• Journal of Power Electronics
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• 제7권4호
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• pp.318-327
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• 2007

The design and performance analysis of a power factor corrected (PFC), single-phase, single switch flyback buck-boost ac-dc converter is carried out for low power battery charging applications. The proposed configuration of the flyback buck-boost ac-dc converter consists of only one switch and operates in discontinuous current mode (DCM), resulting in simplicity in design and manufacturing and reduction in input current total harmonic distortion (THD). The design procedure of the flyback buck-boost ac-dc converter is presented for the battery charging application. To verify and investigate the design and performance, a simulation study of the flyback buck-boost converter in DCM is performed using the PSIM6.0 platform. A laboratory prototype of the proposed single switch flyback buck-boost ac-dc converter is developed and test results are presented to validate the design and developed model of the system.

• Journal of Industrial Technology
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• 제32권A호
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• pp.103-107
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• 2012

Due to improvement of the semiconductor technology, the LED replaces the conventional lighting source and LED drivers have been studied and developed. The LED is driven by the constant current control method according to its characteristics. For the constant current control method, the linear regulator and the switching regulator is used. The switching regulator is usually used to LED drivers because it has specific characteristics as the wide input dynamic range and the high efficiency. In this paper, we have described the principle and the implement of the switching regulator, using the drive IC and the low cost DSP chip. Also, both methods have been implemented and its electrical characteristics had almost same experimental results in the steady state and the transient state.

• Korean Journal of Materials Research
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• 제29권2호
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• pp.97-105
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• 2019

In the current steel structures of high-rise buildings, high heat input welding techniques are used to improve productivity in the construction industry. Under the high heat input welding, however, the microstructures of the weld metal (WM) and heat-affected zone (HAZ) coarsen, resulting in the deterioration of impact toughness. This study focuses mainly on the effects of fine TiN precipitates dispersed in steel plates and B addition in welding materials on grain refinement of the HAZ microstructure under submerged arc welding (SAW) with a high heat input of 200 kJ/cm. The study reveals that, different from that in conventional steel, the ${\gamma}$ grain coarsening is notably retarded in the coarse grain HAZ (CGHAZ) of a newly developed steel with TiN precipitates below 70 nm in size even under the high heat input welding, and the refinement of HAZ microstructure is confirmed to have improved impact toughness. Furthermore, energy dispersive spectroscopy (EDS) and secondary-ion mass spectrometry (SIMS) analyses demonstrate that B is was identified at the interface of TiN in CGHAZ. It is likely that B atoms in the WM are diffused to CGHAZ and are segregated at the outer part of undissolved TiN, which contributes partly to a further grain refinement, and consequently, improved mechanical properties are achieved.

• Korean Journal of Construction Engineering and Management
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• 제13권4호
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• pp.16-24
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• 2012

The objective of this paper is to suggest the improvement of estimating system for construction management (CM) service fee through the analysis of the previous literatures and criteria and case study. In order to do this, this paper considered the relevance of existing criteria to estimate the CM service fee, the condition of input ratio of engineering resources in the real cases, and current utilization strategy of nonresident technical engineers. Based on the analysis, the following problems were identified; a) the different estimating system for CM fee and construction supervision fee, b) impractical estimating system for the CM fee, and c) inappropriate allocation of human resources for CM. Consequently, this paper suggested the following 4 items for the improvement of the existing system; (1) modification of the current structure of CM fee calculation, (2) rationalization of current level of the CM fee which is required to be raised approximately 5.4 percent compared to design or supervision fee, (3) securement of elasticity of the input ratio of engineering resources from the inception phase, and (4) development of the utilization strategy of nonresident engineers based on the technical requirement of the jobsite. Thus, it is anticipated that this research would affect the compensation package of CM in order to make the estimation process of CM service fee more efficient and to revitalize CM as business.

• The Transactions of the Korean Institute of Electrical Engineers C
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• 제49권4호
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• pp.203-209
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• 2000

This paper proposes the improvement of the etch rate of GaN using a magnetized inductively coupled $CH_4/H_2/Ar$plasma. The gradient magnetic field with the axial direction is investigated using Gauss-meter and the ion current density is measured using double Langmuir probe. The applied magnetic field changes the ion current density profile in the radial direction, resulting in producing the higher density in the outer region than in the center. GaN dry etching process is carried out based on the measurements of the ion current density. The each rate of 2000 /min is achieved with $CH_4/H_2/Ar$ chemistries at 800 W input power, 250W rf bias power, 10 mTorr pressure and 100 gauss magnetic field.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제22권1호
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• pp.87-94
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• 2008

