• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.5
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• pp.352-358
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• 2018

A split-capacitor (SC) dual-active-bridge (DAB) converter is proposed in this study. The DC-link capacitors of input and output are split in the proposed converter. The primary and secondary windings of transformer are connected to the midpoints of the DC-links. Hence, the SC DAB converter can inherently prevent transformer from saturation. Although the switch current stress of the proposed converter is twice that of the conventional DAB converter, the switch voltage stress is reduced by half. Therefore, the proposed converter can reduce switching loss and achieve high efficiency in a high switching frequency. Given the SC structure, the proposed converter can readily be connected to neutral-point-clamped- or half-bridge-type converters. The topology of the proposed converter is presented and the operating principle is analyzed in detail. A 3-kW hardware prototype was built and tested to verify the performance of the proposed converter.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.1
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• pp.130-135
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• 2007

In order to examine the corrosiveness of tap water, we studied methods calculating various indices including calcium carbonate saturation indices, using RTW model and LPLWIN model. Indices such as LI, RI and AI could be computed using the RTW model, whereas the LPLWIN model could find indices as LI, LR and CCPP. With water quality data obtained from tap water of Han River and Nak-Dong River watersheds, based on the indices found from the models, the water quality of the Nak-Dong River is better than that of Han River in the point of resisting corrosiveness. Further, the water quality of winter is highly corrosive than that of summer, as long as the temperature rises up, the corrosiveness is reduced.

• Journal of Electrical Engineering and Technology
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• v.11 no.4
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• pp.898-904
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• 2016

In this study, we have dealt with a design characteristic of outer-rotor type permanent magnet (PM) motor applied for Engine Cooling Fan (ECF). When we design a motor with structure like this type, it is required as a requisite to consider 3-Dimensional (3-D) effect by implementing a non-linear Finite Element Analysis (FEA) due to a yoke-ceiling, which is perpendicular to the axis of rotation. We have analyzed identical models under three different conditions. The analysis has been performed through a non-linear 2-Dimensional (2-D) and 3-D FEA. Finally, the results have been compared with Back Electro-Motive Force (BEMF) value of actual motor model. As a result, a yoke-ceiling function as an additional flux path and the operating point on B-H curve of rotor material is shifted to non-saturation region relatively. Accordingly, magnetic flux linkage can be increased and motor size can be decreased under same input condition to satisfy ECF specification, such as torque.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1467-1476
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• 2019

Grid unbalanced faults can cause core saturation of power transformer and produce lower-order harmonics. These issues increase the electrical stress of power electronic devices and can cause a tripping of an entire HVDC system. In this paper, based on the positive-sequence and negative-sequence impedance model of a VSC-HVDC system as seen from the point of common connection (PCC), the resonance problem is analyzed and the factors determining the resonant frequency are obtained. Furthermore, to suppress over-voltage and over-current during resonance, a novel method using a virtual harmonic resistor is proposed. The virtual harmonic resistor emulates the role of a resistor connected in series with the commutating inductor without influencing the active and reactive power control. Simulation results in PSCAD/EMTDC show that the proposed control strategy can suppress resonant over-voltage and over-current. In addition, it can be seen that the proposed strategy improves the safety of the VSC-HVDC system under unbalanced faults.

• International journal of advanced smart convergence
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• v.9 no.4
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• pp.62-73
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• 2020

In this paper, we present electronic acupuncture needles we have developed using intelligence technology based on Bluetooth in order to allow anyone to simply receive customized remote diagnosis and treatment by clicking on the menu of the smartphone regardless of time and place. In order to determine the health condition and disease of patients, we have developed a software and a hardware of electronic acupuncture needles, operating on Bluetooth which transmits biometric data to oriental medical doctors using the functions of automatically determining pulse diagnosis, tongue diagnosis, and oxygen saturation; the functions are most commonly used in herbal treatment. In addition, using fuzzy logic and reasoning based on smartphones, we present in this paper an algorithm and the results of completion of hardware implementation for electronic acupuncture needles, appropriate for the body conditions of patients; the algorithm and the hardware implementation are for a treatment time duration by electronic acupuncture needles, an automatic determinations of pulse diagnosis, tongue diagnosis, and oxygen saturation, a function implementation for automatic display of acupuncture point, and a strength adjustment of electronic acupuncture needles. As a result of our simulation, we have shown that the treatment of patients, performed using an Electronic Acupuncture Needles based on intelligence, is more efficient compared to the treatment that was performed before.

