• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.3
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• pp.358-366
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• 2014

This paper proposes a quasi Z-source AC-AC converter with the low DC voltage distribution capability operating as a power electronic transformer. The proposed system has configuration that the input terminals of two quasi Z-source AC-AC converters are connected in parallel, also their output terminal are connected in series. Simple control method of duty ratio was proposed for the in phase buck-boost AC voltage mode and the DC output voltage control. DSP based experiment and PSIM simulation were performed. As a result, the PSIM simulation results were same with the measured results. By controlling the duty ratio under the condition of 100 [${\Omega}$] load, quasi Z-source AC-AC converter could buck and boost the AC output voltage in phase with the AC input voltage, and the same time, the constant DC voltage could be output without affecting the AC output characteristics. And, the DC output voltage 48[V] was constantly controlled in dynamic state in case while the load is suddenly changed ($50[\Omega]{\rightarrow}100[\Omega]$). From the above result, we could know that the quasi Z-source AC-AC converter can act as a power electronic transformer with a low DC voltage distribution capability.

• Journal of Korean Ophthalmic Optics Society
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• v.18 no.2
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• pp.117-123
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• 2013

Purpose: The aim of this study was to propose effective data for the clinical examinations of binocular vision by comparative analysis of measuring the near horizontal phoria according to accommodative stimulations. Methods: It carried out near horizontal phorias, targeting 104 college students (50 males and 54 females) aged between 19 and 24 ($20.27{\pm}1.31$). It made a comparative analysis of changes in near horizontal phoria according to accommodative stimulations by using the von Graefe, Maddox rod and the Howell phoria methods respectively. We have also investigated the AC/A ratio in all phoria groups. Results: As the additional lenses were changed to the negative (-) diopter, the near horizontal phoria changed to the esodeviation. At this time, the rate of change in the section signifies the AC/A ratio, and the values were not consistent based on the evaluating methods or on each section. The AC/A ratio of the esophoria group appeared the largest value in all groups. As a result of analyzing AC/A ratio at the exophoria group using the von Graefe method, the AC/A ratio was $1.568{\pm}1.937$ ${\Delta}/D$ on the additional lenses +2.00 D and $2.527{\pm}2.253$ ${\Delta}/D$ on the additional lenses -1.00 D and at the esophoria group using the Howell phoria method, the AC/A ratio was $5.521{\pm}1.337$ ${\Delta}/D$, $5.593{\pm}1.623$ ${\Delta}/D$ on the additional lenses +2.00 D, +1.00 D and $4.687{\pm}1.643$ ${\Delta}/D$ on the additional lenses -2.00 D. These were significant differences statistically. Conclusions: In the exophoria group, when the (-) lenses were added, the averages of the AC/A ratio were shown to be high but in the esophoria group, when the (+) lenses were added, the of AC/A ratio was high.

• Journal of Power Electronics
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• v.19 no.1
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• pp.24-33
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• 2019

A new modeling method for AC-AC switched capacitor converters (SCCs) is introduced in this study. The proposed analytical method aims to accurately describe the input-output characteristics of AC-AC SCCs and establish a mathematical model for static voltage conversion ratio and equivalent resistance, which are key performance metrics for SCCs. A quantitative analysis of converter regulation capability is addressed on the basis of the modeling method. In this analysis, the effects of the control parameters and individual components on SCCs are illustrated extensively. Component stresses, such as the peak value and transient variation of the voltage/current of the converter, are also presented. The effectiveness of the proposed method is verified by comparing it with the existing modeling method and applying it to an AC-AC SCC with a conversion ratio of three. Two 1 kW prototypes are built in a laboratory, and their experimental results exhibit good agreement with the theoretical analysis.

• Journal of Digital Convergence
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• v.14 no.10
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• pp.375-380
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• 2016

This study aimed to evaluate the possibility for assessment of binocular visual function about alteration for near point of convergence (NPC). Study subjects were total 30 (emmetropia 16, myopia 14), who had no eye disease except for the phoria and monocular corrected vision 1.0 and over. Near point of accommodation (NPA), NPC and phoria test were measured both at ordinary and stimulation of +1D. Ordinary NPC was 1.77cm shorter than NPC stimulated +1D and the NPC of emmetropia was shorter than that of myopia. The difference between NPC stimulated +1D and ordinary were increased in the emmetropia. As the NPC increased, the AC/A ratio was elevated and the feature of near exophoria appeared. The results suggested that the alteration of NPC might substitute AC/A ratio for reference variable of binocular vision. If converged and analyzed comparatively with another binocular visual evaluation test, the alteration of NPC could be developed for substitution of evaluation test.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.350-355
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• 1998

Preplaced aggregate concrete in the building fields has recently been used in the partial repair works for damaged reinforced concrete structures, and polymer-modified mortars have been employed as grouting mortars for the preplaced aggregate concrete. The objective of this study is to clear the properties of polymer-modified grouting mortars. Polymer-modified mortars using a polystyrene acrylic(St/Ac) emulsion as grouting mortars for preplaced aggregate concrete are prepared with various mix proportions, and tested for flexural and compressive strengths, adhesion in tension. The flexural strength of emulsion-modified grouting mortars does not give much variation with increasing fly ash replacement for cement and sand-binder ratio. With increasing polymer-binder ratio, the flexural strength and adhesion in tension of St/Ac emulsion-modified grouting mortars increases, become nearly constant or reaches a maximum at a polymer-binder ratio of 5%. From the test results, St/Ac emulsion-modified grouting mortar with a polymer-binder ratio of 5%, a fly ash replacement of 10% for cement and sand-binder ratio of 1.0 is recommended as a grouting mortar for preplaced aggregate concrete.

