• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.921-928
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• 2011

This paper presents a new method of local voltage control to achieve coordinative control among UPFC(Unified Power Flow Controller) and conventional reactive compensation equipments, such as switched-shunt and ULTC(Under-Load Tap Changing) transformer. Reactive power control has various difficult aspects to control because of difficulty of system analysis. Recently, the progress of power electronics technologies has lead to commercial availability of several FACTS(Flexible AC Transmission System) devices. The UPFC(Unified Power Flow Controller) simultaneously allows the independent control of active and reactive power flows as well as control of the voltage profile. When conventional reactive power sources and UPFC are used to control system voltage, the UPFC reacts to the voltage deviation faster than the conventional reactive power sources. Keeping reactive power reserve in an UPFC during steady-state operation is always needed to provide reactive power requirements during emergencies. Therefore, coordination control among UPFC and conventional reactive power sources is needed. This paper describe the method to keep or control the voltage of power system of local area and to manege reactive power reserve using PSS/E with Python. The result of simulation shows that the proposed method can control the local bus voltage within the given voltage limit and manege reactive power reserve.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1471-1483
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• 2017

The low-frequency characteristics of four-switch three-phase (FSTP) inverter are investigated in this paper. Firstly, a general space vector pulse width modulation (SVPWM) directly involved the neutral point voltage of DC-link is proposed, where no sector identifications and trigonometric function calculations are needed. Subsequently, to suppress the DC offset in the neutral point voltage, the relationship between the neutral point voltage and the ${\beta}-axis$ component of the load current is derived, and then a new neutral point voltage control scheme is proposed where no low pass filter is adopted. Finally, the relationship between the load power factor and the maximum linear modulation index of the FSTP inverter is revealed. Since the operational region for the FSTP inverter in low frequency is reduced by the enlarged amplitude of the neutral point voltage, a linear modulation range enlargement scheme is proposed. A permanent magnet synchronous motor with preset rotary speed serves as the low-frequency load of the FSTP inverter. Experimental results verify that the new neutral point voltage control scheme is effective in the deviation suppression of the neutral point voltage, and the proposed scheme is able to provide a larger linear operational region in low frequency.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.8
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• pp.405-412
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• 2003

This paper presents a three-phase Line-Interactive uninterruptible power supply (UPS) system with series-parallel active power-line conditioning capabilities, using synchronous reference frame (SRF) based controller, which allows an effective power factor correction, source harmonic voltage compensation, load harmonic current suppression, and output voltage regulation. The three-phase UPS system consists of two active power compensator topologies. One is a series active compensator, which works as a voltage source in phase with the source voltage to have the sinusoidal source current and high power factor under the deviation and distortion of the source voltage. The other is a parallel active compensator which works as a conventional sinusoidal voltage source in phase with the source voltage, providing to the load a regulated and sinusoidal voltage with low THD (total harmonic distortion). The control algorithm using SRF method and the active power flow through the Line-interactive UPS systems are described and studied. The simulation and experimental results are depicted in this paper to show the effect of the proposed algorithm.

• Journal of Power Electronics
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• v.16 no.1
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• pp.329-339
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• 2016

Owing to mismatched feeder impedances in an islanded microgrid, the conventional droop control method typically results in errors in reactive power sharing among distributed generation (DG) units. In this study, an improved droop control strategy based on secondary voltage control is proposed to enhance the reactive power sharing accuracy in an islanded microgrid. In a DG local controller, an integral term is introduced into the voltage droop function, in which the voltage compensation signal from the secondary voltage control is utilized as the common reactive power reference for each DG unit. Therefore, accurate reactive power sharing can be realized without any power information exchange among DG units or between DG units and the central controller. Meanwhile, the voltage deviation in the microgrid common bus is removed. Communication in the proposed strategy is simple to implement because the information of the voltage compensation signal is broadcasted from the central controller to each DG unit. The reactive power sharing accuracy is also not sensitive to time-delay mismatch in the communication channels. Simulation and experimental results are provided to validate the effectiveness of the proposed method.

