• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2013년도 추계학술대회
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• pp.215-218
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• 2013

본 논문은 낙뢰 Surge 방호를 위하여 독립접지를 공통접지로 개선하는 효율적인 방법을 제안하였다. 낙뢰 Surge 방호를 위해서는 등전위 이론에 근거하는 공통접지방식이 적합하고, 중성선이 있는 전원계통에서는 공통접지방식을 사용하는 것이 국제적으로 통용되는 기술규격이다. 따라서 낙뢰 Surge에 취약한 문제점을 갖고 있는 기존의 중성선이 없는 전원계통의 독립접지방식을 중성선이 있는 전원계통의 공통접지방식으로 개선을 하고, 정전압소자를 이용하여 낙뢰 Surge를 방호하는 효율적인 등전위 시스템 구축 방법을 제안한다.

• 전기학회논문지
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• 제60권7호
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• pp.1438-1443
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• 2011

The increase of power capacity in the superconducting fault current limiter (SFCL) is essential for application into the power grid. To achieve this, when superconducting units were connected in series and parallel, the unbalanced quenching characteristics between superconducting units generated by different critical current behavior should be improved. In the transformer-type SFCL, the superconducting units connected in series could be simultaneously quenched by the connection of neutral lines between secondary coils and superconducting units. From this the consumed power in superconducting units was equally distributed. In addition, the more the turn ratio of the transformer was reduced, the more consumed power in the superconducting units was reduced by the decrease of the induction voltage generated in the superconducting units. From those results, the transformer-type SFCL using neutral lines could increase the power capacity of the SFCL by the equal power division into the superconducting units.

• 전력전자학회논문지
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• 제22권4호
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• pp.285-296
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• 2017

This paper proposes an improved modulation scheme for the medium voltage modular multi-level converter (MMC), which operates in the nearest level control and applies in the medium voltage direct current (MVDC) system. In the proposed modulation scheme, the offset (neutral-to-zero output) voltage is adjusted, with the phase voltage magnitude, thereby maintaining a constant value with N+1 level in the controllable modulation index (MI) range. In order to confirm the proposed scheme's validity, computer simulations for the 22.9 kV - 25 MVA MMC were performed with PSCAD/EMTDC, as well as hardware experiments for the 380 V - 10 kVA MMC. The proposed modulation scheme offers to build a constant pole voltage regardless of the MI value, and to build a phase voltage with improved total harmonic distortion (THD).

• 전기학회논문지
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• 제65권2호
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• pp.311-318
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• 2016

This paper is a study on the neutral point voltage balancing of the three-phase 3-level T-type inverter using the predictive control techniques. Recently, multi-level inverter has been attracting attention as the advantages such as efficiency improving and harmonic reduction. Especially, the T-type inverter topology is advantageous in low DC-link voltage. However, in case of the prediction control, it takes a lot of time, because there exist 27 voltage vectors and it has to be calculated according to the respective voltage vectors. Therefore, in this paper, we propose a method to implement predictive control techniques while reducing the operation time. In order to reduce the operation time, the predictive control is implemented by using the minimum voltage vector except for the unnecessary voltage vector. The result of the implemented predictive control is added to the SPWM by using the offset voltage. It was verified through simulation and experimental results.

• Journal of Power Electronics
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• 제17권4호
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• pp.923-932
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• 2017

This paper proposes a novel scheme which can compensate the common-mode voltage (CMV) for five-level active neutralpoint clamped (5L-ANPC) inverters, which is based on modifying the space vector pulse width modulation (SVPWM) and adding an auxiliary leg to the inverter. For the modified SVPWM, only the 55 voltage vectors producing low CMV values among the 125 possible voltage vectors are utilized, which varies over the three voltage levels of $-V_{dc}/12$, 0 V, and $V_{dc}/12$. In addition, the compensating voltage, which is injected into the 5L-ANPC inverter system to cancel the remaining CVM through a common-mode transformer (CMT) is generated by the additional NPC leg. By the proposed method, the CMV of the inverter is fully eliminated, while the utilization of the DC-link voltage is not decreased at all. Furthermore, all of the DC-link and flying capacitor voltages of the inverter are well controlled. Simulation and experimental results have verified the validity of the proposed scheme.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 전력전자학술대회 논문집
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• pp.707-710
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• 2002