• Journal of Ginseng Research
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• v.36 no.4
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• pp.461-468
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• 2012

In this study, photosynthetic parameters such as the net photosynthesis rate, stomatal conductance, intercellular $CO_2$ concentration, and transpiration rate were examined in selected ginseng varieties and/or lines that are resistant (Yunpoong, HTIR 1, HTIR 2, and HTIR 3) and susceptible (Chunpoong) to high temperature injury (HTI). The net photosynthesis rate increased with the increase in the light intensity in all the HTI-resistant and -susceptible ginseng lines with a light saturation point of $200\;{\mu}mol\;m^{-2}s^{-1}$, except for Yunpoong that had a light saturation point of $400\;{\mu}mol\;m^{-2}s^{-1}$. At the light saturation point, the net photosynthesis rate in July was highest in HTIR 3, at $4.2\;{\mu}mol\;CO_2\;m^{-2}s^{-1}$, and was lowest in Yunpoong, HTIR 1, Chunpoong, and HTIR 2, in that order, at 1.9 to $3.7\;{\mu}mol\;CO_2\;m^{-2}s^{-1}$. The net photosynthesis rate in August was highest in Yunpoong at $5.9\;{\mu}mol\;CO_2\;m^{-2}s^{-1}$, and lowest in HTIR 1 and HTIR 3 ($4.5\;{\mu}mol\;CO_2\;m^{-2}s^{-1}$) and in other lines, in that order, at 2.8 to $2.9\;{\mu}mol\;CO_2\;m^{-2}s^{-1}$. The stomatal conductance in July was highest in HTIR 3 (0.055 mol $H_2O\;m^{-2}s^{-1}$) and Yunpoong, Chunpoong, HTIR 1, and HTIR 2 were 0.038, 0.037, 0.031, and 0.017 in that orders. In August, meanwhile, HTIR 1 showed the highest as 0.075, and followed by HTIR 3, Chungpoong, and HTIR 2 with 0.070, 0.047, and 0.023, respectively. The intercellular $CO_2$ concentration at the light saturation point in July and August was much lower in HTIR 2 at 139 and $185\;{\mu}mol\;mol^{-1}$ than in the other ginseng lines at 217 to 257 and 274 to $287\;{\mu}mol\;mol^{-1}$, respectively. The transpiration rate in July and August was higher in the HTI-resistant lines of Yunpoong, HTIR 1, and/or HTIR 3 at 0.83 to 1.03 and 1.67 to 2.10 mol $H_2O\;m^{-2}s^{-1}$ than in the other ginseng lines at 0.27 to 0.79 mol $H_2O\;m^{-2}s^{-1}$ and 0.51-1.65 mol $H_2O\;m^{-2}s^{-1}$, respectively. Conclusively, all the photosynthetic parameters that were examined in this study were generally higher in the HTI-resistant ginseng lines than in the HTI-susceptible lines, except for HTIR 2, and were much higher in August than in July, especially in the resistant ginseng lines. All these results can be used to provide basic information for the selection of HTI-resistant ginseng lines and the application of cultural practices that are efficient for ginseng growth, based on the photosynthetic characteristics of the lines.

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.201-216
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• 2013

