• KIEE International Transactions on Power Engineering
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• 제5A권3호
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• pp.252-259
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• 2005

Various problems such as increase of power loss and voltage instability may often occur in the case of low load power factor. The demand of reactive power increases continuously with the growth of active power and restructuring of electric power companies makes the comprehensive management of reactive power a troublesome problem, so that the systematic control of load power factor is required. In this paper, the load power factor sensitivity of generation cost is derived and it is used for effectively determining the locations of reactive power compensation devices and for enhancing the load power factor appropriately. In addition, voltage variation penalty cost is introduced and integrated costs including voltage variation penalty cost are used for determining the value of load power factor from the point of view of economic investment and voltage regulation. It is shown through application to a large-scale power system that the load power factor can be enhanced effectively using the load power factor sensitivity and the integrated cost.

• 대한전기학회논문지:전력기술부문A
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• 제55권12호
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• pp.514-521
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• 2006

The existing ULTC operation control strategy based on the measured data deteriorates the voltage compensation capability making the efficient corresponding to the load variation difficult by following the fixed load center point voltage. Accordingly, this paper proposes a new on-line fuzzy ULTC controller based on the designed multiple load center points which can improve the voltage compensation capability of ULTC and minimize voltage deviation by moving in real-time the load center point according to the load variation to an adequate position among the multiple load center points designed using the clustering technique. The Max-Min distance technique is adopted as the clustering technique for the decision of multiple load points from measured MTr load current and PTr voltage, and the minimum distance classifier is adopted for the decision of fuzzy output membership function. To verify the effectiveness of the proposed strategy, Visual C++ MFC-based simulation environments is developed. Finally, the superiority the proposed strategy is proved by comparing the fuzzy ULTC operation control results based on multiple load center points with the existing ULTC operation control results based on fixed load center point using the data for three day.

• 전기학회논문지
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• 제66권3호
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• pp.587-592
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• 2017

In the three-phase four-wire low-voltage power distribution equipment, single-phase and three-phase load have been used mainly mixed. Also linear and nonlinear loads have been used together in the same conditions. In a three-phase four-wire distribution line, the current distribution of three-phase linear load is almost constant in each phase during driving or stopping, but the single-phase load is different from each other for each phase in accordance with the operation and stop. So that the voltage unbalance is caused by the current difference of each phase. In the three-phase four-wire distribution system, non-linear load is used with linear load. The presence of single-phase nonlinear loads can produce an increase in harmonic currents in three-phase and neutral line. It can also cause voltage unbalance. In the present study, we analyzed for the voltage unbalance fluctuations by the operation pattern of the single and three-phase linear and non-linear load in three-phase four-wire low voltage distribution system.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.940-947
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• 2011

Load capacity varies according to a day of the week in traction power supply system, because time schedule in railway is changed as demand for passengers and freights. Therefore, Voltage drop also varies as load capacity. In Korea railway, Voltage collected from catenary in train is decreased, as load supplied traction power supply system is increased. Therefore, investigation about voltage drop should be performed, before development of countermeasure against voltage drop. The investigation can be performed by simulation or field test. Naturally, field test is more precise than simulation. In addition, field test should be carried out at peak load. This paper presents test and analysis about voltage drop in railway. The test is performed in both a day of the week and weekend. The analysis is figured out comparison load capacity between two days and voltage drop across terminal.

• 조명전기설비학회논문지
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• 제27권2호
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• pp.45-53
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• 2013

In this paper, we analyze the typical phase voltage and line current waveform characteristics of the distribution system with 3 phase small synchronous generation source in case with load and non-load group, in order to investigate the power quality for end load connected of generation source. As demonstrated by our experimental results, the distortion and power quality of phase voltage and line current waveform were relatively good for low voltage 3 phase model grids connected of 3 phase small synchronous generation source in case with non-load group. However, distortion and power quality of voltage and current waveform was poor for low voltage 3 phase model grids connected to 3 phase small synchronous generation source in the load group with some phase voltage and frequency difference. From the above results, we conclude that the phase voltage and frequency of 3 phase generation source must be identical to that of distribution system source to maximize the power quality. Also, special attention is required in case of having load group or non-load group to 3 phase generation source.

