• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.8
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• pp.1215-1221
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• 2017

Parametric array transducers are used for highly directional speaker in an air environments. Piezoelectric micromachined ultrasonic transducers for parametric array transducers need DC-biased voltage driving signals in order to get high-directional quality-sound features. The existing power amplifier such as class A amplifiers has low efficiency and require large volume heatsinks. To overcome the above-mentioned disadvantages of the conventional amplifier, this paper proposes a new power amplifier system. The proposed power amplifier system ensures high linearity of output characteristic by utilizing the push-pull class B type amplifier. Furthermore, the proposed power amplifier system gets high efficiency because it contains the DC-DC converter-type power supply which can perform energy recovery and envelope tracking function. Also the paper suggests the detailed circuit topology. Its characteristics are verified by the detailed experimental results.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.6
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• pp.707-714
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• 2022

Hydrogen production using solid oxide electrolysis cells (SOEC) is a promising technology because of its efficiency, cleanness, and scalability. Especially, high-power SOEC system has received a lot of attention from researchers. This study compared and analyzed the low-power and high-power SOEC system in term of economic. By using revenue requirement method, levelized cost of hydrogen (LCOH) was calculated for comparison. In addition, the sensitivity analysis was performed to determine the dependence of hydrogen cost on input variables. The results indicated that high-power SOEC system is superior to a low-power SOEC system. In the capital cost, the stack cost is dominant in both systems, but the electricity cost is the most contributed factor to the hydrogen cost. If the high-power SOEC system combines with a nuclear power plant, the hydrogen cost can reach 3.65 $/kg when the electricity cost is 3.28 ¢/kWh and the stack cost is assumed to be 574 $/kW.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.982-986
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• 1996

The development of a high power BLDC servo system for a control of the large scale mechanical system is presented. Using DSP TMS320C30, a control unit which is suitable for motor drive system, is developed. Also, based on the developed control unit, BLDC drive system for the speed control is constructed. The algorithms of the vector control, current control, and speed control is implemented using TMS320C30 Software Development Tool. The developed high power BLDC motor drive system is applied to the large scale mechanical system and its feasibility is verified through the experimental results.

• Journal of Power Electronics
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• v.11 no.4
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• pp.551-560
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• 2011

This paper proposes a grid-tied power conditioning system for the fuel cell power generation, which consists of a 2-stage DC-DC converter and a 3-phase PWM inverter. The 2-stage DC-DC converter boosts the fuel cell stack voltage of 26-48V up to 400V, using a hard-switching boost converter and a high-frequency unregulated LLC resonant converter. The operation of the proposed power conditioning system was verified through simulations with PSCAD/EMTDC software. Based on the simulation results, a laboratory experimental set-up was built with a 1.2kW PEM fuel-cell stack to verify the feasibility of hardware implementation. The developed power conditioning system shows a high efficiency of 91%, which is a very positive result for the commercialization.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.3
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• pp.117-124
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• 2007

This paper is about the Extra-High voltage distribution system in the customer's area. The power loss in the distribution system in the customer's area is disregarded and rarely managed so far. But, economically, this loss is not small quality to ignore. So, in this paper, we calculate the power loss of the Extra-High voltage distribution system in the customer's area by changing the locations of power transformer and other power facilities to decrease power loss in decreased secondary line length. And we also show the payback time of the proposed Extra-High voltage distribution system in the customer's area by simplified calculations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.6
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• pp.738-745
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• 2014

Recently, various measures have been discussed for overcoming depletion of fossil fuels and environmental pollution. One of the measures is electric vehicles. But electric vehicles has some limitations from high cost of battery and low efficiency, so operation distance of electric cars is limited. Also there are difficulties that charging lines should be connected by an electric car whenever it charges. Thus, many studies have been conducted to overcome the limitation using conventional batteries of electric vehicles. As a result, the OLEV(On-Line Electric Vehicle) was developed. But the OLEV system is some limitations. The OLEV system causes power quality problems when it charges. Power quality problem cannot be ignored because OLEV systems are closely connected by distribution grids. In this paper, the OLEV system is designed by using PSCAD/EMTDC, and the power quality is measured and evaluated. Power quality is divided by two cases; harmonics and high-frequency. Harmonics were evaluated according to IEEE Std. 519-1992. But the evaluation of High-frequency could not take it because there was no standard. For this reason, the data measured by OLEV system was compared with the EN50065 regulation.

• Journal of Power Electronics
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• v.8 no.4
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• pp.332-344
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• 2008

High frequency AC (HFAC) power distribution systems delivering power through a high frequency AC link with sinusoidal voltage have the advantages of simple structure and high efficiency. In a multiple module system, where multiple resonant inverters are paralleled to the high frequency AC bus through connection inductors, it is necessary for the output voltage phase angles of the inverters be controlled so that the circulating current among the inverters be minimized. However, the phase angle of the resonant inverters output voltage can not be controlled with conventional phase shift modulation or pulse width modulation. The phase angle is a function of both the phase of the gating signals and the impedance of the resonant tank. In this paper, we proposed a pulse phase modulation (PPM) concept for the resonant inverters, so that the phase angle of the output voltage can be regulated. The PPM can be used to minimize the circulating current between the resonant inverters. The mechanisms of the phase angle control and the PPM were explained. The small signal model of a PPM controlled half-bridge resonant inverter was analyzed. The concept was verified in a half bridge resonant inverter with a series-parallel resonant tank. An HFAC power distribution system with two resonant inverters connected in parallel to a 500kHz, 28V AC bus was presented to demonstrate the applicability of the concept in a high frequency power distribution system.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.291-300
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• 1999

Currently under development is an airborne auxiliary power unit with 100 Kw equivalent power, which is composed of a centrifugal compressor, a reverse annular combustor, and a radial turbine. Air-foil bearings are used in this power unit to eliminate the oil supplying system, which can reduce the system complexity and weight. The high speed generator is adopted as an electric power generation and engine starting system, which can also eliminate the reduction gear system. Not only electric power but also pneumatic power is provided by bleeding the compressed air This power unit is aimed for the multi-purpose use such as a primary power unit In the army weapon system, an auxiliary power and environmental control unit in a next-generation tank, and a smoke generating unit.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.481-484
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• 2006

A electric power conversion system in a pumped storage power plant is important equipment for converting electric motor kinetic energy into electric power. A electric power conversion monitoring system consists of high voltage thyristor firing equipment, fault detection module, data gathering module, real time data processing equipment and man machine interface system. This paper describes electric power conversion system overview, the developed SFC monitoring system configuration including system characteristics, and successful application result to San-Cheong pumped storage power plant.

• 전기의세계
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• v.24 no.2
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• pp.71-77
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• 1975

This paper describes the results of a study for the stability of power system when the Kori Nuclear #1 P/P is operated with existing system. First, a transient disturbance, which effects the stability of entire power system, was analysed and to cope with the problem a load shedding method was studied to recover the fluctuation of the power system. Second, transient stability problem was studied when three phase fault occurs in 345 Extra High Voltage power System, and from this result, it was found to be highly effective that high speed protecting device should be provided and operated to recover the fault.