A method for improving current THD of Valley-fill rectifier is proposed in this paper. The proposed topology combines a boosting inductor with Valley-fill rectifier which carry out AC/DC conversion and PFC simultaneously The boosting effect by PWM switching makes low THD current and improve of Valley-fill rectifier. The operation modes and THD of input current are analyzed as applied the boosting inductor, and the optimum value of boosting inductor is determined A 100[W] single-stage converter has been designed and tested. Experimental results are resented to verify the validity of the proposed method.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.2224-2236
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• 2014

The performance of an isolated high voltage full bridge converter is improved using a voltage doubler. In a conventional high voltage full bridge converter, the diode of the transformer secondary voltage undergoes a voltage spike due to the leakage inductance of the transformer and the resonance occurring with the parasitic capacitance of the diode. In addition, in the phase shift control, conduction loss largely increases from the freewheeling mode because of the circulating current. The efficiency of the converter is thus reduced. However, in the proposed converter, the high voltage dual converter consists of a voltage doubler because the circulating current of the converter is reduced to increase efficiency. On the other hand, in the proposed converter, an input current is distributed when using parallel input / serial output and the output voltage can be doubled. However, the voltages in the 2 serial DC links might be unbalanced due to line impedance, passive and active components impedance, and sensor error. Considering these problems, DC injection is performed due to the complementary operations of half bridge inverters as well as the disadvantage of the unbalance in the DC link. Therefore, the serial output of the converter needs to control the balance of the algorithm. In this paper, the performance of the conventional converter is improved and a balance control algorithm is proposed for the proposed converter. Also, the system of the 1.5[kW] PCS is verified through an experiment examining the operation and stability.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제20권1호
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• pp.34-40
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• 2006

This paper proposed power system for new DC 49[V] telecommunication using forward three-phase PWM rectifier power factor and efficiency for improvement of ripple voltage. Proposed power system for DC 48[V] telecommunication that consists of power conversion devices including switch, inductor and condenser were made between each line, in power inverter device of each switch control turn-on in period of continuity time control to get power factor '1' of sine wave current and on-off of switch lessens peak current that was happened and got conversion efficiency 92.1[%] composing in PWM rectifier of forward form instead of general PWM rectifier. Also, harmonic input regulation value(IEC61000-3-2 Class-As) satisfy input current and reduce ripple factor of output voltage in state that distortion of three-phase supply is overlapped each other.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• 제8권5호
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• pp.35-41
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• 2008

This paper presents the design method of current-mode signal processing for high speed and low power digital audio signal processing. The digital audio processor requires a digital signal processing such as fast Fourier transform (FFT), which has a problem of large power consumption according to the settled point number and high speed operation. Therefore, a current-mode signal processing with a switched Current (SI) circuit was employed to the digital audio signal processing because a limited battery life should be considered for a low power operation. However, current memory that construct a SI circuit has a problem called clock-feedthrough. In this paper, we examine the connection of dummy MOS that is the common solution of clock-feedthrough and are willing to calculate the relation of width between dummy MOS for a proposal of the design methodology for improvement of current memory. As a result of simulation, in case of that the width of memory MOS is 20um, ratio of input current and bias current is 0.3, the relation of width between switch MOS and dummy MOS is $W_{M4}=1.95W_{M3}+1.2$ for the width of switch MOS is 2~5um, it is $W_{M4}=0.92W_{M3}+6.3$ for the width of switch MOS is 5~10um. Then the defined relation of MOS transistors can be a useful design guidance for a high speed low power digital audio processor.

• The Transactions of The Korean Institute of Electrical Engineers
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• 제60권3호
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• pp.524-530
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• 2011

This paper analyzes fault tolerance under a stator turn fault, according to the winding configuration. Improvement of torque characteristics and fault tolerance can be achieved by winding configuration without additional methods. And, torque characteristics and fault tolerance according to the winding configuration can be usually analyzed by analytical method. But, when the stator turn fault generates, compare to the steady-state, analysis of torque characteristics and fault tolerance using the analytical method is not accurate because it does not reflect influence in mutual inductance and magnetic non-linearity. Therefore, analysis of torque characteristics and fault tolerance has to be performed by using the numerical method under fault condition. This paper develops fault characteristics according to the winding configuration using the FEM-base model considered magnetic non-linearity. And, this paper suggests fault tolerance improvement according to the winding configuration, by the comparison of 8/12 and 10/12 models, under fault condition.