• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.5
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• pp.96-104
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• 2004

This paper proposes a dc power regenerating systems, which can generate the excessive dc power from dc bus line to ac supply in substations for traction system The proposed regeneration inverter system for dc traction can be used as both an inverter and an active power filter(APF). As an regeneration inverter mode, it can recycle regenerative energy caused by decelerating tractions and as an active power filter mode, it can compensate for harmonic distortion produced by the rectifier substation. From the viewpoint of both power capacity and switching losses, the system is designed on the basis of three phase PWM inverters and composed of parallel inverters, output transformers, and an LCL filter.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1782-1789
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• 2008

This paper presents the design of acoustic resonance(AR) free and dimmable electronic ballast for 1kW Metal-Halide Lamp(MHL). The proposed Ballast consists of a Full-Bridge(FB) rectifier, a passive power factor correction(PFC) circuit, a full-bridge inverter, an ignitor using LC resonance and a control circuit for frequency modulation and dimming control. Whereas a passive PFC provides advantages in terms of high reliability and low cost for constructing the circuit, it is difficult to supply a stable voltage because of the output voltage ripple that occurs with a period of 120Hz. Although the ballast can be designed with a small size and a light weight if it is driven at a switching frequency between 1 and 100 kHz, AR will occur if the eigenvalue frequency of the lamp coincides with the inverter's operation frequency. The operation frequency was modulated in real time according to the output voltage ripple to compensate for the variation in power supplied to the lamp and eliminate AR. For dimming, the method, which modulated drive frequency of FB inverter using the control of DC level by microprocessor, was used. The Dimming ranged at least from 600W to 1kw as rated power of the lamp with 4 stages. Performance of the proposed technique was validated through numerical analysis, computer simulation using Pspice and by applying it to an electronic ballast for a prototype 1kW MHL.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.1
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• pp.121-126
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• 2013

Cycloconverter used as a power conversion device in the speed and torque control system of AC machines has the advantage of a simple control and a large torque at low speed. In addition, because a rectifier, a DC link, and an inverter are not installed, this system is simple and suitable for large power system. If a power conversion device, which is currently used as a propulsion motor of large vessel, is changed into cycloconverter, the system is simplified and then the installation costs can be significantly reduced. However, conventional cycloconverter has the increased harmonics because the power loss is large and the waveform of output voltage is distorted, due to the high-speed switching of power semiconductor devices. In order to improve these shortcomings, this paper describes a phase shifting filter which is composed of two inputs with different phases in the primary side and one output in the secondary one. As the voltage waveforms with two different phases are added and transformed into the secondary side, these outputs are close to sinusoidal waves. Thereby the voltage waveforms, which are applied to the propulsion motors, are improved and total harmonic distortions (THDs) are significantly reduced.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.2
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• pp.497-507
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• 2010

This paper presents current unbalance improved half-bridge LLC resonant converter using the two transformers with different leakage inductances. The proposed converter resonates with the leakage inductance and magnetizing inductance of the transformer and the resonant capacitance. The converter operates in a wide load range and satisfies the zero voltage switching even under the light load. The series-parallel connected two transformers act as the transformers or the resonant inductances according to the operational modes, and the separate output filter inductance in the transformer secondary is not needed using the leakage inductance. The current unbalance of the secondary diode rectifier is improved using the different leakage inductances of the two transformers and the asymmetrical pulse-width modulation (PWM). In this paper, the operational principle of the converter is explained by the modes, and the design example for the prototype is also shown. To validate the performance of the converter, the prototype is implemented as the designed circuit parameters and the good performance of the proposed converter is shown through the experimental results

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.3
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• pp.75-84
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• 2005

Since an unexpected fault of induction motor drive systems can cause serious troubles in many industrial applications, which the technique is required to diagnose faults of a voltage-fed PWM inverter for induction motor drives. The considered fault types are rectifier diodes, switching devices and input terminals with open-circuit faults, and the signal for diagnosis is derived from motor currents. The magnitude of dq-current trajectory is used for the feature extraction of a fault and PCA LDA are applied to diagnose. Also, we show results with respect to the execution time because of the possibility to use that a diagnosis software is embedded in the controllers of medium and small size induction motors drive for real-time diagnosis. After we performed various simulations for the fault diagnosis of the inverter, the usefulness of proposed algerian was verified.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1869-1883
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• 2016

In recent years, some converter structures and analyzing methods for the voltage regulation of stand-alone self-excited induction generators (SEIGs) have been introduced. However, all of them are concerned with the three-phase voltage control of three-phase SEIGs or the single-phase voltage control of single-phase SEIGs for the operation of these machines under balanced load conditions. In this paper, each phase voltage is controlled separately through separated converters, which consist of a full-bridge diode rectifier and one-IGBT. For this purpose, the principle of the electronic load controllers supported by fuzzy logic is employed in the two-different proposed converter structures. While changing single phase consumer loads that are independent from each other, the output voltages of the generator are controlled independently by three-number of separated electronic load controllers (SELCs) in two different mode operations. The aim is to obtain a rated power from the SEIG via the switching of the dump loads to be the complement of consumer load variations. The transient and steady state behaviors of the whole system are investigated by simulation studies from the point of getting the design parameters, and experiments are carried out for validation of the results. The results illustrate that the proposed SELC system is capable of coping with independent consumer load variations to keep output voltage at a desired value for each phase. It is also available for unbalanced consumer load conditions. In addition, it is concluded that the proposed converter without a filter capacitor has less harmonics on the currents.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.6
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• pp.798-802
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• 2013

