• Journal of Power Electronics
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• v.12 no.3
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• pp.387-398
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• 2012

It is known that transformer based power supplies for ozone generators have low efficiency, high cost and exhibits a limited frequency range of operation. To overcome these disadvantages, this paper proposes a high frequency ozone generator with the absence of a transformer. The voltage step-up is achieved only by utilizing the resonant tank. This is made possible by a novel combination of ozone chamber materials that allow ozone to be generated at only 1.5 - 3.5 $kV_{p-p}$. The input to the resonant tank is driven by a PWM full bridge resonant inverter. Furthermore, zero-current zero-voltage switching (ZCZVS) operation is achieved by employing a duty factor of 25% between the switches of the full bridge. The advantages of the proposed system include high efficiency, low cost and the ability to control ozone production by varying the input voltage to the inverter. The prototype is verified by both simulation and experimental results.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.345-352
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• 2017

In this paper, a non-dissipative snubber for reducing the switching losses in the step down converter is proposed. The conventional step down converter, e.g., buck converter, suffers from serious switching losses and consequentially heat generation because of its hard switching. Thus, it is unsuitable for high switching frequency operation. Reduction of the reactive components' size, such as an output inductor and capacitor, is difficult. The proposed snubber can slow down the increasing current slopes and switch voltage at turn-on and turn-off transients, thereby significantly reducing the switching loses. Additionally, the slowly increasing current during switch turn-on transition, can effectively solve the output rectifier diode reverse recovery problem. Therefore, the proposed non-dissipative snubber not only leads to the efficiency of converter operation at high switching frequency but also reduces the reactive components size in proportion to the switching frequency. To confirm the validity of the proposed circuit, theoretical analysis and experimental results from a 150 W, 1 MHz prototype are presented.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.443-445
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• 1995

Since the residential load is an AC load, while the output of solar cell is a DC power, the photovoltaic system needs the DC/AC converter to utilize solar cell and must provide the sinusoidal wave current and voltage with unity power factor in the case of driving to Interact with utility line. It is always necessary for the output of solar cell to operate in the vicinity of maximum power point, since it is greatly fluctuated by insolation. This paper treats that we will constitute a single phase PWM voltage source inverter and trace the modulation index which always maximize the output of solar cell in propotion to insolation variation and prove it by simulation that we can provide current wave, which is nearly sinusoidal wave with unity power factor, for load and utility line.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1366-1379
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• 2019

High-gain DC/DC converters have become one of the key technologies for the grid-connected operation of new energy power generation, and its research provides a significant impetus for the rapid development of new energy power generation. Inspired by the transformer effect and the ripple-suppressed ability of a coupled inductor, a double-coupled inductor high gain DC/DC converter with a ripple absorption circuit is proposed in this paper. By integrating the diode-capacitor voltage multiplying unit into the quadratic Boost converter and assembling the independent inductor into the magnetic core of structure coupled inductors, the adjustable range of the voltage gain can be effectively extended and the limit on duty ratio can be avoided. In addition, the volume of the magnetic element can be reduced. Very small ripples of input current can be obtained by the ripple absorption circuit, which is composed of an auxiliary inductor and a capacitor. The leakage inductance loss can be recovered to the load in a switching period, and the switching-off voltage spikes caused by leakage inductance can be suppressed by absorption in the diode-capacitor voltage multiplying unit. On the basis of the theoretical analysis, the feasibility of the proposed converter is verified by test results obtained by simulations and an experimental prototype.

