• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1339-1340
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• 2013

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.323-326
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• 2003

본 논문에서는 THD 개선을 위한 단순한 구조의 단일 단 PFC를 제안하고 벅 컨버터에 적용하였다. 제안한 회로는 밸리-필 정류회로와 부스팅을 위한 인덕터를 결합하여 단일 능동 소자로 DC/DC 변환 과 PFC를 동시에 수행한다. 제안된 회로에서의 입력전류 모양은 입력전압조건과 PWM 스위칭 시간에 관계되고, 부스팅 인덕터에 의해 능동스위치 차단시간동안 입력 전류를 제어하여 THD를 개선한다. 부스팅 인덕터 채용에 따른 동작해석과 최적 THD를 위한 인덕터를 선정하고 100W출력 단일 단 컨버터를 설계, 제작하였다. 실험에 의한 측정된 결과로 제안된 컨버터의 타당성을 검증하였다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.3
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• pp.361-366
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• 2012

This paper analyzes the THD(Total Harmonics Distortion) according to output power fluctuation of photovoltaic(PV) systems using real time simulator. For being close to reality, the PV system including inverter and MPPT(Maximum Power Point Tracking) which composed of closed-loop using real-time simulator are modeled. The change of irradiance and temperature of PV module is modeled to consider the change of weather. The various simulations according to the weather conditions are performed and THD is calculated at each condition. In this paper, the results by off-line simulation are compared with the ones of real time simulation.

• Proceedings of the KIPE Conference
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• 2010.11a
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• pp.17-19
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• 2010

In this paper, new PWM method is proposed to reduce input current THD of PWM Rectifier. In general, the carrier comparison PWM method is used for PWM rectifier in which triangle wave is used as a carrier wave. However, large d-axis current ripple by this method can be a source of large THD. In this paper, new carrier comparison PWM method is proposed in which sawtooth wave is used as a carrier wave. Depending on the phase of the voltage commands, the rising or falling sawtooth wave is selected to reduce the THD. The simulation results verified the performance of the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.28 no.1
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• pp.1-7
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• 2023

A grid-connected 3-level NPC inverter is a power conversion device that connects renewable energy generators, such as photovoltaic or wind turbines to the grid. Although many studies have focused on this inverter, commercializing it requires strictly satisfying various safety and power quality-related standards. Among many standards, leakage current and grid current total harmonic distortion(THD) can be affected by external factors such as installation environment, aging, and grid conditions. Hence, inverter operations that can satisfy these standards need to be explored. In this study a 3-level NPC inverter operation algorithm using the Phase Opposition Disposition-PWM method that can effectively reduce leakage current and switching frequency adjustment to reduce THD effectively has been proposed.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.97-98
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• 2011

The HVAC(Heating Ventilation and Air conditioning) system is controlled by two ways, one is ON/OFF control and the other is PWM inverter with V/F. Control of blower with the use of PWM inverter has quite some benefits such as the capability of changing speed, high efficiency and reduced noise level compared with ON/OFF control. But if blower is operated at low speed, high THD generated by decrease of ma, and output voltage lowered in proportion to frequency. To solve these problems, filter should be installed at the output stage of inverter, which can decrease THD but has problems such as increase of volume size and additional braking resistance. This paper proposes the PWAM method which can reduce THD instead of installing the filter at the output stage of inverter. The proposed PWAM method is an inverter modulation method that fixes the modulation index of inverter to reduce THD by varying DC link voltage of inverter unlike conventional PWM method. Finally, the validity of proposed PWAM methods verified by experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.6
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• pp.526-534
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• 2022

The modular multilevel converter (MMC) has been widely applied to various industrial areas because of its various advantages and structural characteristics. Therefore, many methods for synthesizing the output voltage of MMC have been studied. Among these methods, phase-shifted pulse width modulation (PSPWM) is frequently used in MMC systems because it has diverse merits, such as excellent output qualities even with a small number of cells and uniform power distribution among cells. In this study, the total harmonic distortion (THD) of the output voltage is analyzed in accordance with the number of cells in one arm of a single-delta bridge cell MMC in order to compare PSPWM methods in terms of the THD of the output voltage. The physical characteristics of the triangle and sawtooth carrier waves used for the PSPWM and the mathematical modeling of output voltage are introduced. Then, the obtained results are verified through real-time simulation of a 1 MW single-delta bridge cell MMC system.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1994.06a
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• pp.21-27
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• 1994

본 연구에서는 대형 틸팅패드 저어널베어링의 성능에 관한 보다 정확한 설계 자료를 제시하기 위해서 선단압력을 고려한 이론해석을 수행하여 선단압력이동 베어링의 THD 성능에 미치는 영향을 제시하고자 한다. 그리고, 이론해석 결과와 실험 결과를 비교하여 이론해석 결과의 타당성을 제시하고자 한다.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.201-202
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• 2011

This paper compares the effect on transient stability by according to application of adaptive autoreclouse using THD with the one of conventional autoreclosure. These two autoreclousure methods are modeled by EMTP/MODELS and simulated according to various fault locations and fault clearing times. This paper analyzes transient stability using simulation results.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1236-1237
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• 2011

본 논문에서는 두 대의 5-레벨 인버터를 직렬 결합하여 출력 전압에 25 레벨을 형성할 수 있는 멀티레벨 인버터의 입력전압원으로 사용되는 직렬 결합된 커패시터 전압의 불평형에 따른 출력전압의 THD 변화를 분석한다. 25-레벨 인버터의 구동을 위해 등면적법에 의해 계산된 스위칭 각을 적용하고, 상단, 하단 모듈 입력전압 크기의 1, 5, 10, 15, 20 %의 변동에 대해 시뮬레이션을 수행하고 결과를 분석한다.