• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권11호
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• pp.647-657
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• 2004

Helical magneto-cumulative generator(HMCG)s are very useful devices in suppling pulsed high current to inductance loads. To apply fast high voltage pulses to high impedance loads, high current outputs of HMCGs are required to be conditioned to higher voltages by using various pulse components such as opening/closing switches and pulse transformer. In this paper, stepping with the trends of requirements for ever-increasing energy in pulsed power applications coupling methods is investigated to obtain higher output energy by connecting several HMCGs in series or parallel way. The coil dimension of HMCGs used in series or parallel connections was 50 mm in diameter and 150 mm in length. The coil was fabricated by using enamel-coated copper wire of 1 mm in diameter. The highest energy amplification ratio and peak voltage of load were achieved from the serially connected four-barrel HMCG system. They were 68 and 34 kV, respectively, when the initial energy of 0.36 kJ was supplied into that system with the load of 0.4 μH. Within the tested range of inductance ratio, energy amplification ratio was found to be highly dependent on the inductance ratio of serial- and parallel-connected HMCG systems to load, which to be optimal around 500 was turned out. The experimental results showed that the output energy and voltage of load are controlled by connecting HMCGs in series or parallel.

• Journal of Power Electronics
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• 제15권2호
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• pp.389-398
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• 2015

This paper presents a 1.92 kW resonant converter for medium voltage applications that uses low voltage stress MOSFETs (500V) to achieve zero voltage switching (ZVS) turn-on. In the proposed converter, four MOSFETs are connected in series to limit the voltage stress of the power switches at half of the input voltage. In addition, three resonant circuits are adopted to share the load current and to reduce the current stress of the passive components. Furthermore, the transformer primary and secondary windings are connected in series to balance the output diode currents for medium power applications. Split capacitors are adopted in each resonant circuit to reduce the current stress of the resonant capacitors. Two balance capacitors are also used to automatically balance the input capacitor voltage in every switching cycle. Based on the circuit characteristics of the resonant converter, the MOSFETs are turned on under ZVS. If the switching frequency is less than the series resonant frequency, the rectifier diodes can be turned off under zero current switching (ZCS). Experimental results from a prototype with a 750-800 V input and a 48V/40A output are provided to verify the theoretical analysis and the effectiveness of the proposed converter.

• 전력전자학회논문지
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• 제19권1호
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• pp.23-30
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• 2014

This paper proposes a single power-conversion ac-dc converter with a dc-link capacitor-less and high power factor. The proposed converter is derived by integrating a full-bridge diode rectifier and a series-resonant active-clamp dc-dc converter. To obtain a high power factor without a power factor correction circuit, this paper proposes a suitable control algorithm for the proposed converter. The proposed converter provides single power-conversion by using the proposed control algorithm for both power factor correction and output control. Also, the active-clamp circuit clamps the surge voltage of switches and recycles the energy stored in the leakage inductance of the transformer. Moreover, it provides zero-voltage turn-on switching of the switches. Also, a series-resonant circuit of the output-voltage doubler removes the reverse-recovery problem of the output diodes. The proposed converter provides maximum power factor of 0.995 and maximum efficiency of 95.1% at the full-load. The operation principle of the converter is analyzed and verified. Experimental results for a 400W ac-dc converter at a constant switching frequency of 50kHz are obtained to show the performance of the proposed converter.

• Transactions on Electrical and Electronic Materials
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• 제18권2호
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• pp.97-102
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• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.2021_2022
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• 2009

Partial discharges(PD) is a important factor to evaluate the insulation state in high voltage electric machinery. However, measuring PD under the circumstances of power plant is occasionally impossible due to the relatively high magnitude of noise which is emanated from the operating machinery. In some case, the instrument measuring PD can not even perform a calibration that initializes tools and enhance the accuracy. This paper presents that we devised a noise reduction method and demonstrated the usefulness in acquiring reliable PD signals. We attached a series of filter and transformer at the input of power source of the instruments which refrains high noise signals from incoming to the instruments. We experimented the efficiency of noise reduction applying the device into the Dangjin Power Plant and Factory. As a result of testing with the filter and transformer, we can easily calibrate the PD signal compared to the case without the device. Additionally, we can detect the small PD signal which was unperceived with a normal device.

