• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2004년도 춘계학술대회 논문집
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• pp.100-103
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• 2004

This paper presents the aspect and distribution of voltage and current harmonics being made at low voltage power systems. The voltage and current harmonics in power systems supplying various loads were monitored and analyzed. We have examined the results compared to advanced countries' harmonics control standards. As a result, the current harmonics were significantly greater than the voltage harmonics. In particular, the harmonics of currents flowing through loads with power switching electronics was pronounced. Also, the contents of current harmonics of street lamp circuits was about 30%, and it was decreased to 12.3% with the installation of series reactor. On the whole, The measured results of voltage and current harmonics exceeds the regulation limits recommended by IEEE 519-1992.

• 전력전자학회논문지
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• 제25권1호
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• pp.68-71
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• 2020

As a T-type three-level PWM converter has several intrinsic advantages, it has been widely studied for many applications. However, it requires an additional voltage control loop for balancing each DC link voltage. Generally, satisfying this requirement involves the use of an offset voltage to provide a neutral point current without affecting other variables, such as the total DC link voltage and three-phase input current. In this study, the theoretical relationship between the offset voltage and the neutral point current is analyzed. The results can be beneficial for effective voltage balancing controller design. The effectiveness of the analytical modeling is verified by simulation and experimental results.

• Journal of Multimedia Information System
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• 제5권2호
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• pp.139-142
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• 2018

This work presents a novel architecture of phase locked loop (PLL) with the current compensating scheme to improve phase noise characteristic. The proposed PLL has two charge pumps (CP), main-CP (MCP) and sub-CP (SCP). The smaller SCP current with same time duration but opposite direction of UP/DN MCP current is injected to the loop filter (LF). It suppresses the voltage fluctuation of LF. The PLL has a novel voltage controlled oscillator (VCO) consisting of a voltage controlled resistor (VCR) and the three-stage ring oscillator with latch type delay cells. The VCR linearly converts voltage into current, and the latch type delay cell has short active on-time of transistors. As a result, it improves phase noise characteristic. The proposed PLL has been fabricated with $0.35{\mu}m$ 3.3 V CMOS process. Measured phase noise at 1 MHz offset is -103 dBc/Hz resulting in 3 dBc/Hz phase noise improvement compared to the conventional PLL.

• 한국초전도ㆍ저온공학회논문지
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• 제11권4호
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• pp.25-28
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• 2009

In order to apply superconducting electric machineries such as a Superconducting Fault Current Limiter (SFCL) to the power grid, the single module should be connected in series to have reasonable size. Superconducting tapes in the module also should be stacked to satisfy requirements such as large operation current of the power grid. This is because a single superconducting tape has restricted applicable current capacity. Moreover especially in SFCL at the fault, there should be equal voltage distribution in series-connected SFCL modules. In this paper, we investigated the voltage distribution in fault current of series-connected YBCO coated conductors (CC). Depending on characteristics of the CC samples such as critical current, even voltage distribution could be achieved or not. In addition, the effect of stacked CC on the change of voltage distribution comparing to non-stack cases in series connection was confirmed by experiments. As the CC stacked, voltage difference could be reduced.

• 조명전기설비학회논문지
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• 제28권2호
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• pp.60-69
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• 2014

This paper proposed the circulation current control scheme in the single phase inverter system. The load experiment of the power conversion system including the UPS usually uses the passive components such as resistors and inductors. Therefore, the energy consumption is serious problem. In addition, the system is out of order when it is installed in the local area, and the load experiment can not perform adequately after troubleshooting, because there is no the load equipment, and the power capacity is not enough in the local area. The paper does the research on the circulation current control scheme, it does not need the load equipment, and the load current can reuse as the input current of the equipment. Instead of the conventional method the voltage-voltage and voltage-current control scheme introduced the parallel converter concept is newly proposed, and the validity of the proposed control scheme is investigated by both simulation and experimental results.

• 한국전기전자재료학회논문지
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• 제24권2호
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• pp.141-146
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• 2011

When the current of the superconducting element exceeds its critical current by the fault occurrence, the quench of the high-$T_C$ superconducting fault current limiter (HTSC) comprising the flux-lock type superconducting fault current limiter (SFCL) occurs. Simultaneously, the magnetic flux in the iron core induces the voltage in each coil, which contributes to limit the fault current. In this paper, the fault current limiting characteristics of the flux-lock type SFCL as well as the load voltage sag suppressing characteristics according to the flux-lock type SFCL's winding direction were investigated. To confirm the fault current limiting and the voltage sag suppressing characteristics of the this SFCL, the short-circuit tests for the simulated power system with the flux-lock type SFCL were carried out. The flux-lock type SFCL designed with the additive polarity winding was shown to perform more effective fault current limiting and load voltage sag suppressing operations through the fast quench occurrence right after the fault occurs and the fast recovery operation after the fault removes than the flux-lock type SFCL designed with the subtractive polarity winding.

• 전기학회논문지P
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• 제59권4호
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• pp.473-476
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• 2010

In this paper, we analyzed the short circuit current of a low voltage direct current distribution system. For the analysis, we performed the modeling of the low voltage direct current distribution system with a 6-pulse three-phase thyristor rectifier using the PSCAD/EMTDC, surveyed impedance of sources, transformers and distribution lines to run a simulation. A result of the simulation is that short circuit currents of the direct current distribution system with the rectifier decreased due to a thyristor-ON-resistance(Ron). But in case of the low thyristor-ON resistance, output fault current of the rectifier increased over three-phase short circuit current of an AC power system without a rectifier by regular ratio of the rectifier. Because the output fault current of the rectifier can increase over interrupting the capacity of circuit breakers, studying short circuit currents of a low voltage direct current distribution system with a rectifier is necessary for introducing the direct current distribution systems.

• 한국정보통신학회논문지
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• 제11권5호
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• pp.955-960
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• 2007

본 연구에서는 단채널효과를 감소시키기 위하여 개발되고 있는 이중게이트 MOSFET의 게이트인가 전압에 따른 터널링전류의 변화를 관찰하고자한다. 소자가 나노단위까지 스케일링되면서 터널링전류는 매우 중요한 전류요소가 되었으며 특히 차단전류를 구성하고 있는 열방사전류와 비교하면 소자의 크기가 미세해질수록 급격히 증가하는 특성을 보이고 있다. 이를 감소시키기 위한 연구가 활발히 진행되고 있으며 본 연구에서는 이에 부응하기 위하여 게이트 인가전압에 따른 터널링전류의 변화를 고찰할 것이다. 게이트전압에 대한 터널링전류 변화를 관찰하기 위하여 전위분포함수를 유도하였으며 전위분포함수와 터널링확률의 관계로부터 차단전류변화를 유도하였다. 이와같이 유도한 전류는 열방사전류와 비교되었으며 터널링전류 감소를 위한 유효게이트전압에 대한 관계를 유도하였다.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.193-195
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• 2003

In superconductor power systems, a quench detector can misrecognize oscillation about current or voltage control as a quench. So, for the correct detection of a quench, it seems need to guarantee a smooth control of current or voltage. In this paper, we have studied a control function and control parameter for smooth control of current or voltage.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1678-1680
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• 1997

The pulsed power with the high voltage and current can be used to the fields of high speed pulses of energy in different forms such as electric current and voltage, electron beam, ion beam, x-rays, gamma rays, heat, magnetics fields, sound and shock waves. This paper is directed mainly at electrical engineers working on production and practical application of high speed pulsed power with high voltage and current.