Ground penetrating radar (GPR) surveys were conducted in a sand tank model in a laboratory and at an alluvial field site to detect the groundwater table and to investigate the influence of saturation on GPR response in the unsaturated zone. In the sand tank model, the groundwater table and saturation in the sand layer were altered by injecting water, which was then drained by a valve inserted into the bottom of the tank. GPR vertical reflection profile (VRP) data were obtained in the sand tank model for rising and lowering of the groundwater table to estimate the groundwater table and saturation. Results of the lab-scale model provide information on the sensitivity of GPR signals to changes in the water content and in the groundwater table. GPR wave velocities in the vadose zone are controlled mainly by variations in water content (increased travel time is interpreted as an increase in saturation). At the field site, VRP data were collected to a depth of 220 m to estimate the groundwater table at an alluvial site near the Nakdong river at Iryong-ri, Haman-gun, South Korea. Results of the field survey indicate that under saturated conditions, the first reflector of the GPR is indicative of the capillary fringe and not the actual groundwater table. To measure the groundwater table more accurately, we performed a GPR survey using the common mid-point (CMP) method in the vicinity of well-3, and sunk a well to check the groundwater table. The resultant CMP data revealed reflective events from the capillary fringe and groundwater table showing hyperbolic patterns. The normal moveout correction was applied to evaluate the velocity of the GPR, which improved the accuracy of saturation and groundwater table information at depth. The GPR results show that the saturation information, including the groundwater table, is useful in assessing the hydrogeologic properties of the vadose zone in the field.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.820-829
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• 2017

Vegetable oil dielectrics have been used in transformers as green alternatives to mineral insulating oils for about twenty years, because of their advantages of non-toxic, biodegradability, and renewability. However, the viscosity of vegetable oils is more than 3 times of mineral oils, which means a poor heat dissipation capacity. To get low-viscosity dielectrics, transesterification and purification were performed to prepare vegetable oil methyl esters in this study. Electrical and physical properties were determined to investigate their potential as dielectrics. The results showed that the methyl ester products had good dielectric strengths, high water saturation and enough fire resistance. The viscosities (at $40^{\circ}C$) were 0.2 times less than FR3 fluid, and 0.7 times less than mineral oil, which indicated superior cooling capacity as we expected. With the assistance of 0.5 wt% pour point depressants, canola oil methyl ester exhibited the lowest pour point ($-26^{\circ}C$) among the products which was lower than FR3 fluid ($-21^{\circ}C$) and 25# mineral oil ($-23^{\circ}C$). Thus, canola oil methyl ester was the best candidate as a low-viscosity vegetable oil-based dielectric. The low-viscosity fluid could extend the service life of transformers by its better cooling capacity compared with nature ester dielectrics.

• Journal of the Mineralogical Society of Korea
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• v.24 no.1
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• pp.37-42
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• 2011

Magnetic properties at low-temperatures can diagnose the presence of certain magnetic minerals in rocks. At the Verwey transition temperature ($T_v$, ~105~120 K), magnetite transforms from monoclinic to cubic structure as the temperature increases. At the isotropic point ($T_i$, ~135 K), magnetocrystalline anisotropic constant of magnetite passes through zero (from negative to positive) as the temperature decreases so that its optimal remanence acquisition axis changes from [111] to [001]. A sharp remanence drop was observed at $T_v$ during warming of LTSIRM (low-temperature saturation isothermal remanent magnetization). For cooling of RTSIRM (room-temperature saturation isothermal remanent magnetization), the remanence decreased on passing $T_i$ and $T_v$. On warming of RTSIRM, remanence recovery becomes more prominent as the average grain size of magnetite increases. In summary, the SIRM memory decreases with increasing grain size of magnetite. A similar, but rather gradual, remanence transition occurs for natural samples due to contribution of cations other than Fe. As a non-destructive tool, low-temperature magnetic behavior is sensitive to unravel the magnetic remanence carriers in terrestrial rocks or meteorites.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.2
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• pp.135-140
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• 2010

A new treatment is proposed to handle a deflection limit in the open-loop-onset-point (OLOP), which is commonly used in the prediction of pilot in-the-loop oscillation (PIO) due to a rate saturation. The new approach is motivated by the frequency response of a stand-alone actuator in that, unlike the suggestion by the original OLOP procedure, the rate limit onset is not delayed to a higher frequency by a deflection limit. Indeed, if a feedback control loop is closed, the rate limit onset can be shifted to a lower frequency since the controller tends to react with larger commands when deflection limited. The amplitude of the command at this onset frequency is combined with the deflection limit to estimate the associated gain reduction in the open-loop-onset-point in the final step of the OLOP process. The comparison of the new approach with the previous method reveals that an inaccurate optimism which can occur in the previous method is corrected by the proposed treatment.