• 대한전기학회논문지:전력기술부문A
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• 제49권2호
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• pp.56-61
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• 2000

In the paper, the system loss sensitivity index that implies the incremental system loss with respect to the change of bus power is derived using optimization technique. The index λ reaches $\infty$ at critical loading point and can be applied to actual power systems for following purposes. 1) Evaluation of system voltage stability 2)Optimal investment of reactive power focused on minimizing system loss and maximizing system voltage stability 3)Optimal re-location of reactive power focused on minimizing system loss and maximizing system voltage stability 4)Optimal load shedding in case of severe system contingency focused on minimizing system loss and maximizing system voltage stability. Case studies for each application have proved their effectiveness.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 A
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• pp.302-304
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• 1999

Voltage sag and swell are the most severe factors affecting power quality in distribution systems. This paper discusses an approach to ensure a high quality power supply to critical loads appling voltage-sag compensator. The proposed system consists of a PWM voltage source inverter, connected in series with the line through a single-phase transformer. The operation Principle and Power circuit configuration of the proposed voltage sag compensator are introduced. And then the transfer function of compensator is derived from simplified single phase power circuit, and simulated so that the benefits of this proposed compensator is confirmed through the open loop response.

• 전기의세계
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• 제31권3호
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• pp.197-203
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• 1982

The effects on the characteristics of 20-W fluorescent lamp were studied when applying magnetic field to its positive column. First, when the direction of the magnetic field is axial, i.e., along the lamp, if the magnitude of the field is stronger than the critical field, lamp voltage is increased, lamp current decreased, luminous flux increased, starting voltage decreased, as increasing the applied magnetic field. At the magnetic flux density is 130 gauss, luminous flux is increased to about 6 percents and starting voltage is increased to about 45 percents. Second, when the direction of the magnetic field is transverse to the lamp axis, as increasing the applied magnetic field, lamp voltage is increased, lamp current decreased, luminous flux increased and starting voltage is nearly constant, but the rates of increase or decrease of this case is different from those of the first. At the magnetic flux density is 300 gauss, luminous flux is increased about 45 percents. In both cases, electric power dissipated by lamps is the same as that of the lamp which magnetic field is not applied to.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.487-490
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• 2001

Power Quality and Reliability are becoming important issues for critical and sensitive loads. This paper describes the Line Interactive UPS with the function of Voltage Compensator that is 'Line interactive Dynamic Voltage Restorer(LIDVR). The main purpose of a LIDVR is to compensate for voltage sag(dip), outage and overvoltage. The overall system consists of three controller 1) current controller with prediction 2) voltage controller and 3) proposed variable DC LINK controller. The variable DC LINK control technique using the LIDVR protects DC LINK from overflowing the input current. The simulation results are depicted in this paper to show the effect of this proposed system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 A
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• pp.64-66
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• 1993

This paper presents an efficient method to calculate voltage collapse point and to improve static voltage stability. To evaluate static voltage stability in power systems. it is necessary to get critical loading points. For this purpose, we use linear programming to calculate efficiently voltage collapse point. And if index value becomes larger than given threshold value, vol tags stability is improved by compensation of reactive power at selected bus. This algorithm is verified by simulation on the sample system.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2011년도 전력전자학술대회
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• pp.481-482
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• 2011

New discrete time domain models for the peak current controlled (PCC) power LED drivers in continuous conduction mode include for the first time the effects of time delay in the pulse-width-modulator. Realistic amounts of time delay are found to have significant effects on the average output LED current and on the critical inductor value at the boundary between two conduction modes. Especially, the time delay can provide an accurate LED current for the PCC buck converter with a wide input voltage. The models can also predict the critical inductor values at the mode boundary as functions of the input voltage and the time delay.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.662_663
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• 2009

Motor bus transfer involves the process of transferring a bus that has several critical motors to an alternate source of power when the main normal power source feeding them is interrupted. Bus transfer is a time-critical application in which the transfer progress depends on various parameters such as the type of motor, load on the motor at the time of transfer, inertia of the motor, and the combined open-circuit time constant of various motors present on the bus at the time of transfer. This paper present the result of modeling and simulation of nuclear power motor bus using ETAP(Electrical Transient Analyzing Program) program for motor and motor bus residual voltage decay characteristics.

• 전력전자학회논문지
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• 제21권3호
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• pp.200-206
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• 2016

In the microgrid, inverters for energy storage system are generally constructed in a parallel structure because of capacity expandability, convenience of system maintenance, and reliability improvement. Parallel inverters are required to provide stable voltage to the critical load in PCC and to accurately share the current between each inverter. Furthermore, when islanding occurs, the inverters should change its operating mode from grid-connected mode to stand-alone mode. However, during clearing time and control mode change, the conventional control method has a negative impact on the critical load, that is, severe fluctuating voltage. In this study, a parallel operation control method is proposed. This method provides seamless mode transfer for the entire transition period, including clearing time and control mode change, and has accurate current sharing between each inverter. The proposed control method is validated through simulation and experiment.

• 전자공학회논문지
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• 제54권3호
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• pp.138-144
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• 2017

본 논문에서는 노인성 난청으로 인한 청력도 감쇄를 보상하는 고주파 증폭 회로를 제안한다. 노인성 난청은 고음역(고주파 대역)의 청력도가 저음역(저주파대역)에 비해 더 떨어지는 저주파 통과 필터의 특성을 보이므로, 보상회로는 임계주파수 이상의 대역에서는 주파수에 비례하여 신호를 증폭하고 임계주파수 이하에서는 증폭도를 일정하게 유지하는 구조이다. 제안된 고주파 회로는 미분기, 단위 이득 증폭기로 구성된다. 임계주파수는 볼륨 조절 레버 형태로 간단하게 제어가 가능한 구조로 노인들이 자신의 난청정도에 따라 쉽게 증폭도를 조절할 수 있다. 고주파 증폭회로의 임계주파수는 가청주파수 전 대역에서 연속적으로 조절 가능하고, 10 kHz 음역의 신호는 80dB 이상 증폭도를 가진다.

• Journal of Power Electronics
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• 제16권1호
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• pp.351-361
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• 2016

Power quality is a critical issue in distribution systems, where a dynamic voltage restorer (DVR) is commonly used to mitigate the voltage disturbances for loads. This paper deals with a nonlinear control for the three-phase four-wire (3P-4W) DVR under a grid voltage unbalance and nonlinear loads in the distribution system, where a novel control scheme based on the feedback linearization technique is proposed. Through feedback linearization, a nonlinear model of a DVR with a PWM voltage-source inverter (VSI) and LC filters is linearized. Then, the controller design of the linearized model is performed by applying the linear control theory, where the load voltages are kept constant by controlling the d-q-0 axis components of the DVR output voltages. To keep the load voltage unchanged, an in-phase compensation strategy is employed, where the load voltages are recovered to be the same as the previous voltage without a change in the magnitude. With this strategy, the performance of the DVR becomes faster and more stable even under unbalanced source voltages and nonlinear loads. The validity of the proposed control strategy has been verified by simulation and experimental results.