• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 ICEIC The International Conference on Electronics Informations and Communications
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• pp.221-224
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• 2004

This paper proposed an ultra low-power CMOS exponential voltage-mode circuit using the Pseudo-exponential function for realizing the exponential characteristics. The proposed circuit provides high dB-linear output voltage range at low-voltage applications. In a $0.25\;\mu m$ CMOS process, the simulations show more than 35 dB output voltage range and 26 dB with the linearity error less than $\pm0.5\;dB.$ The average current consumption is less than 80 uA. The proposed circuit can be used for the design of an extremely low-power variable gain amplifier (VGA) and automatic gain control (AGC).

• 전력전자학회:학술대회논문집
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• 전력전자학회 2010년도 추계학술대회
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• pp.169-170
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• 2010

본 논문에서는 전기자동차(Electric Vehicle, EV)의 주요 에너지 공급원인 배터리를 안정적으로 충 방전하기 위한 모드 전환 기법을 제안한다. 제안된 모드 전환기법의 타당성을 검증하기 위해 일반적으로 차량 시스템에 사용되는 다상 방식의 양방향 컨버터를 이용하여 시뮬레이션을 수행하였다. 또한, 컨버터의 전류제어는 각 상의 인덕터 전류에 대해 평균전류모드제어(Average Current Mode Control) 방법을 적용하여 제어하였다.

• 한국수학교육학회지시리즈A:수학교육
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• 제45권3호
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• pp.319-343
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• 2006

The purpose of this study is to investigate how fifth and sixth graders recognize average and to find out suggestions for teaching/learning methods of average by examining which difference there is depending on the way of the word problem presentation. For the this purpose, was conducted experiment study with the way of the world problem presentation set up as experimental treatment. The conclusions drawn from the results obtained in the this study were as follows : First, since students who did not learn the regular course of average had various informal concepts already, it is needed to consider handling more various concepts of average in order to enable students to expand flexible thoughts. Second, compared with fifth and sixth graders showed a wide difference in informal concepts of average depending on the way of the word problem presentation. In expect data with given average, concepts of mean as algorithm, balance point, and mode indicated similar percentage, while in estimate average with given data, the percentage of students who showed the concept of mean was very high at 67.6%. That may be because problems related to mean in the current textbooks are items of 'estimate average with given data', so in types of 'estimate average with given data', students solve questions with mean as algorithm without considering situations of problems. This result suggests that it is necessary to diversify the way of the word problem presentation even in textbooks. Third, as a result of analyzing informal concepts of average, there was significant difference in grades. In addition, the results suggested that there would be difference in the concepts of average depending on gender or attributes of discrete quantity and continuous quantity.

• 전력전자학회논문지
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• 제20권2호
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• pp.182-192
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• 2015

This study develops a digital control scheme with power factor correction for a front-end converter in an electric vehicle battery charger. The front-end converter acts as the boost-type switching-mode rectifier. The converter assumes the two roles of the battery charger, which include power factor control and robust charging performance. The proposed control scheme consists of a charging control algorithm and a grid current control algorithm. The scheme aims to obtain unity input power factor and robust performance. Based on the linear average model of the converter, a constant-current constant-voltage charging control algorithm that passes through only one proportional-integral controller and a current feed-forward path is proposed. In the current control algorithm, we utilized a second band pass filter, a single-phase phase-locked loop technique, and a duty-ratio feed-forward term to control the grid current to be in phase with the grid voltage and achieve pure sinusoidal waveform. Simulations and experiments were conducted to verify the effectiveness of the proposed control scheme, both simulations and experiments.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.160-163
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• 2004

A passive lossless turn-on/turn-off snubber network is proposed for the boost PWM converter. Previous AC/DC PFC Boost Converter perceives feed forward signal of output for average current-mode control. Previous Boost Convertor, the Quantity of input current will be decreased by the decrease of output current in light load, and also Power factor comes to be decreased. Also the efficiency of converter will be decreased by the decrease of power factor. The proposed converter presents the good PFC, low line current harmonic distortions and tight output voltage regulations using energy recovery circuit. All of the semiconductor devices in the converter are turned on under exact or near zero voltage switching(ZVS). No additional voltage and current stresses on the main switch and main diode occur. To show the superiority of this converter is verified through the experiment with a 640W, 100kHz prototype converter.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.61-65
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• 2005

