• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.525-526
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• 2006

Recently, much research has been done and many improvements have been developed for islanding protection of distributed generation(DG). Anti-islanding protection for DG must be act very quickly to prevent equipment damage at the time of disconnection and for the safety of maintenance and repair personnel. DG-based detection methods have included both passive and active types, and now research has shifted towards new anti-islanding detection methods that make up for the defects of the previous types. Because differences occur between the utility grid and the DG when connecting and disconnecting depending on the phase difference, voltage, current, relative capacity of electric power, and system operation characteristics, voltage phase angle is an important consideration. In this paper, we simulated islanded operation characteristics comparing phase difference of DG and the connected utility grid, and analyzed various parameters (real power, reactive power, RMS voltage, RMS current, power factor angle, and frequency) by varying the DG's voltage phase angle. Using this information, we propose a suitable DG voltage phase angle for enhanced passive islanding detection techniques.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.7
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• pp.440-444
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• 2016

Titanium oxide ($TiO_2$) thin films were synthesized on polymer insulator and Si substrates by atomic layer deposition (ALD) method. The surface and electrical properties of $TiO_2$ films synthesized at various ALD cycle numbers were investigated. The synthesized $TiO_2$ films exhibited higher contact angle and smooth surface. The contact angle of $TiO_2$ films was increased with the increase of ALD-cycle number. Also, the rms surface roughness of films was slightly rough with the increase of ALD-cycle number. The leakage current on $TiO_2$ film surface synthesized at various conditions were uniformed, and the values were decreased with the increase of ALD-cycle number. In the results, the performance of $TiO_2$ films for self-cleaning critically depended on a number of ALD-cycle.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1422-1423
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• 2006

In our study, the PTFE nozzle ablation in the high-voltage self-blast type $SF_6$ gas circuit breaker was investigated. The test circuit breaker has the structure that the pin electrode is moving and the pressure reservoir volume and the dimension is almost same as commercial 145kv 40kA circuit breaker for similar result in real circuit breaker. The variation of current and arcing time was the range of $36kA_{rms}$(symmetry) - $40kA_{rms}$(asymmetry) and 10-16 ms. From the measured data the tendecy of the mass loss of the nozzle to current load and arc energy was estimated. In this process, the distance from the arc to nozzle(PTFE) surface, area which was exposed to arc and stroke contour was considered. These results will be used to enhance the accuracy of the computational fluid dynamics analysis in circuit breaker and estimate the residual life time of a circuit breaker.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.2
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• pp.150-158
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• 2017

This study proposes a new pulse-width modulation switching pattern for the low conduction loss of a three-level neutral point clamped (NPC)-based dual-active bridge (DAB) converter. The operational principle for a bidirectional power conversion is a phase-shift modulation. The conventional switching method of the three-level NPC-based DAB converter shows a symmetric switching pattern. This method has a disadvantage of high root-mean-square (RMS) value of the coupling inductor current, which leads to high conduction loss. The proposed switching method shows an asymmetrical pattern, which can reduce the RMS value of the inductor current with lower conduction loss than that of the conventional method. The performance of the proposed asymmetrical switching method is theoretically analyzed and practically verified using simulation and experiment.

• Journal of Power Electronics
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• v.18 no.1
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• pp.45-55
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• 2018

It is usually difficult for dual-active-bridge (DAB) dc-dc converters to operate efficiently at light loads. This paper presents an in-depth analysis of a DAB with triple-phase-shift (TPS) control under the light load condition to overcome this problem. A kind of operating mode which is suitable for light load operation is analyzed in this paper. First, an analysis of the zero-voltage-switching (ZVS) constraints for the DAB converter has been carried out and a reasonable dead-band setting method has been proposed. Secondly, the basic operating characteristics of the converter are analyzed. Third, under the condition of satisfying the ZVS constraints, both the reactive power and the root mean square (RMS) value of the current are simultaneously minimized and a particle swarm optimization (PSO) algorithm is employed to analyze and solve this optimization problem. Lastly, both simulations and experiments are carried out to verify the effectiveness of the proposed method. The experimental results show that the converter can effectively achieve ZVS and improved efficiency.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.686_687
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• 2009

The traceability maintenance system for the AC voltage and current has been developed at the frequency range of 20 Hz to 100 Hz without using any compensation technique which is used at thermal converter (TC) ac-dc transfer system at low frequencies. The system uses a digital voltmeter (DVM) as a data acquisition system of the input waveform and stored data in memory. The developed algorithm acquires and processes the sampling data to calculate the root mean square (rms) value of the input voltage of DVM which operates at DC 10 V range for better accuracy. The best uncertainty of the AC voltage measurements is $3 {\mu}V/V$ within the frequency range. The best uncertainty of the AC current measurements is better than the $5 {\mu}A/A$ and mainly depend on the current to voltage converter, ac-dc current shunt or Current Transformer (CT), used for the measurement

• Progress in Superconductivity and Cryogenics
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• v.12 no.3
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• pp.39-43
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• 2010

In Korea, 22.9kV hybrid SFCL (Superconducting Fault Current Limiter) has been developed and carried out long-term field tests in Gochagn power test center of KEPCO through DAPAS program. The SFCL will be installed at a distribution line of Icheon substation in Korea. For the successful application, we have to design the specifications considering real power system operation. This paper proposes a concept of the operating current based rms value for the protection coordination with protective delays and studies a proper range of the current in Korean distribution power system.

• Journal of Power Electronics
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• v.14 no.5
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• pp.874-881
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• 2014

This study presents a single-phase power factor correction AC-DC converter that operates in discontinuous conduction mode. This converter uses the pulse-width modulation technique to achieve almost unity power factor and low total harmonic distortion of input current for universal input voltage $90V_{rms}$ to $264V_{rms}$) applications. The converter has a simple structure and electrical isolation. The magnetizing-inductor energy of the transformer can be recycled to the output without an additional third winding. The steady-state analysis of voltage gain and boundary operating conditions are discussed in detail. Finally, experimental results are shown to verify the performance of the proposed converter.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.265-267
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• 2003

The wavelet transform(WT) has been extensively applied in solving many problems in applied science and engineering following its introduction in early 1980's. The WT analyzes a signal in a changeable frequency range by employing a moving window whereby along time window is used to obtain low frequency information and short time window is used to obtain high frequency information. In this paper, after various fault types in 154 KV transmission system was simulated by using EMTP, and the RMS values by changing Mother wavelet was calculated by applying wavelet transform to the simulated voltage and current signal.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.240-241
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• 2017

멀티레벨 방식의 Dual Active Bridge 컨버터는 기존의 컨버터와 비교하여 높은 자유도의 스위칭 방식을 가진다. 본 논문에서는 멀티 레벨 방식의 DAB 컨버터의 동작원리를 분석하고, 인덕터 전류의 RMS 값과 THD를 최소화하기 위하여 기본파를 제외한 3 고조파와 5 고조파를 감쇄하는 스위칭 방식을 제안한다. 다양한 스위칭 패턴에 따른 인덕터 전류 RMS 값과 THD를 비교하여 제안하는 스위칭 방식의 타당성을 검증하고자 한다.