• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.9 s.351
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• pp.23-30
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• 2006

This paper presents a design of a high-efficiency CMOS DC-DC boost converter using a current-sensing feedback method. High-precision current-sensing circuity is incorporated in order to sense the current flowing in the inductor, which determines the switching scheme of the pulse-width modulation. The external components or large chip area for the frequency compensation can be avoided while maintaining the stable operations of the converter. Various input/output voltage levels can be available through the external resistor strings. The designed DC-DC converter is fabricated in a 0.18-um CMOS technology with a thick-gate oxide option. The converter shows the maximum efficiency over 90% for the output voltage of 3.3V and load current larger than 200mA. The load regulation is 1.15% for the load current change of 100mA.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.8
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• pp.23-31
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• 2015

This paper proposes an advanced distance relaying based on the DC offset removal filter to minimize the effects of DC offset on a double circuit transmission line. The proposed DC offset removal filter uses only one cycle of data for phasor extraction computation, which does not need to preset the time constant of the DC offset component. This proposed distance relaying uses not only the residual current of the faulted circuit but also mutual current of the healthy adjacent circuit. A series of off-line test results using ATP simulation data show the effectiveness of the an advanced distance relaying.

• Journal of IKEEE
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• v.23 no.4
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• pp.1140-1149
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• 2019

In general, there are various pulse width modulation(PWM) methods simply using the offset voltage injection in voltage source converter(VSC). In accordance with the AC side voltage synthesis method with the offset voltage, DC side voltage utilization factor in VSC is changed. Also, this can apply equally to the MMC system. In other words, if the DC side capacity of the high voltage DC(HVDC) transmission system is determined, the maximum reactive power which can be supplied to the AC side can be changed according to the applied output voltage synthesis method with the offset voltage. In this paper, the leg energy pulsation in MMC system according to the AC side output voltage synthesis method with offset voltage which several representative PWM are applied to are mathematically analyzed and compared with each other. Finally, the above results are verified by simulation emulating the 400MVA full-scale MMC system to determine the consistency of the mathematical analysis.

• Progress in Superconductivity and Cryogenics
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• v.23 no.3
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• pp.51-54
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• 2021

The DC system has less power loss compared to the AC system because there is no influence of frequency and dielectric loss. However, the zero-crossing point of the current is not detected in the event of a short circuit fault, and it is difficult to interruption due to the large fault current that occurs during the opening, so the reliability of the DC breaker is required. As a solution to this, an LC resonance DC circuit breaker combined a superconducting element has been proposed. This is a method of limiting the fault current, which rises rapidly in case of a short circuit fault, with the quench resistance of the superconducting element, and interruption the fault current passing through the zero-crossing point through LC resonance. The superconducting current limiting element combined to the DC circuit breaker plays an important role in reducing the electrical burden of the circuit breaker. However, at the beginning of a short circuit fault, superconducting devices also have a large electrical burden due to large fault currents, which can destroy the element. In this paper, the reactor is connected to the source side of the circuit using PSCAD/EMTDC. After that, the change of the fault current according to the reactor capacity and the electrical burden of the superconducting element were confirmed through simulation. As a result, it was confirmed that the interruption time was delayed as the capacity of the reactor connected to the source side increased, but peak of the fault current decreased, the zero-crossing point generation time was shortened, and the electrical burden of the superconducting element decreased.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.1
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• pp.31-37
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• 2015

This paper proposes a 3.3-kW bi-directional EV charger with V2G and V2H functions. The bi-directional EV charger consists of a DC-DC converter and a DC-AC inverter. The proposed EV charger is suitable for wide battery voltage control due to the two-stage configuration of the DC-DC converter. By employing a fixed-frequency series loaded resonant converter as the isolated DC-DC converter, zero-current-switching can be achieved regardless of battery voltage variation, load variation, and power flow. A 3.3-kW prototype of the proposed EV charger has been built and verified with experiments, and indicates a maximum efficiency of 94.39% and rated efficiency of 94.23%.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.6
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• pp.16-23
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• 2003

In this paper, we propose an efficient bias circuit of discrete BJT component for hearing aid. The collector feedback bias circuit, widely used for the hearing aid, has a resistor for negative feedback. As the resistor affects AC and DC simultaneously, it is quite difficult to adjust amplifier gain without changing DC bias point. The previous bias circuit also has weak point to be oscillated by the positive feedback of power noise if gain of hearing aid is high. In the proposed circuit, we can reduce the two weak points of the previous circuit by adding a resistor to the collector feedback bias circuit between base and power supply which is $\beta$ times target than the collector resistor. Thus. we can change amplifier gain without changing DC bias point, and reduce power noise gain about 18.5% compare to that of tile previous circuit in the simulation.

• Journal of the Korean Society of Safety
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• v.25 no.2
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• pp.18-23
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• 2010

This paper describes a cause of fire accidents on power system fire DC electric traction vehicles. We investigated fire scene of power line for DC electric traction vehicles. From analysis results, the cause of fire on power line turned out line to ground fault between a feeder of electric power services(pantagraph) and DC electric traction vehicle roof. Fire accident of DC electric traction vehicles be assumed that electric sparks had been produced between the pantagraph and the power line conductor by repetitively making contact and separation, maybe if some material like branches get in between connecting rod it makes progress line to ground fault. ZnO arresters are widely used to protect DC electric traction vehicles against overvoltages caused by lightning or switching surges. However, the arresters are deteriorated by commercial overvoltages and/or lightning one. The deteriorated arresters could lead power failures, such as line to ground fault by a thermal runaway resulting from the increases in leakage current even in a nominal power system voltage. Finally, the power failures would be causative of the fire accident.

• KIPE Magazine
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• v.23 no.4
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• pp.30-37
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• 2018

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2003.10a
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• pp.22-23
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• 2003

• 전기의세계
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• v.66 no.11
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• pp.19-23
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• 2017