• Korean Journal of Ophthalmology
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• v.32 no.6
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• pp.483-487
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• 2018

Purpose: To compare the characteristics and surgical outcomes in patients with tenacious proximal fusion (TPF) and high accommodative convergence/accommodation ratio (AC/A) types of intermittent exotropia. Methods: This study retrospectively enrolled 40 patients with intermittent exotropia, 23 with TPF and 17 with high AC/A. Binocular function was evaluated by Worth's 4-dot test. Patients underwent lateral rectus recession, and surgical outcomes were compared. Surgical success was defined as less than ${\pm}10$ prism diopters (PD) at 12 months postoperatively. Results: The proportion of diplopia at near, evaluated by Worth's 4-dot test, was significantly higher in patients with high AC/A than in those with TPF (35.3% vs. 4.3%, p = 0.029). The mean preoperative angles of deviation in TPF and high AC/A types were $28.3{\pm}4.4$ and $28.8{\pm}4.5PD$ at distances, and $14.7{\pm}4.2$ and $15.1{\pm}4.1PD$ at near. Twelve months after surgery, the mean angles of deviation in TPF and high AC/A types were $2.9{\pm}9.8$ and $1.2{\pm}9.6PD$, respectively, at distance and $1.7{\pm}7.7$ and $-1.3{\pm}11.3PD$ at near. The surgical success rates were similar in the TPF and high AC/A types (74.0% vs. 64.7%). Five (21.7%) patients with TPF and 2 (11.8%) with high AC/A type experienced recurrence, with consecutive esotropia occurring in 1 (4.3%) patient with TPF and 4 (23.5%) patients with high AC/A. Conclusions: The proportion of diplopia at near was higher in patients with high AC/A type than in those with TPF intermittent exotropia. However, the surgical success rates were not significantly different between the types.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.9
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• pp.434-440
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• 2005

This paper describes an optimized Scheme of reactive-power compensation for the low short-circuit-ratio AC system interconnected with the HVDC system. An HVDC system interconnected with tile low SCR AC system is vulnerable to the ac voltage variation, which brings about the commutation failure of the converter. This problem can be solved using optimized compensation of reactive power. In this study, a benchmark system for HVDC system interconnected with low SCR AC system is derived using PSS/E simulation. Then an optimized srheme for reactive power compensation was derived using integer programming. The feasibility of proposed scheme was analyzed through silnulations with PSS/E and PSCAD/EMTDC. The proposed scheme can compensate the reactive power accurately and minimize the number of switching for harmonic filters and shunt reactors.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.45 no.6
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• pp.88-94
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• 2008

A DCT-based energy-ratio measure for autofocus in digital camera is proposed in this paper. This measure, namely AC2DC1 and AC5DC1, determines the sharpness of an image using a ratio between AC and DC energy in the DCT domain. This method is derived from energy analysis of DCT coefficients. Autofocus score calculation method is used to assess the performance of the proposed measure and to compare it with other measures. Experimental results under various conditions verify the robustness of the proposed focus measure for the Gaussian as well as impulsive noises.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.784-785
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• 2015

This paper proposes a new structure of coil to maximize the conductor occupting ratio(conductor cross sectional area than the cross sectional area inside the slot) of the magnetic core. Further, assuming a case in which the 3-D coil is applied to a real motor. Analyze the current density distribution of the coil conductor by electromagnetic analysis method. Finally the AC resistance was measured according to the frequency of the coils. This expereiment is to calculate a optimal operating frequency to obtain high efficiency operational frequency range of motor.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.3
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• pp.247-255
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• 2013

In this paper, a soft switching DC-DC converter for AC module type photovoltaic (PV) module integrated converter is proposed. A push-pull converter is suitable for a low voltage PV AC module system because the step-up ratio of a high frequency transformer is high and the number of primary side switches is relatively small. However, the conventional push-pull converters do not have high efficiency because of high switching losses by hard switching and transformer losses (copper and iron losses) by high turns-ratio of the transformer. In the proposed converter, primary side switches are turned on at zero voltage switching (ZCS) condition and turned off at zero current switching (ZVS) condition through parallel resonance between secondary leakage inductance of the transformer and a resonant capacitor. Therefore the proposed push-pull converter decreases the switching loss using soft switching of the primary switches. Also, the turns-ratio of the transformer can be reduced by half using a voltage-doubler of secondary side. The theoretical analysis of the proposed converter is verified by simulation and experimental results.