Existing test methods for thick-section specimens ( 4mm) have not provided precise compressive properties to date for the analysis and design of thick structure. A survey of the failure behaviour of such thick specimens revealed that the failure initiated at the top corner of the specimen and propagated down and across the width of the specimen as premature failure, not typically reported for thin compression specimens. In the current study, the premature failure was successfully avoided during compressive testing and the failure mode was quite similar regardless of increasing specimen thickness and specimen volume. Failure mode was similar regardless of increasing specimen thickness and specimen volume, i.e. brooming failure mode combined with longitudinal splitting, interlaminar cracking, fibre breakage and kinkband formation (fibre microbuckling). Nevertheless, average failure strengths of the specimens decreased with increasing specimen thicnkiness from 2mm to 8mm with the T800/924C system (36% strength reduction) and specimen volumes from scaling factor I to scaling factor 4 with the IM7/8552 system (46% strength reduction). It was revealed from the literature$^{11}$ that the thickness effect and scaling effect arc caused by manufacturing defects such as void content and fibre waviness.

• Current Optics and Photonics
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• 제6권4호
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• pp.407-412
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• 2022

We report on a diode-laser-pumped mode-locked Yb:KGW laser system, which delivers ultrashort pulses down to 89 fs at a repetition rate of 63 MHz, with an average power of up to 5.6 W. A fiber-coupled diode laser at 981 nm, operated with a compact driver, is used to optically pump the gain crystal via an off-axis parabolic mirror. A semiconductor saturable-absorber mirror is used to initiate the pulsed operation. Laser characteristics such as the pulse duration, spectrum bandwidth, and output power are investigated by varying the intracavity dispersions via changing the number of bounces between negative-dispersive mirrors within the cavity. Short pulses with a duration of 89 fs, a center wavelength of 1,027 nm, and 3.6 W of output power are produced at a group-velocity dispersion (GVD) of -3,300 fs². As the negative GVD increases, the pulse duration lengthens but the output power at the single-pulse condition can be enhanced, reaching 5.6 W at a GVD of -6,600 fs². Because of pulse broadening at high negative GVDs, the highest peak intensity is achievable at a moderate GVD with our system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권3호
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• pp.958-979
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• 2023

Due to laws, regulations, privacy, etc., between 70-90 percent of providers do not share medical data, forming a "data island". It is essential to collaborate across multiple institutions without sharing patient data. Most existing methods adopt distributed learning and centralized federal architecture to solve this problem, but there are problems of resource heterogeneity and data heterogeneity in the practical application process. This paper proposes a collaborative deep learning modelling method based on the blockchain network. The training process uses encryption parameters to replace the original remote source data transmission to protect privacy. Hyperledger Fabric blockchain is adopted to realize that the parties are not restricted by the third-party authoritative verification end. To a certain extent, the distrust and single point of failure caused by the centralized system are avoided. The aggregation algorithm uses the FedProx algorithm to solve the problem of device heterogeneity and data heterogeneity. The experiments show that the maximum improvement of segmentation accuracy in the collaborative training mode proposed in this paper is 11.179% compared to local training. In the sequential training mode, the average accuracy improvement is greater than 7%. In the parallel training mode, the average accuracy improvement is greater than 8%. The experimental results show that the model proposed in this paper can solve the current problem of centralized modelling of multicenter data. In particular, it provides ideas to solve privacy protection and break "data silos", and protects all data.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 추계학술대회 논문집
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• pp.1-2
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• 2014

In this paper the partial switching PFC converter which is based on predictive control is proposed. In terms of satisfying the harmonic standard, the predictive control shows a similar performance to the conventional average current mode control PFC in the normal input condition. Moreover, the current harmonic characteristic is insensitive to the distorted input voltage. With predictive control method, novel on-line partial switching strategy is suggested in this paper. Depending on the operating condition, the partial switching PFC converter can boost its output voltage. Also when its efficiency needs to be improved, according to load condition, the partial switching can be achieved. The proposed strategy is proved by the results of FFT and the loss analysis using PSIM 9.0.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 C
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• pp.1560-1561
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• 2006

A high rate deposition sputtering process of magnesium oxide thin film in oxide mode has been developed using a 20 kW unipolar pulsed power supply. The power supply was operated at a maximum constant voltage of 500 V and a constant current of 40 A. The pulse repetition rate and the duty were changed in the ranges of $10{\sim}50\;kHz$ and $10{\sim}60%$, respectively. The deposition rate increased with rising incident power to the target. Maximum incident power to the magnesium target was obtained by the control of frequency, duty and current. The deposition rate of a moving state was 9 nm m/min at the average power of 1.5 kW.