• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.5
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• pp.936-943
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• 2009

Dynamic voltage restorer(DVR) is now more preferable enhancement than other power quality enhancement in industry to reduce the impact of voltage faults, especially voltage sags to sensitive loads. The main controllers for DVR consists of PLL(phase locked loop), compensation voltage calculator and voltage compensator. PLL detects the voltage faults and phase. Compensation voltage calculator calculates the reference voltage from the source voltage and phase. With calculated compensation voltage from PLL, voltage compensator restores the source voltage. If PLL detect ideal phase, compensation voltage calculator calculates ideal compensation voltage. Therefore, PLL for DVR is very important. This paper proposes the new method of PLL in DVR. First, the power circuit of DVR system is analyzed in order to compensate the voltage sags. Based on the analysis, new PLL for improving transient response of DVR is proposed. The proposed method uses band rejection filter(BRF) at q-axis in synchronous flame. In order to calculate compensation voltage in commercial instruments, the PQR theory is used. Proposed PLL method is demonstrated through simulation using Matlab-Simulink and experiment, and by checking load voltage, confirms operation of the DVR

• Proceedings of the KIPE Conference
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• 2009.11a
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• pp.287-289
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• 2009

This paper deals with a parallel processing uninterruptible power supply (UPS) for sudden voltage fluctuation in computer applications to integrate power quality improvement, load voltage stabilization and UPS. To reduce the complexity, cost and number of power conversions, which results in higher efficiency, only one voltage-controlled voltage source inverter (VCVSI) is used. The system provides sinusoidal voltage at the fundamental value of 220V/60Hz for the load during abnormal utility power conditions or grid failure. Also, the system can be operated to mitigate the harmonic current and voltage demand from nonlinear loads and provide voltage stabilization for loads when sudden voltage fluctuation occur, such as sag and swell. System operation simulation demonstrates that the system protects against outages caused by abnormal utility power conditions and sudden voltage fluctuations and changes.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.954-955
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• 2008

In this paper, the voltage harmonics are investigated in terms of the voltage sag versus the time constants of electric machinery under the source voltage variation condition. The electric machinery and compensation equipment are established on the proposed design scheme based on voltage quality effect assessment technology. It have been analyzed how the variation of harmonic order, the output current, the DC-Link voltage and the induction motor speed is carried out under the voltage sag and switching frequency variation.

• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.458-459
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• 2010

일반적으로 전력 품질을 저하시키는 여러 문제들 중에서 가장 빈도가 높고 민감한 부하를 가지고 있는 수용가에 많은 영향을 주고 있는 것이 순간적인 전압상승(voltage swell)과 전압 강하(voltage sag)인데, 순간 전압 강하는 짧은 시간 동안 공급 전압의 크기가 줄어드는 것으로 대부분 인접한 배전 선로에서의 사고가 그 원인으로 작용한다. 이러한 순간 전압 강하는 제조공정의 제어를 위한 자동화 기기 등의 오동작이나 작업정지 등의 문제를 유발하여 경제적으로 큰 손실을 일으키게 되는데 이러한 순간 전압 강하의 문제를 해결하기 위한 대표적인 전력 전자 기기로는 일반적으로 동적 전압 보상기(Dynamic Voltage Restore: DVR)가 있다. 본 논문에서는 새로운 3상 Quasi Z-소스 DVR을 제안하였다．

• Journal of the Korean Solar Energy Society
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• v.33 no.1
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• pp.66-72
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• 2013

In this study, the thermal conductive characteristics and basic properties of the nine commercial products of bentonite grouts were studied. Six of the nine products for ground heat exchanger systems are imported and others for civil engineering are domestic. The thermal conductivities of all bentonite products are nearly similar among products. The free swell indexes, viscosities and filter losses of the ground heat exchanger grouts are lower than those of the civil engineering ones. These characteristics seem to increase of the fluidity to fill the bentonite slurry to bore-hall perfectly, rather than to prevent underground water penetration. Thus, the mixtures of bentonites and sands are recommended for high thermal conduction grouts.