• Environmental Engineering Research
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• v.25 no.2
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• pp.238-242
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• 2020

Sediment microbial fuel cells (SMFCs) illustrated great potential for powering environmental sensors and bioremediation of sediments. In the present study, array anodes for SMFCs were fabricated with graphite rods as anode material and stainless steel plate as electric current collector to make it inconvenient to in situ settle down and not feasible for large-scale application. The results demonstrated that maximum power of 89.4 ㎼ was obtained from three graphite rods, twice of 43.3 ㎼ for two graphite rods. Electrochemical impedance spectroscopy revealed that three graphite rods resulted in anodic resistance of 61.2 Ω, relative to 76.0 Ω of two graphite rods. It was probably caused by the parallel connection of the graphite rods, as well as more biomass which could reduce the charge transfer resistance of the biofilm anode. The presently designed array configuration possesses the advantages of easy to enlarge the surface area, decrease in anodic resistance because of the parallel connection of each graphite rod, and convenience to berry into sediment by gravity. Therefore, the as prepared array node would be an effective method to fabricate large-scale SMFC and make it easy to in situ applicate in natural sediments.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.11
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• pp.1503-1510
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• 2014

This study organizes scenarios on the power supply plans and electricity load forecasts considering their uncertainties and estimates natural gas quantity for electricity generation, total electricity supply cost and air pollutant emission of each scenario. Also the analysis is performed to check the properness of government's natural gas demand forecast and the possibility of achieving the government's CO2 emission target with the current plan and other scenarios. In result, no scenario satisfies the government's CO2 emission target and the natural gas demand could be doubled to the government's forecast. As under-forecast of natural gas demand has caused the increased natural gas procurement cost, it is required to consider uncertainties of power plant construction plan and electricity demand forecast in forecasting the natural gas demand. In addition, it is found that CO2 emission target could be achieved by enlarging natural gas use and demand-side management without big increase of total costs.

• Tunnel and Underground Space
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• v.23 no.6
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• pp.506-520
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• 2013

While geothermal energy provides the only base-load power among renewable energy sources, its development has been carried out predominantly in volcanic area. EGS (Enhanced Geothermal System) is a ubiquitous technology that can allow the geothermal power generation virtually in any area. This manuscript introduces the current state-of-the-art of EGS development in the world and presents the hydraulic stimulation technology and associated microseismicity which are key technical component in EGS. Finally this paper suggests the key research areas required in Korea for further development of EGS.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.129-134
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• 2012

In this paper, speed control of IPMSM drives for the next generation domestic high speed railway system using NPC 3-level inverters is presented. The NPC multilevel inverter is suitable for the high-voltage and high-power motor drive system because it has advantages in that the voltage rating of the power semiconductor devices and output current harmonics are reduced. For the speed control of IPMSM using NPC 3-level inverters, maximum torque control is applied in the constant torque region, and filed weakening control is applied in the constant power region. Simulation programs based on MATLAB/Simulink are developed. Finally the designed system is verified and their characteristics are analyzed by the simulation results.

• Proceedings of the KIPE Conference
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• 2008.10a
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• pp.206-208
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• 2008

In this paper, the two-stage DC-DC converter is proposed to make the control simple and to boost the low input voltage in the fuel cell generating system. The low efficiency of the conventional power converter is caused by a characteristic of the low-voltage and high-current in the fuel cell generating system. High-frequency transformer is needed to block the noise and to guarantee the safety of cell and load as a magnetically insulation. The proposed two-stage DC-DC converter for a fuel cell generation is more efficient than the traditional one-stage converter and easy to control. The design of a high-frequency transformer is also simple. Finally, the utility of the proposed converter is proved by the simulations and experiments.

• Transactions on Electrical and Electronic Materials
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• v.15 no.5
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• pp.279-283
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• 2014

In this paper, we present an economical and practical standard to install a bypass diode in a thin-film PV module. This method helps to reduce heat generation and to prevent module degradation due to excess current from reverse bias. The experimental results confirm that for different numbers of solar cells, there is a relation between the excess reverse current and the degradation of solar cells in a-Si:H modules. The optimal number of solar cells that can be connected per bypass diode could be obtained through an analysis of the results to effectively suppress the degradation and to reduce the heat generated by the module. This technique could be expanded for use in high power crystalline Si PV modules.