A 120kV/70A high voltage switch has been installed at Korea Atomic Energy Research Institute in Taejon to supply power with Korea Superconducting Tokamak Advanced Research (KSTAR) Neutral Beam Injection (NBI) system. NBI system requires fast cutoff of the power supply voltage for protection of the grid when arc detected and fast turn-on the voltage for sustaining the beam current. Therefore the high voltage switch and arc current detection circuit are important part of the NBI power supply and there are much need for high voltage solid state switches in NBI system and a broad area of applications. This switch consisted of 100 series connected MOSFETs and adopted the proposed simple and reliable gate drive circuit without bias supply, Various results taken during the commissioning phase with a 100kW resistive load and NBI source are shown. This paper presents the detailed design of 120kV/70A high voltage MOSFETs switch and simple gate drive circuit. Problems with the high voltage switch and gate driver and solutions are also presented.

• 전기학회논문지
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• 제66권3호
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• pp.587-592
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• 2017

In the three-phase four-wire low-voltage power distribution equipment, single-phase and three-phase load have been used mainly mixed. Also linear and nonlinear loads have been used together in the same conditions. In a three-phase four-wire distribution line, the current distribution of three-phase linear load is almost constant in each phase during driving or stopping, but the single-phase load is different from each other for each phase in accordance with the operation and stop. So that the voltage unbalance is caused by the current difference of each phase. In the three-phase four-wire distribution system, non-linear load is used with linear load. The presence of single-phase nonlinear loads can produce an increase in harmonic currents in three-phase and neutral line. It can also cause voltage unbalance. In the present study, we analyzed for the voltage unbalance fluctuations by the operation pattern of the single and three-phase linear and non-linear load in three-phase four-wire low voltage distribution system.

• Journal of Advanced Marine Engineering and Technology
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• 제35권7호
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• pp.966-973
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• 2011

Power distribution onboard vessel is typically configured as ungrounded system due to the ability to continuously supply electric power even when an earth fault occurs. The impedance connections between 3 phase power lines and hull cause the line-to-hull voltages to become unstable and increased in case the impedances are unbalanced, bringing the situation susceptible to electric shock and deterioration of insulation material. Also the line-to-hull voltage can reach to a certain maximum value in the steady state depending on the distributed capacitances and grounding resistances between lines and hull. This study suggests how to find and calculate the maximum line-to-hull voltage in view of magnitude and phase angle based on the vector diagram.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 전력전자학술대회 논문집
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• pp.173-174
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• 2016

This paper proposes a comparison of Voltage Oriented Control (VOC) and Direct Power Control (DPC) under command mode transition for PMSG Wind Turbines (WT). Based on a neutral point clamped three level back to back type Voltage Source Converter (VSC), proposed control scheme automatically control the generated output power to satisfy a grid requirement from the hierarchical wind farm controller. Automatic command mode transition based on the dc-link voltage error provides a command mode changing between grid command and MPPT mode. It is confirmed through PLECS simulations in Matlab. Simulation result shows that proposed control scheme of VOC and DPC achieves a much shorter transient time of generated output power than the conventional control scheme of MPPT with optimal torque control and VOC under a step response. The proposed control scheme makes it possible to provide a good dynamic performance for PMSG wind turbines in order to generate a high quality output power.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.111-112
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• 2013

The three-phase four-leg voltage source inverter (VSI) topology can be an interesting option for the three phase-four wire system. With an additional leg, this topology can handle the neutral current, hence the DC link capacitance can be reduced significantly. In this paper the three dimensional space vector modulation (3D SVM) in ${\alpha}{\beta}{\gamma}$ coordinates for the three-phase four-leg VSI is presented. By using the 3D SVM method, the DC link voltage can be reduced by 16% compared with the split DC link capacitor topology and the output distortion can also be reduced under the unbalanced load condition.