• Proceedings of the KIEE Conference
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• 1999.07a
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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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.2
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• pp.199-208
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• 2012

This paper proposes a quasi Z-source DVR(Dynamic Voltage Restorer) system with a series connection of the output terminals, to compensate the voltage variations in the 6.6[kV]/60[Hz] power distribution system. The conventional DVR using one quasi Z-source AC-AC converter has the advantage which it can compensate the voltage variations without the need for the additional energy storage device such as a battery, but it is impossible to compensate for the 50[%] under voltage sags. To solve this problem, a DVR system using two quasi Z-source AC-AC converters with the series connection of the output terminals is proposed. By controlling the duty ratio D in the buck-boost mode, the proposed system can control the compensation voltage. For case verification of the proposed system, PSIM simulation is achieved. As a result, in case that the voltage sags-swells occur 10[%], 20[%], 60[%] in power distribution system, and, in case that the 50[%] under voltage sags-swells continuously occur, all case could compensate by the proposed system. Especially, the compensated voltage THD was examined under the condition of the 10[%]~50[%] voltage sags and the 20[${\Omega}$]~100[${\Omega}$] load changes. The compensated voltage THD was worse for the higher load resistances and more severe voltage sags. Finally, In case of the voltage swells compensation, the compensation factor has approached nearly 1 regardless of the load resistance changes, while the compensation factor of voltage sags was related to the load variations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.12
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• pp.1792-1797
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• 2013

Recently, due to the excessive use of fossil fuels, many studies about the fossil fuels such as solar and fuel cell energy source are progressing. Fuel cell system has high energy conversion efficiency. Also, fuel cell system is environmentally friendly system because the carbon emission is almost not occur. Therefore, the fuel cell system is considered as the core technology of in the fields of the future energy and environmental. Fuel cell system has an effect on distribution power system because another power source of other than large power plants. So, fuel cell system can be reason of power quality in the power system. In this paper, we constructed the system for an assessment on Islanding. The system is composed with power source, Impedance coordination load and linear load, fuel cell system. we are performed assessment on voltage and power quality in customer and the distributed power system during the Islanding of residential fuel cell system. In addition, no change in the impedance of power system, we made a islanding condition only using the actual load, As a variation of generation and load current under islanding, an analysis results based on assessment system showed that the power qualities of distribution system became more aggravation as effect of voltage sag and voltage swell phenomena.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.1
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• pp.96-101
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• 2010

Superconducting Magnetic Energy Storage (SMES) system is one of the key technologies to overcome the voltage sag, swell, interruption and frequency fluctuation by fast response speed of current charge and discharge. In order to evaluate the characteristics of over mega joule class grid connected High Temperature Superconducting (HTS) SMES system, the authors proposed an algorithm by which the SMES coil could be connected to the Real Time Digital Simulator (RTDS). Using the proposed algorithm, users can perform the simulation of voltage sag and frequency stabilization with a real SMES coil in real time and easily change the capacity of SMES system as much as they need. To demonstrate the algorithm, real charge and discharge circuit and active load were manufactured and experimented. The results show that the current from real system was well amplified and applied to the current source of simulation circuit in real time.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.601_602
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• 2009

Superconducting Magnetic Energy Storage (SMES) system is one of the key technologies to overcome the voltage sag, swell, interruption and frequency fluctuation by fast response speed of current charge and discharge. In order to evaluate the characteristics of over mega joule class grid connected High Temperature Superconducting (HTS) SMES system, the authors proposed an algorithm by which the SMES coil could be connected to the Real Time Digital Simulator (RTDS). Using the proposed algorithm, users can perform the simulation of voltage sag and frequency stabilization with a real SMES coil in real time and easily change the capacity of SMES system as much as they need. To demonstrate the algorithm, real charge and discharge circuit and active load were manufactured and experimented. The results show that the current from real system was well amplified and applied to the current source of simulation circuit in real time.