• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.9
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• pp.973-983
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• 1992

A very fast algorithm, using fast Haar transformation with half a cycle dc-offset free data, to extract the power frequency components and to detect faults in power systems is proposed. For the speed-up, two important techniques are used. First, according to the symmetric characteristics of sine and cosine functions, fundamental frequency components are calculated with only half a cycle sample data. For using these characteristics, post-fault de-offset components must be removed beforehand. Therefore, secondly, a newly designed digital filter is used to remove exponentially decaying dc-offset from the post-fault signal. In accordance with series simulations, transmission line faults can be detected in around half a cycle after faults.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.10
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• pp.618-624
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• 2004

In this paper, a new controller for a single-phase PWM converter is described, which requires only two input parameters, the dc voltage and the ac current. Detail simulation model with EMTDC(Electro-Magnetic Transient program for DC transmission) including power circuit and controller was developed to verify the operation of proposed controller. The application feasibility of the proposed controller was verified through experimental works with a prototype. The proposed controller has a simple structure in the point of hardware implementation, and shows excellent performance in normal operation as well as in sudden load change.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.254-255
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• 2017

공진형 컨버터에서 일반적으로 소프트 스위칭과 같은 조건을 만족시키기 위해 주파수 제어를 많이 사용한다. 그러나 전계결합형 무선전력전송 시스템 특성상 이격 거리나 정렬 오차 정도 따라 송 수신부를 연결하는 링크 캐패시턴스 값이 민감하게 변한다. 이런 시스템에서는 공진 주파수 추종과 동시에 시비율 제어가 필요하다. 송신부 앞 또는 부하단에 dc/dc컨버터를 추가하는 2단 구성은 시스템 효율이 1단 구성에 비해 낮다는 단점이 있다. 따라서 본 논문에서는 무선전력전송 시스템에 비대칭 하프 브릿지를 사용하여 시비율 제어와 주파수 추종제어를 할 수 있는 구조를 제안한다. 이는 시뮬레이션을 이용하여 검증한다.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.594-600
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• 2017

HVDC transmission systems can be configured in many ways to take into account cost, flexibility and operational requirements. [1] For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance of each cycle. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be warranted, due to other benefits of direct current links. HVDC allows power transmission between unsynchronized AC transmission systems. Since the power flow through an HVDC link can be controlled independently of the phase angle between the source and the load, it can stabilize a network against disturbances due to rapid changes in power. HVDC also allows the transfer of power between grid systems running at different frequencies, such as 50 Hz and 60 Hz. This improves the stability and economy of each grid, by allowing the exchange of power between incompatible networks. This paper proposed to establish Korean HVDC technology through a cooperative agreement between KEPCO and LSIS in 2010. During the first stage (2012), a design of the ${\pm}80kV$ 60MW HVDC bipole system was created by both KEPCO and LSIS. The HVDC system was constructed and an operation test was completed in December 2012. During the second stage, the pole#2 system was fully replaced with components that LSIS had recently developed. LSIS also successfully completed the operation test. (2014.3)

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.1056-1058
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• 1998

Voltage dips caused by transmission system faults are usually of a short duration. High speed relaying and breaker operation will typically limit the disturbance to 0.1 seconds. Most motor controllers obtain their control power directly from the bus by means of a control transformer. Under this condition, a voltage dip can cause the contactor to drop out. disconnecting the motor from the line. The rapid re-energizing of the controller is in effect a fast reclosure which may result in motor damage. The time delay re-energizing of controller will result in a greater loss of speed and possibly loss of stability. Other means of controller can be used to prevent the motor from being disconnected from line during the fault. This can be accomplished by DC power controller or mechanically latched controller. This paper demonstrates that DC power controller or mechanically latched type controller to prevent the motor from being disconnected from line during the fault is, the most effective in minimizing speed reduction, transient motor current, transient motor torque and transient shaft torque by EMTP calculation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.144-144
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• 2007

Effects of power ratio on the electrical and optical properties of Au based Ga-, B- codoped ZnO(GZOB) thin films were investigated. GZOB thin films on Au based PC flexible substrate were deposited at various power in the range from 50 to 125 W by DC magnetron sputtering. Au layer was fabricated to achieve good electrical conductivity. The presence of additional boron impurity leads to improve structural defects. Thus, the c-axis orientation along (002) plane was enhanced with the increasing of power ratio and the surface morphology of the films showed a homogeneous and nano-sized microstructure. GZOB films grown at 125W were investigated a low resistivity value of $1{\times}10^{-3}{\Omega}cm$ and a visible transmission of 80% with a thickness of 300nm.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.4
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• pp.34-42
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• 2012

In this paper, a wide-input range CMOS multi-mode rectifier for wireless power transfer system is presented. The output voltage of multi-mode rectifier is sensed by comparator and switches are controlled based on it. The mode of multi-mode rectifier is automatically selected by the switches among full-wave rectifier, 1-stage voltage multiplier and 2-stage voltage multiplier. In full-wave rectifier mode, the rectified output DC voltage ranges from 9 V to 19 V for a input AC voltage from 10 V to 20 V. However, the input-range of the multi-mode rectifier is more improved than that of the conventional full-wave rectifier by 5V, so the rectified output DC voltage ranges from 7.5 V to 19 V for a input AC voltage from 5 V to 20 V. The power conversion efficiency of the multi-mode rectifier is 94 % in full-wave rectifier mode. The proposed multi-mode rectifier is fabricated in a $0.35{\mu}m$ CMOS process with an active area of $2500{\mu}m{\times}1750{\mu}m$.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.486-488
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• 1996

A dc-dc converter which transfers l2-48W of power(regulated output voltage 24V) across a large, variable air gap(1-2cm) has been designed. This converter employs double resonance to compensate the large leakage inductance of the primary and secondary of the transcutaneous transformer. To maximize the effect of resonance, a constant frequency, duty cycle control method is used. The duty cycle control presents advantages over a frequency control in terms of increase in dc voltage gain and reduction of the primary current. The analysis and design procedure for the proposed scheme is presented and the performance result is simulated and verified experimentally.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.219-221
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• 2005

Various adjustment devices which present automobile uses electric motion motor of reducer built-in type for user's convenience are increasing. The example are seat control motor, sunroof motor, power windows motor etc. To get low noise, high effectiveness special quality in automobile DC motor of reducer built-in type, reducer department's transmission efficiency and noise, vibration quality are very important. The reducer used to DC motor of automobile reducer built-in type use worm gear for enough torque and proper number of rotation. We need optimization design technology of deceleration module including worm gear and housing for reducer development that have special quality of good quality.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.255-258
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• 1999

We investigated the current limiting characteristics of resistive and inductive SFCLs with 100 $\Omega$ of quench impedance for a single line-to-ground fault. which accounts for about 70% of the total power line faults, in the 154 kV transmission system. The fault simulation at the phase angles 0$^{\circ}$, 45$^{\circ}$, and 90$^{\circ}$ showed that the resistive SFCL limited the fault current less than 15 kA without any DC component after one half cycle from the instant of the fault. On the other hand, the inductive SFCL suppressed the current below 12 KA, but with 3 kA of DC component which decreased to zero in 5 cycles. We concluded that the inductive SFCL had higher performance in current limiting but the resistive SFCL was better from the view point of DC components.