• 조명전기설비학회논문지
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• 제27권4호
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• pp.8-15
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• 2013

This paper proposes a DC-link voltage variation compensation method for a 3-level single phase converter for high-speed trains. Since 3-level NPC(Neutral Point Clamped) type converters have the split DC-link causing the inherent problem of voltage fluctuations in the upper and lower capacitors, reducing the voltage difference between the top and bottom capacitors is required. In this paper, compensation time proportional to the voltage difference is added to PWM switching time to solve the voltage variation. The compensation time is obtained by a PI controller. Simulation results demonstrate the validity of the proposed method.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권4호
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• pp.457-463
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• 2012

Cascaded H-bridge multilevel inverters shows a useful circuit configuration to increase the number of output voltage levels to obtain high quality output voltage. By applying the concept of the power of three to dc voltage sources, it can increase the number of output voltage levels effectively. To realize this concept, two approaches may be considered. One is to use independent dc voltage sources pre-scaled in the power of three, and the other is to use instantaneous dc voltage sources generated from a cascaded transformer, which has the secondary turn-ratios scaled in the power of three in sequence. A common feature in both approaches is to use the concept of the power of three for dc voltage sources, and a point of difference is whether it adopts a low frequency transformer or not, and where the transformer is located. According to the difference, application areas are limited and show different characteristics on THD of output voltages. We compare and analyze both approaches for their circuit configurations, voltage level generating method, THD characteristics of output voltage, efficiency, application areas, limitations, and other characteristics by experiments using 500 [W] prototypes when they generate a 27-level output voltage.

• Restorative Dentistry and Endodontics
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• 제22권2호
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• pp.809-819
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• 1997

The purpose of this study was to develop an accurate frequency-dependent type apex locator. To compensate the impedence differences of different canal contents, voltage differences were pre-measured and stored for saline, HOsb1/$2O_2$ and NaOCl. The circuit was adjusted to recognize the different voltages of each solution, thereby the machine could automatically compensate the voltage differences. In the process of this study, the following informations were observed. 1. Most stable apical reading was obtained at 500Hz and 10kHz. 2. There were no differences in accuracy among three different frequency types, sign wave, triangular wave and rectangular wave(p>0.05). 3. Before the compensation of voltage differences, saline, H2O2 and NaOCl showed different readings at the apex even with the frequency-type (p<0.05). 4. After compensating the voltage difference, the accuracy was enhanced from + 0.42 to +0.32 in H2O2(p<0.05), from -0.34 to -0.12 in NaOCl(p<0.05).

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1997-2004
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• 2011

The $2{\times}25kv$ AT electric power feeding method in the A.C. electric train adopts the one-phase power feeding method as the standard due to a voltage phase difference, and the distance between the two neighboring substations is 50km due to voltage drop. The one-phase power feeding method makes the system operation feasible, while making it unfavorable for power supply. Moreover, railroad involves large-capacity single-phase load, and if it is expected to continue to rise, it is necessary to research on measures to stabilize the supply of power to railroad cars with the existing facilities. In this study, a parallel power feeding method between neighboring substations is proposed to stabilize the supply of electric power to electric railroad cars under the 2*25kv AT power feeding method and the loop current induced by voltage phase difference between the two neighboring substations during parallel power feeding is investigated.

• 한국초전도ㆍ저온공학회논문지
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• 제18권3호
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• pp.25-29
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• 2016

A quench detection system of KSTAR Poloidal Field (PF) coils is inevitable for stable operation because normal zone generates overheating during quench occurrence. Recently, new voltage quench detection method, combination of Central Difference Averaging (CDA) and Mutual Inductance Compensation (MIK) for compensating mutual inductive voltage more effectively than conventional voltage detection method, has been suggested and studied. For better performance of mutual induction cancellation by adjacent coils of CDA+MIK method for KSTAR coil system, balance coefficients of CDA must be estimated and adjusted preferentially. In this paper, the balance coefficients of CDA for KSTAR PF coils were numerically estimated. The estimated result was adopted and tested by using simulation. The CDA method adopting balance coefficients effectively eliminated mutual inductive voltage, and also it is expected to improve performance of CDA+MIK method for quench detection of KSTAR PF coils.

• Journal of the korean society of oceanography
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• 제37권3호
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• pp.160-168
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• 2002

We have been measuring the voltage differences by using submarine cables in the Tsushima and in the Tokara Straits. The aim of these measurements is to estimate the volume transports of the ocean currents through those straits. In this paper, the voltage differences are compared with the corresponding sea level and air pressure differences between straits. Especially in the Tsushima Strait, the voltage difference is consistent with the air pressure difference as well as the sea level difference.

• 한국정보통신학회논문지
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• 제15권4호
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• pp.891-896
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• 2011

이 논문에서는 전류 컨베이어 회로를 이용하여 입력 전압의 차에 비례하는 주파수 신호를 생성하는 회로를 설계하였다. 설계된 회로는 HSPICE를 이용하여 회로의 동작을 분석하였으며, 입력 전압 차는 수V에서 수mV 단위까지 변화시키면서 출력 주파수를 시뮬레이션하였다. 회로의 시뮬레이션 결과 이론적인 계산값과 비교하였을 때 에러는 -1.9%에서 +1.8% 이내였다.

• 전기학회논문지
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• 제65권1호
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• pp.9-15
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• 2016

Distribution networks are operated in radial fashion during the normal state. Loop configuration is also required temporally in case of live load transfer among the adjacent feeders. Voltage angles of each substation buses are very important data in order to calculate power flow of the loop structured distribution feeders. This paper proposes substation bus voltage angle calculation method using voltage angle difference measured at the normally open tie switches. Simulation case studies using Matlab simulink have been performed to establish feasibility of proposed method.

• 한국전기전자재료학회논문지
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• 제22권4호
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• pp.333-341
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• 2009

In this paper arc behavior in spiral type vacuum interrupter(VI) was analyzed by means of arc images, arc voltages and finite element method(FEM). As a result of experiment, the difference of arc voltage was observed under different twisting angles. It was found that the reason of the difference was the difference of arc resistance from simultaneous analysis of arc images and arc voltages. and the difference of arc resistance was explained by Lorentz force calculation with FEM. And the results of calculation were sufficient to explain the experimental results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.1018-1019
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• 2015

Recently, standby power reduction techniques of AC/DC adaptor were developed, consuming power almost arrived to 300mW level. The standby power losses are composed of the input filter loss 11.8mW, the control IC for AC/DC adaptor 18mW, the switching loss 9.53mW and the feedback loss 123mW. And there are the standby power reduction techniques. In this paper, in order to reduce the standby power of SMPS more, the loss due to a voltage difference between input and output is reduced by the control circuit which is composed of the low voltage driving circuit and voltage regulator. The low voltage driving circuit operates on the low voltage of input and off the high voltage. The low voltage driving IC was produced by the $1.0{\mu}m$, high voltage DMOS process.