• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.4
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• pp.237-243
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• 2019

A high-efficiency and small-sized switched-mode line transformer (SMLT) is proposed in this study. The conventional structure of an adapter is composed of line transformer and rectifiers. This structure has a limit in miniaturizing due to low-frequency line transformer. Another structure is composed of power factor correction (PFC) and DC/DC converter. This structure has a limit in reducing volume due to two-stage structure. As the proposed SMLT is composed of an LLC resonant converter, a high-frequency transformer can be adopted to achieve isolation standards and size reduction. This proposed structure has different operation modes in accordance with line input voltage to overcome poor line regulation. In addition, the proposed SMLT is applied to the front of a conventional PFC converter, because the SMLT output voltage is restored to rectified sinusoidal wave by using a full-bridge rectifier in the secondary side. The design of the PFC converter is easy, because the SMLT output voltage is controlled as rectified sinusoidal wave. The validity of the proposed converter is proven through a 350 W prototype.

• Journal of Electrical Engineering and Technology
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• v.8 no.5
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• pp.1070-1077
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• 2013

Owing to the consistent increase in energy efficiency issues, studies for improving regenerative energy utilization have been receiving attention in the Urban DC railway systems, where currently, the utilization of regenerative energy is low due to the lack of a specific plan for using this energy. The regenerative energy in railway systems has a low efficiency problem which results in the increase of the catenary voltage and a possibility to create problems to the electrical devices connected to the system. This paper deals with the power integration of large urban railway subsystems to improve regenerative energy utilization where the railway subsystems are integrated with other railway subsystems to improve the energy efficiency. Through the case studies, to find the realistic effect of integrated operation, the Seoul Metro subsystems, namely Line 5 and Line 7, has been applied. Also, evaluation for the electricity cost saving has been performed by using KEPCO electricity cost table.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.1
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• pp.44-51
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• 2005

In this paper, reduction characteristics of the AC and DC flashover voltage in the horizontal air gap of sphere-sphere electrode system were investigated when the combustion flame was present near the high voltage electrode. The voltage and current waveforms were measured, when the flashover is occurred, in order to examine the flashover polarity by flame. The reduction characteristics of AC flashover voltage were discussed with the thermal ionization process, the relative air density and the deflection phenomena in the shape of flames that caused by the coulomb's force. As the results of an experimental investigation, It was found that the reduction of flashover voltages in sphere-sphere system, in comparison with the no flame case, are $79.9[\%]$ for k=0, $82.9[\%]$ for k=0.5, $87.5[\%]$ for k=1.0, $85.0[\%]$ for h=0[cm], $40.8[\%]$ for h=5[cm] and $28.2[\%]$ for h=9[cm] when ac voltage is applied. The influence for thermal ionization process of the combustion flame in small scale no particular change is recognized.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.1
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• pp.36-41
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• 2011

Medical X-ray has been brought many changes according to the rapid development of high technology. Especially, for high-voltage generator which is the most important in X-ray generation the traditional way is to use high-voltage electric transformers primarily. However, since it is large and heavy and the ripple rate of DC high-voltage applied to X-ray tube is too big, it has a disadvantage of low X-ray production efficiency. To solve these problems, the studies about high-voltage power supply are now proceeding. At present, the high-voltage generator that generates high-voltage by making high frequency using inverter control circuit consisting of semiconductor device is mainly used. High-voltage generator using inverter has advantages in the diagnosis using X-ray including high performance with short-term use, miniaturization of power supply and ripple reduction. In this study, the X-ray high-voltage device with inverter type using pulse width modulation scheme to the control of tube voltage and tube current was designed and produced. For performance evaluation of produced device, the control signal analysis, irradiation dose change and beam quality depending on the load variation of tube voltage and tube current were evaluated.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.4
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• pp.22-27
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• 2004

The gas discharge AND gate which have been newly proposed is applied to three electrode surface discharge AC PDP. The address discharge characteristics by the DC-AC floating discharge by which Y electrode is made floating electrode is analyzed The address discharge can be begun by using the floating discharge from the experiment result Moreover, the display discharge can be sustained. The DC priming discharge that the floating discharge is matched to timing is generated in a supplementary electrode. As a result, space charge is supplied enough to the space of the floating discharge and the data voltage is lowered up to l00(V). Driving method to use this DC-AC floating discharge is able to obtain the address operation margin of l00(V).

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.3
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• pp.82-92
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• 1999

In this paper, we realize the active PFC(Power Factor Correction) system of the BF(Boost Forward) converter with the PWM-PFM control technique to control DC output voltage, to rermve the noise like hanronics at the output voltage, amd to control the input ClUTent with sinusoidal wave synchronized by the source voltage. We take the simulation and analyze the switching signal of the BF converter, input/output voltage and current, its harmonics and power factor through PSpice. And it has bren obtained harmonic reduction and efficiency improverrent.errent.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.4
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• pp.196-200
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• 2004

This paper presents a method to reduce the commutation torque ripple in a position sensorless brushless DC motor drive. To compensate the commutation torque ripple considerably, the duration of commutation must be known. The proposed method measures the duration of commutation from the terminal voltage of the motor, calculates a PWM duty ratio using the measured commutation interval to suppress the commutation torque ripple, and applies it to the calculated PWM duty ratio only during the next commutation. Experimental results show that pulsating currents and vibrations are considerably reduced when the proposed method is applied to a position sensorless brushless DC motor drive for the air-conditioner compressor.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.3
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• pp.199-205
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• 1998

Brushless DC motors have trapezoidal back-EMF waveform. Theoretically it should be fed with rectangular phase current in order to produce torque ripple free. Because it is drived by a voltage source inverter, perfect rectangular phase current can not available and therefore produce torque ripple. In this paper, the torque ripple due to commutation is analyzed and the practical method that can reduce the torque ripple is proposed. Experimental and simulation results show the effectiveness of the proposed method.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.1
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• pp.77-83
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• 2012

In this paper, an optimal solution to the harmonic reduction problem in a cascaded multilevel inverter with non-equal DC sources using a genetic algorithm (GA) is presented. Switching angles are generated for different values of modulation index by the proposed algorithm, considering minimum voltage total harmonic distortion (THD) whereas selected harmonics are controlled within the allowable limits at all desired modulation indices including the point of discontinuity. Results are stored as a look-up table to be used to control the inverter for a certain operating point. The computed angles are used in a simulated circuit in Matlab\Simulink to validate the results.

• Journal of IKEEE
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• v.24 no.3
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• pp.867-876
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• 2020

This paper proposes a neutral-point voltage ripple reduction of high frequency injection sensorless control of IPMSM fed by a three-level inverter. The high frequency voltage injection method has been successfully applied to sensorless control for IPMSM at low speed region. In the process of high frequency voltage injection sensorless control for IPMSM, the neutral-point voltage ripple is increased. It should be reduced because it distorts the output current and decreases a life time of DC-link capacitor. The proposed method in this paper reduces the neutral-point voltage ripple by compensating the reference voltage, and the compensation value is calculated simply with reference voltages and currents. The effectiveness of the proposed method is verified by simulation results.