• 조명전기설비학회논문지
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• 제26권9호
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• pp.47-56
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• 2012

This research is to develop satiable battery charger with a variety of capacity and voltage specifications of battery. For this, voltage or current were controlled through buck converter which is DC voltage that already received three-phase at primary side and passed bridge rectifier diode. And, it was comprised of full-bridge converter and HFTR for insulation and a square wave AC. The transformer primary side was comprised in series to divide certain charging current and the secondly side was comprised of 6 fixed transformers so that they can generate certain amount of power and various output voltage through relay parallel compound 6 DC Link outputs. To confirm such structure's verification and validity, simulation with PSIM was conducted, and validity of proposed variable charger system was verified through 3kW stack production.

• 전력전자학회논문지
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• 제18권2호
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• pp.153-160
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• 2013

This research paper describes the development of battery charger with a variable output voltage capacity for charging the batteries used in electrical vehicles. The voltage and current accordingly is control via the buck converter that receives three phase current at primary side and fed to bridge rectifier which is comprised of full bridge converter and HFTR(High Frequency Transformer) for isolation and a square wave AC output. The transformer primary side is in series to divide certain charging current and the secondary side is comprised of six fix transformers so that they can generate certain amount of power and various output voltage through relay connection using 6 DC outputs. Moreover, all parallel connected full bridge serial resonant converter communicate together with upper(main) controller. The constructed structure is verified by conducting the test on PSIM as well as experimentally.

• Journal of Electrical Engineering and Technology
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• 제9권4호
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• pp.1296-1308
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• 2014

This paper presents a new zero voltage switching (ZVS) converter for medium power and high input voltage applications. Three three-level pulse-width modulation (PWM) circuits with the same power switches are adopted to clamp the voltage stress of MOSFETs at $V_{in}/2$ and to achieve load current sharing. Thus, the current stresses and power ratings of transformers and power semiconductors at the secondary side are reduced. The resonant inductance and resonant capacitance are resonant at the transition interval such that active switches are turned on at ZVS within a wide range of input voltage and load condition. The series-connected transformers are adopted in each three-level circuit. Each transformer can work as an inductor to smooth the output current or a transformer to achieve the electric isolation and power transfer. Thus, no output inductor is needed at the secondary side. Three center-tapped rectifiers connected in parallel are used at the secondary side to achieve load current sharing. Compared with the conventional parallel three-level converters, the proposed converter has less switch counts. Finally, experiments based on a 1.44kW prototype are provided to verify the operation principle of proposed converter.

• 조명전기설비학회논문지
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• 제19권5호
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• pp.23-29
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• 2005

비선형 부하의 증가는 변압기에 고조파 전류를 증가시키는 요인이 되고 있다. 변압기에 고조파 전류가 유입되면 손실이 증가되고, 변압기 출력이 감소되어야 한다. 본 논문에서는 고조파를 고려한 부하의 변압기 용량 산정법을 제시하고, 직렬리액터가 연결된 커패시터 뱅크와 고조파 필터의 적용으로 변압기 출력을 증가시킬 수 있음을 검증하였다. 사례연구의 시뮬레이션은 EDSA 프로그램을 사용하였다.

• 조명전기설비학회논문지
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• 제12권4호
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• pp.136-145
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• 1998

본 논문에서는 몰드변압기 예방진단을 위해 정상상태와 비정상상태 몰드변압기의 진동신호의 FFT 및 시계열 분석에 관해 연구하였다. 실험올 위한 제어변수들로 공급전압, 부하전류 및 주위온도를 변화시키면서, 진동신호 크기, 주파수 스펙트럼 및 시계열 계수와 같은 측정변수들을 분석하였다. 제어변수 변화에 의한 진동선호는 권선표변과 철섬에 부착된 가속도센서로 측정되었으며, 이 신호들은 중폭기를 거쳐 데이터 수집장치에서 측정변수들로 계산되었다. 또한, 정 상상태 분석 후, 몰드변압기의 구조적 변형올 모의하였다. 비정상상태 진동신호는 정상상태와 같은 제어변수 변화 에 의해 측정되었다. 연구 결과, 정상상태와 비정상상태 진동신호는 수직진동신호와 수평진동신호를 비교하여 분석함으혹써 구별이 가능하였다.