• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.131-133
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• 1995

Inductive high-Tc superconducting fault current limiter using YBCO superconducting ring in the secondary part has many advantages in power networks. It is based on the superconducting to normal transition and this paper describes its operational characteristics and experimental results, especially focused on the harmonic component analysis and recovery time. We fabricated and tested it under various conditions for the analysis of transient fault characteristics. And for the analysis of harmonics we used FFT methods. The superconducting ring was quenched in 240Arms and fault current was effectively limited to the lower current level. In addition, it was fast recovered when the fault condition was removed and after fault the system had odd harmonics.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전력기술부문
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• pp.119-121
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• 2004

This paper presents a methodology which can make alternatives of distribution system, and can calculate reliability costs, harmonics costs, and construction costs. And by using total cost of the system, decision maker can select the most economic and reasonable alternative. As a result, not only we can decide most economical and reasonable result, but we can get proper reliability and harmonics level. The usefulness of the method is verified by applying it to the test system.

• 반도체디스플레이기술학회지
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• 제13권4호
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• pp.43-48
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• 2014

Two-level inverter has some disadvantages like high harmonics contained in the output current, efficiency limit and stress to switching device as IGBT and FET. Many researches have reported multi-level inverter to complement two-level inverter of problems. In this paper, we suggest MPPT algorithm of multi-string three-level solar inverter that considered nowadays. We added midpoint controller in order to implement the MPPT algorithm because the three-level inverter has to need midpoint controller and procured the stability of direct current link. We verify the superiority of multi-string T-Type inverter and the algorithm we suggested with solar irradiance variation experiment and MPPT efficiency measurement. The MPPT efficiency was confirmed with a high efficiency more than 99.97%.

• 한국철도학회논문집
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• 제9권6호
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• pp.761-765
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• 2006

At present, harmonic currents cause serious problems in power conversion system using the semiconductor switching device. Also some of the conversion system provokes harmonic currents against to the main power supply system and causes hindrances for the system. Main power impedance of the traditional LC passive filter method, influences on the filter characteristics and amplifies the harmonics when resonance phenomenon is occurred. And the traditional existing 2 level inverter systems show the limit in capacity of voltage and current in case of occurring sudden load change. So, to solve this problem active filter which uses cascaded H-bridge multi level inverter has been designed and ex-filter system circuits were totally investigated. With multi level active filtering system not only the size of filter but also the size of filter for transformer can be reduced by half and so as to the weight, while the capacity of inverter can be double sized and wave forms can be compensated exactly and precisely. Also by the benefit of the increase in rating capacity, the various currents owing to the load fluctuation can be dealt more steadily. In order to simulate the wave form of harmonics based on the measured data on the AC 25kV high speed Domestic Commercial railway, it was simulated with PSCAD/EMTDC and PSIM. Based on the results of this demonstration, the power supply system and inverter system would be more stable and also promoting its efficiency.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.339-341
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• 1996

The objective of this paper is to present the design of a Neural Network(NH) based optimal pulse-width modulation(PWM) techniques for a three-level power inverter. Considering the importance of safety, power factor and harmonics of power inverters, two-level type and three-level type of power inverters using NNs are precisely investigated and compared in computer simulation.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1997년도 전력전자학술대회 논문집
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• pp.352-356
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• 1997

This paper present the design of a novel neural-network (NN) based pulse-width modulation (PWM) techniques for a three-level power converter of electric trains along with nonlinear mapping of essential switching patterns and fault tolerance, which are inherent characteristics of NNs. Considering the importance of safety, power factor and harmonics of electric train power converters, two-level type and three-level type of power converters using NNs are precisely investigated and compared in computer simulation. A computer simulation shows that a new current control scheme provides an improved performance over a fixed-band hysteresis current control in many aspects.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.491-494
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• 1994

The 3-level inverter is applied to the induction motor drive as the voltage type inverter for large poller one. This inverter divides the DC link voltage into the two parts and it is supplied to the inverter. The 3-level inverter can reduces the voltage between the each devices, and get more sinusoidal current waveform. This paper presents the new PWM method which can reduces the harmonics. The modulation at the inverter side is implemented using a DSP microprocessor.

• Journal of Power Electronics
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• 제16권2호
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• pp.522-531
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• 2016

This paper proposes a new NLC (Nearest Level Control) scheme for MMCs (Modular Multilevel Converters), which offers voltage ripple reductions in the DC capacitor of the SM (Sub-Module), the output voltage harmonics, and the switching losses. The feasibility of the proposed NLC was verified through computer simulations. Based on these simulation results, a hardware prototype of a 10kVA, DC-1000V MMC was manufactured in the lab. Experiments were conducted to verify the feasibility of the proposed NLC in an actual hardware environment. The experimental results were consistent with the results obtained from the computer simulations.

• Journal of Power Electronics
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• 제18권6호
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• pp.1650-1658
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• 2018

Multilevel converters are being widely used in medium-voltage high-power applications including motor drive systems, utility power transmission, and distribution systems. Selective harmonic elimination (SHE) is a well-known modulation method to generate high quality output voltage waveforms. This paper presents a new simple practical method for generating a generalized five-level waveform without selected low order harmonics. This method is based on a phase-shifted expression for the SHE problem, which can analytically calculate the exact values of switching angles and the feasible modulation index range for three-level and five-level waveforms. The proposed method automatically determines the number of transitions between levels and generates proper output waveform without solving complex trigonometric equations. Due to the simplicity of the computational burden, the real-time implementation of the proposed algorithm can be performed by a simple processor. Simulation and experiment results verify the correctness and effectiveness of the proposed method.

• 한국화재소방학회논문지
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• 제29권6호
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• pp.91-97
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• 2015

초고층건축물이나 대형 사업장과 IT를 추구하는 수용가는 많은 가전기기 사용하여 선형, 비선형부하시의 고조파로인한 Capacitor의 과열 및 소손, 자료 손상, 대지전위 상승, 통신유도장해등을 일으켜 전력설비의 오동작과 과열로 화재의 원인이 될 수 있다. 이를 확인하기 위해 건축물의 7곳을 조사하여 비교한 결과 6곳에서는 적정하였으나 1곳은 고조파관리가 필요하였다. 전류 고조파는 No. 3, 6, 7은 매우 초과하여 정밀 진단이 필요하였으며 No. 2, 3, 5는 5고조파 전류를 고려하여야 한다. R상 전압고조파는 양호하였으나 전류고조파는 No. 1을 제외하고 No. 2, 3, 4, 5, 6, 7은 모두 기준을 초과하였다. 따라서 지그재그변압기나 엑티브필터를 설치하여 고조파 상승을 억제시킬 필요가 있고 설비불평형률, 역률등을 종합 조사하여 효율도 향상시킬 필요가 있다.