• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1647-1649
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• 1998

This paper describes the power frequency voltage and its countermeasure when a 765 kV transmission line is directly connected to a 345 kV line and operated at 345 kV voltage. The summary of this result is as follows : The western route of 765 kV transmission line doesn't need any countermeasure to reduce the power frequency voltage at the receiving end. The eastern route of 765 kV transmission needs 100 Mvar(3 phase) capacity of shunt reactor at the receiving end to reduce the power frequency voltage. The use of shunt reactors in the 765 kV transmission lines has unexpected problems, one of which is induction of high voltages on a de-energized circuit of two parallel lines. This paper examined the problem of resonance on two parallel transmission circuits in one routes.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.2
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• pp.82-90
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• 2015

This paper proposes an efficient bi-directional DC/DC converter topology using multi-phase interleaved method for power storage system. The proposed converter topology is used for a power storage system using a vanadium redox flow battery(VRFB) and is configured to enable bidirectional power flow for charging and discharging of VRFB. Proposed DC/DC converter of the 4 leg method is reduced to 1/4 times the rating of the reactor and the power semiconductor device so can be reduce the system size. Also, proposed topology is obtained the effect of four times the switching frequency as compared to the conventional converter in each leg with a 90 degree phase shift 4 leg method. This can suppress the reduction of the life of the secondary battery because it is possible to reduce the current ripple in accordance with the charging and discharging of VRFB and may increase the efficiency of the entire system. In this paper, it proposed bidirectional high-efficiency DC/DC converter topology Using multi-phase interleaved method and proved the validity through simulations and experiments.

• Korean Journal of Psychosomatic Medicine
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• v.25 no.1
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• pp.63-72
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• 2017

Objectives : Attention-deficit hyperactivity disorder(ADHD) is characterized by significant impairments in executive functions, with a prevalence of approximately 3-5% of all children worldwide. The goal of this study was to examine the relationship between executive functions and electrophysiological activities in children and adolescents with ADHD. Methods : In 31 patients with ADHD, resting-state EEG was recorded, and Comprehensive Attention Test(CAT), Stroop Color-Word Inference Test(Stroop CWIT), Trail Making Test(TMT), and Wisconsin Card Sorting Test(CST) were administered. Korean version of the ADHD Rating Scale(K-ARS) was assessed. Results : Alpha and beta power positively correlated with the Attention Quotient(AQ), while delta power negatively correlated with AQ from CAT. In the Stroop CWIT, decreased delta power and increased beta power were related to higher performance. Power of the alpha band increased with higher TMT performance. Moreover, delta power negatively correlated with good performance on the CST, while alpha and high gamma band showed a positive correlation. Correlation with the parent-rating of ADHD symptoms showed a negative correlation between alpha power and higher scores on the K-ARS. Conclusions : These findings indicate that relative power in higher frequency bands of EEG is related to the higher executive function in children and adolescents with ADHD, while the association with the relative power in lower frequency bands of EEG seem to be vice versa. Furthermore, the findings suggest that QEEG may be a useful adjunctive tool in assessing patients with ADHD.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.3
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• pp.124-128
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• 1999

The object of the present study is to obtain a 20[kHz], 10[kW] rating, high efficiency induction heating system by high frequency serises-resonant inverter. Proposed is a topology that minimize a reactive power, by which direct iOIrt voltage is variable corresponding to the variation of the load, heated-object, and by which the switching of inverter is forced to follow a resonant frequency. And assured that the power foctor of the inverter in a induction heating system is proper about O.96 through the simulation and results.esults.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.59-60
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• 2014

In this paper, development of laser diode driver with 2.5kW rating is presented. The driver is configured with interleaved PFC converter, high frequency full bridge DC-DC converter, two laser diode drivers and ${\mu}$-processor based controller. The system has two laser diode drivers for providing high current and low current. High current driver delivers normal output power of diode; low current driver is for providing critical current of diode for long lifetime. Computer simulation and experiment was performed for verification, as the results, developed driver performs well.

• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.43-45
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• 1998

ADD has developed a special BLDCM(brushless d.c. motor) that has small size and high power density. The model of BLDCM is like that of advanced nation. Design, production and test carried out with ADD and HICO. Now the performance of BLDCM is achieved 65% of design data. Also we are concerned with adhesion of magnet in rotor for high speed.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.5
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• pp.404-411
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• 2020

Inductive power transfer (IPT) systems for electric vehicles generally require zero phase angle (ZPA) frequency tracking control to achieve high efficiency. Current sensors are used for ZPA frequency tracking control. However, the use of current sensors causes several problems, such as switching noise, degrading control performance, and control complexity. To solve these problems, this study proposes ZPA frequency tracking control without current sensors. Such control enables ZPA frequency tracking without real-time control and achieves stable zero voltage switching operation closed to ZPA frequency within all coupling coefficient and load ranges. The validity of the proposed control algorithm is verified on LCCL-S topology with a 3.3 kW rating IPT experimental test bed. Simulation verification is also performed.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.359-360
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• 2015

10kV IGCT has been recently developed and has the potential to push wind turbine systems to higher power and voltage rating. Converters employing IGCTs need snubber and OVP circuit to limit the rate of rise of current and peak over voltage across IGCT during turn on and off state respectively. The conventional RCD snubber which is used in such power converter dissipates a significant amount of power. In order to reduce the amount of energy lost by conventional RCD snubber, this paper proposes an isolated inductor snubber circuit that not only meets all of the IGCTs characteristics during on and off-state but also significantly saves the power loss. Loss analysis of conventional di/dt snubber and OVP circuit is performed for the 3-level NPC type back-to-back VSC supplied from grid voltage of 6.9kV. In comparison with the conventional snubber, isolated inductor snubber has a fewer number of components and improved efficiency leading to a reliable and efficient wind turbine systems.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.5
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• pp.21-27
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• 2014

Currently, wind power has become a major research field in the area of sustainable development. As one important component of a wind turbine transmission system, most instances of downtime due to a gearbox failure are caused by bearing failures. Gearboxes for wind turbines must have the highest levels of reliability over a period of approximately 20 years, withstanding high dynamic loads. At the same time, a lightweight design and cost minimization efforts are required. These demands can only be met with a well-thought-out design, high-quality materials, a high production quality and proper maintenance. In order to design a reliable and lightweight gearbox, it is necessary to analyze methods pertaining to the bearing rating lifetimes of the standard and of different companies, also including calculation methods for modification factors. This can determine the influence of the bearing lifetime.

• Journal of Power Electronics
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• v.14 no.1
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• pp.30-39
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• 2014

This paper studies a new three-level pulse-width modulation (PWM) resonant converter for high input voltage and high load current applications. In order to use high frequency power MOSFETs for high input voltage applications, a three-level DC converter with two clamped diodes and a flying capacitor is adopted in the proposed circuit. For high load current applications, the secondary sides of the proposed converter are connected in parallel to reduce the size of the magnetic core and copper windings and to decrease the current rating of the rectifier diodes. In order to share the load current and reduce the switch counts, three resonant converters with the same active switches are adopted in the proposed circuit. Two transformers with a series connection in the primary side and a parallel connection in the secondary side are adopted in each converter to balance the secondary side currents. To overcome the drawback of a wide range of switching frequencies in conventional series resonant converters, the duty cycle control is adopted in the proposed circuit to achieve zero current switching (ZCS) turn-off for the rectifier diodes and zero voltage switching (ZVS) turn-on for the active switches. Finally, experimental results are provided to verify the effectiveness of the proposed converter.