• Journal of radiological science and technology
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• v.37 no.1
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• pp.1-6
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• 2014

Breast shooting performance management and quality control of the generator is applied to the amount of current IEC(International Electrotechnical Commission) 60601-2-45 tube voltage and tube current are based on standards that were proposed in the analysis of the test results were as follows. Tube voltage according to the value of the standard deviation by year of manufacture from 2001 to 2010 as a 42-3.15 showed the most significant, according to the year of manufacture by tube amperage value of the standard deviation to 6.38 in the pre-2000 showed the most significant, manufactured after 2011 the standard deviation of the devices, the PAE(Percent Average Error) was relatively low. This latest generation device was manufactured in the breast of the tube voltage and tube diagnosed shooting the correct amount of current to maintain the performance that can be seen. The results of this study as the basis for radiography diagnosed breast caused by using the device's performance and maintain quality control, so the current Food and Drug Administration "about the safety of diagnostic radiation generator rule" specified in the test cycle during three years of self-inspection radiation on a radiation generating device ensure safety and performance of the device using a coherent X-ray(constancy) by two ultimately able to keep the radiation dose to the public to reduce the expected effect is expected.

• Journal of Power Electronics
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• v.13 no.2
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• pp.243-249
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• 2013

This paper presents a neutral-point voltage balancing method for three-level inverter systems using a time-offset estimation scheme. The neutral-point voltage is balanced by adding a time-offset to the turn-on time of the switches. If an inaccurate time-offset is added, the neutral-point deviation still remains. An accurate time-offset is obtained through the proposed time-offset estimation scheme. This method is implemented without additional hardware, complex calculations, or analysis. The effectiveness of the proposed method is verified by experiments.

• Proceedings of the KIEE Conference
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• 1991.11a
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• pp.31-34
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• 1991

This paper presents a voltage-reactive power control algorithm considering fuzziness. In this paper, a coordination technique based on fuzzy set theory is applied for system loss-voltage compromises. Here, we introduce membership functions to measure the adaptability of real power loss of transmission line and the deviation of load bus voltage from the constraints. Then the optimization of problem is solved by a linear programming technique considering the fuzzy set theory. The objective is a degree of satisfaction about the fuzzy decision-making function. The effectiveness of this algorithm has been verified by testing on sample systems.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1523-1525
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• 1994

This paper describes a proposed very fast transient overvoltages(VFTO) measurement system suited for established gas insulated switchgear(GIS). The detecting system consists of a shield electrode connected to a buffer amplifier, and the transmission of the detected signal to an oscilloscope is made through an optical fiber. The bandwidth of the measurement system is 5 Hz to 30MHz. When determining the voltage dividing ratio by use of the commercial frequency voltage, the error is less than 0.5 %. Also, the data were obtained by the electric field probe and the high voltage probe, and their deviation for voltage dividing ratio were less than 1 %.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.1
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• pp.145-150
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• 2013

This paper has presented the analysis for threshold voltage and drain induced barrier lowering among short channel effects occurred in subthreshold region for double gate(DG) MOSFET as next-generation devices, based on scaling theory. To obtain the analytical solution of Poisson's equation, Gaussian function has been used as carrier distribution to analyze closely for experimental results, and the threshold characteristics have been analyzed for device parameters such as channel thickness and doping concentration and projected range and standard projected deviation of Gaussian function. Since this potential model has been verified in the previous papers, we have used this model to analyze the threshold characteristics. As a result to apply scaling theory, we know the threshold voltage and drain induced barrier lowering are changed, and the deviation rate is changed for device parameters for DGMOSFET.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.1
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• pp.163-168
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• 2015

This paper analyzed the deviation of tunneling current for bottom gate voltage of sub-10 nm asymmetric double gate MOSFET. The asymmetric double gate MOSFET among multi gate MOSFET developed to reduce the short channel effects has the advantage to increase the facts to be able to control the channel current, compared with symmetric double gate MOSFET. The increase of off current is, however, inescapable if aymmetric double gate MOSFET has the channel length of sub-10 nm. The influence of tunneling current was investigated in this study as the portion of tunneling current for off current was calculated. The tunneling current was obtained by the WKB(Wentzel-Kramers-Brillouin) approximation and analytical potential distribution derived from Poisson equation. As a results, the tunneling current was greatly influenced by bottom gate voltage in sub-10 nm asymmetric double gate MOSFET. Especially it showed the great deviation for channel length, top and bottom gate oxide thickness, and channel thickness.