• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제54권9호
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• pp.403-407
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• 2005

Most of the loads in industrial power distribution systems are balanced and connected to three power systems. However, voltage unbalance is generated at the user's 3-phase 4-wire distribution systems with single & three phase. Voltage unbalance is mainly affected by load system rather than power system. Unbalanced voltage will draws a highly unbalanced current and results in the temperature rise and the low output characteristics at the machine. It is necessary to analyse correct voltage unbalance factor for reduction of side effects in the industrial sites. Voltage unbalance is usually defined by the maximum percent deviation of voltages from their average value, by the method of symmetric components or by the expression in a more user-friendly form which requires only the three line voltage readings. If the neutral point is moved by the unbalanced load at the 3-phase 4-wire system. Line and phase voltage unbalance leads to different results due to zero-sequence component. So that it is difficult to analyse voltage unbalance factor by the conventional analytical method, This paper presents a new analytical method for phase and line voltage unbalance factor in 4-wire systems. Two methods indicate exact results.

• 조명전기설비학회논문지
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• 제16권1호
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• pp.76-84
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• 2002

송전선과 배전선의 고장에 의한 voltage sag는 산업 수용가와 전력회사에 당면한 가장 중요한 전력품질(power quality) 문제들 중 하나가 되었다. voltage sag는 일반적으로 진폭과 지속시간 특성으로 기술되지만 voltage sag 현상을 규명하여 그 대책을 찾는데는 위상변위 특성을 반드시 고려해야 한다. 이 논문에서는 3상지락, 단선지락, 및 선간단락 사고가 발생하였을 경우에, 고장임피던스의 변화에 의한 voltage sag를 symmetrical components 해석을 이용하여 특성해석을 하였다. 이 때, voltage sag와 이들이 진폭과 위상에 미치는 효과를 고찰하였다. 3상지락과 같은 평형 고장은 모든 상에서 전압과 전류가 동일한 값으로 변화되고 또한 영상성분들은 영이 되었다. 그렇지만, 단선지락과 선간단락 고장과 같은 불평형 고장으로 인한 voltage sag는 진폭과 위상이 각 상마다 다르게 변화되었다. 해석결과를 확인하기 위하여 전력회로 모델들을 토대로 시뮬레이션을 수행하고 그 결과들도 검토되었다.

• 전기학회논문지P
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• 제53권2호
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• pp.58-64
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• 2004

Most of the loads in industrial power distribution systems are balanced and connected to three power systems. However, in the user power distribution systems, most of the loads are single & three phase and unbalanced, generating voltage unbalance. Voltage unbalance is a condition in a polyphase system in which the rms values of the line-to-line voltages or the phase angles between consecutive line-to-line voltages, are not all equal. Slight voltage unbalance generates a disproportionately high current unbalance at the motor stator winding. This paper presents a scheme on operation states of a three-phase induction motor under unbalanced voltages. The three-phase voltages applied to the stator winding of the studied induction motor are controlled by respectively adjusting the magnitude and phase angle of each phase. The voltage unbalanced factor(VUF) of the three-phase source voltages can then be varied to examine the different values of VUF on machine's operation characteristics.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 추계학술대회 논문집
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• pp.87-88
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• 2014

The paper presents a novel phase locked loop(PLL) control method for robust three-phase thyristor dual converters under sag, notch, and phase loss conditions. This method is applied to three line to line voltages of grid to derive three phase angle errors from three separated single-phase PLLs. They can substitute for abnormal phase to guarantee the synchronization in the various grid fault conditions. The performance of novel PLL with moving average method is verified through simulations.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권3호
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• pp.384-390
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• 2012

This paper proposes a fault diagnosis method of the line-to-line voltage sensors in 3-phase AC/DC pulse width modulation (PWM) converters. The line-to-line voltage sensors are an essential device to obtain the information of the grid voltages for controlling the 3-phase AC/DC PWM converters. If the line-to-line voltage sensors are mismeasured by various faults, the voltage sensors can obtain wrong information of the grid voltage. It has an adverse effect on the control of the converter. Therefore, the converter causes the unbalance input AC current and the DC-link voltage ripple in the 3-phase AC/DC PWM converter. Hence, fast fault detection and fault tolerant control are needed. In this paper, the fault diagnosis method is proposed and verified through simulations and experiments.

• 한국산학기술학회논문지
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• 제7권6호
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• pp.1072-1077
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• 2006

본 논문은 AC 라인 리액터와 2개의 4레그 PWM 전압형 컨버터를 사용하여 병렬 및 직렬 능동필터 기능을 가지는 새로운 3상 Line-Interactive UPS 시스템을 제안하고 전압제어 방식을 설명한다. 제안하는 UPS 시스템의 병렬 및 직렬 PWM 전압형 컨버터에서 전압제어의 목적은 정상상태 및 과도상태에서 만족스러운 동작 특성을 보장하는 것이다.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 춘계학술대회논문집
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• pp.74-77
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• 2005

Most of the loads in industrial power distribution systems are balanced and connected to three power systems. However, voltage unbalance is generated at the user's 3-phase 4-wire distribution systems with single & three phase. Voltage unbalance is mainly affected by load system rather than power system. Unbalanced voltage will draws a highly unbalanced current and results in the temperature rise and the low output characteristics at the machine. It is necessary to analyse correct voltage unbalance factor for reduction of side effects in the industrial sites. Voltage unbalance is usually defined by the maximum percent deviation of voltages from their average value, by the method of symmetrical components or by the expression in a more user-friendly form which requires only the three line voltage readings. If the neutral point is moved at the 3-phase 4-wire system by the unbalanced load, by the conventional analytical method, line and phase voltage unbalance leads to different results due to zero-sequence component. This paper presents a new analytical method for phase and line voltage unbalance factor in 4-wire systems. Two methods indicate exact results.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2004년도 춘계학술대회
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• pp.193-197
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• 2004

The four-leg Voltage Source Converter(VSC) can use the DC link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by $15\%$ in comparison to that of the conventional line-interactive UPS system. In this paper a novel line interactive Uninterruptible Power Supply(UPS) using the two four-leg VSCs is proposed. One VSC is in parallel with the ac link reactor of the power source side, and the other is in series with the load. The parallel four-leg voltage source inverter controls the three-phase line voltage independently in order to control the line reactor current indirectly. It eliminates the neutral line current and the active ripple power of the source side using the pqr theory so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series four-leg voltage source inverter compensates the line voltage and allows it to be balanced and harmonic-free. Both of the parallel and series four-leg voltage source inverters always act as independently controllable voltage sources, so that the three-phase output voltage shows a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through computer simulations results.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.201-203
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• 2005

A new 3-phase line-interactive UPS(Uninterruptible Power Supply) system with parallel-series active power-line conditioning capability using AC line reactor and two four-leg PWM VSCs(Voltage Source Converters) was introduced recently, In this paper, the strategy of voltage control in suggested UPS system is explained. The objective of proposed voltage controllers in parallel(shunt) and series PWM VSC is to guarantee satisfactory characteristics in steady state and transient state.

• 대한전기학회논문지:전력기술부문A
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• 제51권9호
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• pp.460-466
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• 2002

A reliable fault phase selection algorithm plays a very important role in transmission line protection, Particularly in Extra High Voltage (EHV) networks. The conventional fault phase selection algorithm used the phase difference between positive and negative sequence current excluding load current. But, it is difficult to pick out only fault current since we can not know when a fault occurs and select the fault phase in weak-infeed conditions that dominate zero-sequence current in phase current. The proposed algorithm can select the accurately fault phase using the sum of unit vectors which are calculated by positive-sequence voltage and negative-sequence voltage.