 전력전자학술대회 논문집
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• pp.375-376
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• 2014

본 논문은 전동기의 V/F 운전시 발생하는 경부하 진동을 억제하는 방법을 제안한다. 제안한 방법은 기존의 무부하 전류를 사용하는 방법을 변형하여 V/F 운전시 전원 및 기계적 진동에 의해 발생하는 경부하 진동을 억제하여 운전 특성을 향상시킨다. 제안한 방법을 적용한 V/F 운전 특성을 실험을 통하여 검증하고 기존의 V/F 운전 대비 개선된 성능을 비교 분석한다.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1656-1663
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• 2016

A capacitive wireless power transfer (C-WPT) system uses an electric field to transmit power through a physical isolation barrier which forms a pair of ac link capacitors between the metal plates. However, the physical dimension and low dielectric constant of the interface medium severely limit the effective link capacitance to a level comparable to the main switch output capacitance of the transmitting circuit, which thus narrows the soft-switching range in the light load condition. Moreover, by fundamental limit analysis, it can be proved that such a low link capacitance increases operating frequency and capacitor voltage stress in the full load condition. In order to handle these problems, this paper investigates optimal design of double matching transformer networks for C-WPT. Using mathematical analysis with fundamental harmonic approximation, a design guideline is presented to avoid unnecessarily high frequency operation, to suppress the voltage stress on the link capacitors, and to achieve wide ZVS range even with low link capacitance. Simulation and hardware implementation are performed on a 5-W prototype system equipped with a 256-pF link capacitance and a 200-pF switch output capacitance. Results show that the proposed scheme ensures zero-voltage-switching from full load to 10% load, and the switching frequency and the link capacitor voltage stress are kept below 250 kHz and 452 V, respectively, in the full load condition.

• 대한인간공학회지
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• 제29권4호
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• pp.639-646
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• 2010

The APAM's quantitative effectiveness and comparative study in preventing and treating pressure ulcer has not been sufficiently evaluated mainly because of uncertainty of pressure load input and lack of interpretation of dynamic perfusion recovery characteristics of soft tissue. The purpose of this paper was to quantify and analyze the alternating pressure characteristics of APAM as a preventive measure for pressure ulcers. To quantify the alternating load to human body, we introduced alternating pressure profile concept and developed parametric model of the profile. Regarding pressure level and cycle time, 3 global and 7 local periodic parameters were used to define the profile such as light, standard, typical and heavy duty profile shape. Pressure impulse ratio of light duty is the lowest but pressure fluctuation is significantly high. For the same duty shape, contact conditions are changed with alternating cycle time and more dramatically in shorter alternating cycle time conditions. We can conclude that if we use shorter alternating cycle time on APAM's operation we can get more positive effects regarding to inflated contact time condition. We proposed the quantitative methods on tissue viability study of external loading by simultaneous measurement of interface pressure and tissue perfusion with proper alternating pressure profile conditions.

• 한국공간구조학회논문집
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• 제10권4호
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• pp.85-92
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• 2010

콘크리트의 사용은 건축 및 토목분야에서 널리 사용되어 왔으며, 센서는 콘크리트에 기능적 특성을 위해 사용되어 왔다. 손상을 스스로 나타내는 콘크리트는 이미 개발되고 있는 중에 있다. 본 연구에서 온도보상센서는 금속의 선형팽창과 체적변형을 이용한 센서이다. LED는 광센서로 고휘도이며, 이들 센서의 가격은 저가격이다. 화재하중으로 인하여 콘크리트 보의 온도보상센서가 동작하는 동안 지상 보의 LED동작으로 콘크리트 부재의 온도상승을 예측한다. 본 연구에서는 부재의 손상감지를 위해 간단한 계측방법을 이용하여 화재자현을 스스로 나타내는 콘크리트 보를 개발하기 위한 기초적 연구이다.

• 전력전자학회논문지
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• 제24권4호
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• pp.259-267
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• 2019

An active clamp flyback (ACF) converter applies a clamp circuit and circulates the energy of leakage inductance to the input side, thereby achieving a zero-voltage switching (ZVS) operation and greatly reducing switching losses. The switching losses are further reduced by applying a gallium nitride field effect transistor (GaN-FET) with excellent switching characteristics, and ZVS operation can be accomplished under light load with boundary conduction mode (BCM) operation. Optimal design is performed on the basis of loss analysis by selecting magnetization inductance based on BCM operation and a clamp capacitor for loss reduction. Therefore, the size of the reactive element can be reduced through high-frequency operation, and a high-efficiency and high-power-density converter can be achieved. This study proposes an optimal design for a high-efficiency and high-power-density BCM ACF converter based on GaN-FETs and verifies it through experimental results of a 65 W-rated prototype.

• Journal of Power Electronics
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• 제10권2호
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• pp.115-124
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• 2010

In this paper, a simple yet efficient auto mode-hop ripple control structure for buck converters with light load operation enhancement is proposed. The converter, which operates under a wide range of input and output voltages, makes use of a state-dependent hysteretic comparator. Depending on the output current, the converter automatically changes the operating mode. This improves the efficiency and reduces the output voltage ripple for a wide range of output currents for given input and output voltages. The sensitivity of the output voltage to the circuit elements is less than 14%, which is seven times lower than that for conventional converters. To assess the efficiency of the proposed converter, it is designed and implemented with commercially available components. The converter provides an output voltage in the range of 0.9V to 31V for load currents of up to 3A when the input voltage is in the range of 5V to 32V. Analytical design expressions which model the operation of the converter are also presented. This circuit can be implemented easily in a single chip with an external inductor and capacitor for both fixed and variable output voltage applications.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권2호
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• pp.292-300
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• 2015

This paper proposes a high-efficiency, dual-mode PWM / linear buck converter with a wide-input range. The proposed converter was designed with a mode selector that can change the operation between PWM / linear mode by sensing a load current. The proposed converter operates in a linear mode during a light load and in PWM mode during a heavy load condition in order to ensure high efficiency. In addition, the mode selector uses a bit counter and a transmission gate designed to protect from a malfunction due to noise or a time-delay. Also, in conditions between $-40^{\circ}C$ and $140^{\circ}C$, the converter has variations in temperature of $0.5mV/^{\circ}C$ in the PWM mode and of $0.24mV/^{\circ}C$ in the linear mode. Also, to prevent malfunction and breakdown of the IC due to static electricity, the reliability of IC was improved by embedding a self-produced 8 kV-class(Chip level) ESD protection circuit of a P-substrate Triggered SCR type with high robustness characteristics.