• 전기학회논문지
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• 제65권4호
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• pp.567-575
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• 2016

This paper proposed the voltage control of stand-alone inverter for power quality improvement under unbalanced and non-linear load. The 3-phase DC-AC inverter controls CVCF(Constant Voltage Constant Frequency) and selective harmonic eliminate method in stand-alone mode by PR controller, and the stand-lone inverter supplies stable sinusoidal voltage to balanced, unbalanced and non-linear loads. The total harmonic distortion(THD) of line-to-line load voltage($V_{LL}$) is 1.2% in the balanced load. THD of $V_{LL}$ is reduced from 5.2% to 1.4% and 6.7% to 3.5%, respectively unbalanced and non-linear load. The stand-alone inverter can be supplies sinusoidal balanced voltage to unbalanced load because the voltage unbalanced factor(VUF) of $V_{LL}$ is reduced from 5.2% to 1.4% in the unbalanced load. Feasibility of control method for a stand-alone inverter will be verified through 30kW stand-alone inverter system.

• 전기학회논문지P
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• 제59권2호
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• pp.141-145
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• 2010

Most of the industrial loads includes the non-linear load as well as the linear load because there are many kinds of power conversion equipments at the input stage of the load in distribution network. The non-linear load causes the distortion of voltage waveform at PCC because the non-linear load generates the harmonic current. As a result, various voltage harmonics are existed at PCC depending on the current harmonics from the non-linear load. And, a series reactor is generally connected to the power capacitor in series to attenuate the distortion of voltage waveform and to reduce an inrush current of power capacitor. Also, harmonic current of power capacitor is highly dependent on the series reactor because it is operated with the power capacitor as a passive filter against nonlinear loads. Then, these capacitors might be damaged by the excessive voltage and current harmonic components. In this paper, we presented how to select the capacitor and series reactor to meet the requirement of the voltage distortion at PCC and analyzed the voltage, current and capacity rating of the power capacitor by the computer simulation to ensure the safe operation of power capacitor when the voltage harmonics at PCC are existed. Also, the analysis data were compared with the experimental measurements for the verification.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
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• pp.110-112
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• 1995

Now days, voltage stability is well recognized as an important problem. It is well known that voltage stability is influenced by the characteristics of load. Up to present, voltage stability researches were done by the static load modeling, but it is needed that the precise analysis by the view point of dynamic load modeling. In this paper, with induction motor as dynamic load, I show the voltage collapse mechanism followed by load increase. Then I propose the protective method of voltage collapse by using TCSC.

• 전기학회논문지
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• 제59권6호
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• pp.1034-1040
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• 2010

This paper presents a calculation method of the area of severity for the stochastic assessment of voltage sags. In general, the annual expected numbers of voltage sags at an individual load point can be estimated stochastically. However, in order to assess the system voltage sag performance considering many sensitive load points together, it is necessary to determine and analysis the area of severity for the load points. The area of severity to voltage sags is the network region where the fault occurrences will simultaneously lead to voltage sags at different load points. In this paper, the concept of the voltage sag assessment and the calculation method of the area of severity are addressed. The analysis of the area of severity is performed on the IEEE 30-bus test system by using the proposed method. The method is useful for the stochastic assesment of voltage sags and the establishment of systematic plans for voltage sag mitigation.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1996년도 창립기념 전력전자학술발표회 논문집
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• pp.71-75
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• 1996

As the Three-level ZVS PWM DC-DC converter operates likewise full-bridge ZVS PWM DC-DC converter and the blocking voltage of each switching device is a half of the DC-link voltage, it is suitable for the high imput voltage applications. However, it has some problems as follows; The blocking voltage of each devices is unbalanced and it causes the power losses of the inner switching devices to be increased. Also, it has narrow load range so that the switching losses and the efficiency are reduced as it goes to the light load. This paper presents an nove Three-level ZVS PWM DC-DC converter, which can reduce the overvoltage of the outer switches, eliminate the unbalance of the voltage sharing between the switches at turn-off due to the stray inductances, and operate from no load to full load. The characteristics and the performances of the proposed Three-level ZVS PWM DC-DC converter are verified by simulation and experimental results