In a conventional DC power supply used for CO2 laser, the circuit elements such as a rectifier bridge, a current-limiting resistor, a high voltage switch, energy storage capacitors ans a high-voltage isolation transformer using high turn ratio are necessary. Consequently, those supplies are expensive and require a large space. Thus, laser resonator and power supply should be optimally designed. In this paper, we propose a new power supply using high frequency resonance phenomena for CW(Continuous wave) CO2 laser (maximum output of 23W with discharge length of 450mm). It consists of a transformer including leakage inductance, magnetizing inductance and half-bridge converter, a three-stage Cockcroft-Walton and PFC(Power factor correction) circuit. The output ripple voltage can be controlled the minimum of 0.24% under the high frequency switching of 231kHz. Furthermore, the output efficiency was improved to 16.4% and the laser output stability of about 5.6% was obtained in this laser system.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.1
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• pp.1-7
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• 1998

Due to the increase in capacity of auxiliary machinery in power plant, the importance of energy saving has been greatly emphasized. If the speed of fans or pumps is controlled in accordance with the variation of load, large electric energy can be saved. Large capacity inverter, 2MVA GTO inverter, has been developed by operating two of 1MVA unit inverters in parallel. The parallel operation of the unit inverter is accomplished through two output transformers of which the secondary windings are connected in series. The system is composed of one control cubicle, one rectifier cubicle and 2 unit inverter cubicles. This inverter system was applied to the sea water lift pump(SLP) driven by a 6.6KV 1500KW induction motor in Seo-Inchon power plant to save the electric energy. The parallel operation of inverters by 180 degrees apart in switching frequency helps to reduce the harmonic components.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.213-215
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• 2018

본 논문에서는, 경부하 조건에서 저감된 스위칭 손실과 중부하 이상 조건에서 영전압 스위칭을 통해 높은 효율을 가지는 토템폴 브리지리스 역률보상회로를 제안한다. 토템폴 브리지리스 역률보상회로는 기존 브리지 다이오드를 포함한 역률보상회로의 단점인 도통패스 구간의 비교적 많은 소자 수를 통한 도통손실이 다소 큰 단점을 보완한 회로이다. 하지만, 토템폴 브리지리스 역률보상회로는 여전히 하드 스위칭을 통한 손실과 주 파워링 다이오드의 역회복 손실로 인한 단점을 지니고 있게 되며, 그로 인해 현재로써는 높은 효율과 안정적인 동작을 위해서는 부득이 GaN FET를 적용한 개발이 대부분이다. Full 부하 조건의 전류 용량을 고려하여 높은 전류 정격을 가지는 GaN FET를 주 스위치로 활용할 경우, 전류용량과 비례하여 기생 커패시턴스에 의한 손실이 커지기 때문에 경부하 조건에서 높은 효율을 확보하기가 다소 어렵다. 또한 구조상 물리적으로 여전히 하드 스위칭 동작을 할 수 밖에 없기 때문에 서버용 전원장치에서 요구하는 높은 효율을 달성하는데 한계를 지니며 높은 비용이 요구되는 단점을 지니게 된다. 이를 해결하기 위해, 제안하는 회로는 간단한 회로를 통해 경부하 조건에서 저감된 스위칭 손실과 중부하 이상 조건에서 소프트 스위칭을 만족하여 전체 부하 조건에서 기존의 GaN FET을 활용한 토템폴 구조 대비 높은 효율을 가지게 된다. 또한, 토템폴 구조임에도 불구하고 중부하 이상 영역에서 소프트 스위칭 동작을 통해 주 스위치를 비교적 저렴하고 신뢰성이 검증된 Si-MOSFET을 적용할 수 있다는 장점을 지닌다. 제안하는 회로의 효용성을 증명하기 위해, 하이라인 입력 전압과 750W 출력 조건에서 실험을 진행하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.4
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• pp.328-339
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• 2006

In this paper the characteristic analysis of a single-phase switched reluctance motor (SRM) drive system with power factor correction (PFC) circuit is presented. The SRM is a low cost, simple and has a good high speed performance. The SRM drive with diode rectifier and filter capacitor has a low power factor because of short switch on time of capacitor. A novel switching topologic is presented to improve power factor and reduce torque ripple based on analysis of PFC circuit. Accordingly the SRM drive system with PFC circuit is also presented. Through the numerical analysis of the system, the toque ripple, power factor and efficiency with the change of rotary speed, load torque and capacity of the capacitor are achieved and compared with actual measured value.