• Journal of the Korean Society of Industry Convergence
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• v.24 no.4_1
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• pp.387-395
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• 2021

Distributed resources such as renewable energy sources and ESS are connected to the low voltage direct current(LVDC) distribution network through the power conversion system(PCS). Control power is required for the operation of the PCS. In general, controller power is supplied from AC power or DC power through switch mode power supply(SMPS). However, the conventional SMPS has a low input voltage, so development and research on high input voltage self-power suitable for LVDC is insufficient. In this paper, to develop Self-Power that can be used for LVDC, the characteristics of the conventional topology are analyzed, and a series-input single-output flyback converter using a flux-sharing transformer for high voltage is designed. The high input voltage Self-Power was designed in the DCM(discontinuous current mode) to reduce the switching loss and solve the problem of current dissipation. In addition, since it operates even at low input voltage, it can be applied to many applications as well as LVDC. The validity of the proposed high input voltage self-power is verified through experiments.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.3
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• pp.383-390
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• 2018

Piezoelectric micro-machined ultrasonic transducers for highly directional speaker need DC bias voltage. Most existing power amplifiers are not suitable for use in highly directional transducers because they are based on AC. In addition, since the piezoelectric micro-machined ultrasonic transducer has a large capacitive reactance, the power efficiency of the power amplifier is very low. Thus this paper proposes a new high efficiency power amplifier with DC bias voltage. In addition, by designing a matching circuit to compensate the capacitive reactance of the micro-machined ultrasonic transducer, the power efficiency of the power amplifier increases. The operating characteristics of the proposed power amplifier was verified by an experimental prototype. The proposed power amplifier is expected to be widely used in designing and implementing other related power amplifiers.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.495-501
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• 2017

The introduction of smart grid, which is an innovative application of digital processing and communications to the power grid, might lead to more and more cyber threats originated from IT systems. In other words, The Energy Management System (EMS) and other communication networks interact with the power system on a real time basis, so it is important to understand the interaction between two layers to protect the power system from potential cyber threats. This paper aims to identify and clarify the cyber security risks and their interaction with the power system in Smart Grid. In this study, the optimal power flow (OPF) and Power Flow Tracing are used to assess the interaction between the EMS and the power system. Through OPF and Power Flow Tracing based analysis, the physical and economic impacts from potential cyber threats are assessed, and thereby the quantitative risks are measured in a monetary unit.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.10
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• pp.720-725
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• 2013

Power MOSFET operate voltage-driven devices, design to control the large power switching device for power supply, converter, motor control, etc. We have analyzed trench process, field limit ring process for fabrication of unified trench gate power MOSFET. And we have analyzed electrical characteristics of fabricated unified trench gate power MOSFET. The optimal trench process was based on SF6. After we carried out SEM measurement, we obtained superior trench gate and field limit ring process. And we compared electrical characteristics of planar and trench gate unified power MOSFET after completing device fabrication. As a result, the both of them was obtained 500 V breakdown voltage. However trench gate unified power MOSFET was shown improved Vth and on state voltage drop characteristics than planar gate unified power MOSFET.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.1
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• pp.219-226
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• 2016

In this paper, adaptive home power peak-cut control system is developed using PLC. The developed scheme provides monitoring of power usage, power peak-cut control and additional function. In test bed, zone is presented by bedroom, living room, kitchen and bathroom. And individual load is presented by lighting, heater and fan in zone. In developed scheme, zone control is implemented by single PLC modem. And individual load control is implemented by key-map table. In addition, power peak-cut control system S/W, which can perform setting of power peak, power peak-cut control and monitoring of power usage.

• Transactions on Electrical and Electronic Materials
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• v.18 no.5
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• pp.303-309
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• 2017

The flexible AC transmission system (FACTS) provides a new advanced technology solution to improve the flexibility, controllability, and stability of a power system. The unified power flow controller (UPFC) is outstanding for regulating power flow in the FACTS; it can control the real power, reactive power, and node voltage of distribution networks. This paper investigates the performance of the UPFC for power flow control with a series of step changes in rapid succession in a power system steady state and the response of the UPFC to distribution network faults and islanding mode. Simulation was carried out using the MATLAB's simulink sim power systems toolbox. The results, which were carried out on a 5-bus test system and a 4-bus multi-machine electric power system, show clearly the effectiveness and viability of UPFC in rapid response and independent control of the real and reactive power flows and oscillation damping [6].

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1174-1175
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• 2008

A operation scheme to regulate the active power output of the hybrid system consisted of a doubly fed induction generator(DFIG) and a fuel-cell are presented. The power output of the wind turbine fluctuates as the wind speed varies and the slip power between the rotor circuit and power converter varies as the rotor speed change. A fuel cell system can be individually operated and adjusted output power. In this paper, a fuel-cell is performed to regulate the active output power in comparison with the active power output of a DFIG. Based on PSCAD/EMTDC power system tools, we simulated a DFIG and a fuel cell and investigated about dynamics of the output power in hybrid system.

• Journal of Power Electronics
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• v.17 no.5
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• pp.1317-1326
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• 2017

The cascaded H-bridge (CHB) multilevel converter is a promising topology for large-scale photovoltaic (PV) systems. The output voltage over-modulation derived by the inter-module active power imbalance is one of the key issues for CHB PV systems. This paper proposed a dynamic power distribution strategy to eliminate the over-modulation in a CHB PV system by suitably redistributing the reactive power among the inverter modules of the CHB PV system. The proposed strategy can effectively extend the operating region of the CHB PV system with a simple control algorithm and easy implementation. Simulation and experimental results carried out on a seven-level CHB grid-connected PV system are shown to validate the proposed strategy.

• Proceedings of the KIEE Conference
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• summer
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• pp.1263-1265
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• 2004

RF-ID system is one of the very interesting field not only in a technical and economical point of view but also that people are still trying to realize lossless power transmission. This paper has a purpose on the efficient power transmission at the passive type IDcard by using wireless power transmission system. The most difficult but important part of the passive type RF-ID system is building the system that supplies power from Reader-antenna to IDcard-antenna. To check what is the most efficient way to deliver power depending on what kind of specifications of the power-amp in reader, antenna and antenna in IDcard is for operating IDcard circuit efficiently receiving the power from reader-antenna. For this, we used 125kHz sinewave for RF signal as a basic specification, OP-amp for amplifying signal and power-amp for amplifying power, loop type antenna.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1486-1495
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• 2019

Dealing with the DC link fault poses a technical problem for an HVDC based on a modular multilevel converter. The fault suppressing mechanisms of several sub-module topologies with DC fault current blocking capacity are examined in this paper. An improved half-bridge sub-module topology with double direction control switch is also designed to address the additional power consumption problem, and a sub-module topology called hybrid double direction blocking sub module (HDDBSM) is proposed. The DC fault suppression characteristics and sub-module capacitor voltage balance problem is also analyzed, and a self-startup method is designed according to the number of capacitors. The simulation model in PSCAD/EMTDC is built to verify the self-startup process and the DC link fault suppression features.