• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.4
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• pp.60-67
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• 2008

This paper presents a new full-bridge soft switching PWM DC-DC converter circuit topology that adding two switcher, two lossless snubber quasi-resonance capacity, two diode to power source for general welding machine. This half bridge soft switching Is low voltage hight current output that first coil current is smaller than second coil current in high frequency transformer can be obtained with decreasing path loss in conventional DC bus line switcher. As it operate ZCS/ZVS in full range, high frequency, high efficiency and high output are implemented at low voltage and high DC current switching power supplies. All of this items are got from simulation and the result of experiment. If make up for the weak points of this proposed circuit, it will be used more easily for next generation TIG, MIG and MAG type of arc-welding machine.

• Journal of Power Electronics
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• v.13 no.2
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• pp.206-213
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• 2013

In this paper, an improved passive snubber is investigated in a single-phase single-stage full-bridge boost power factor correction (PFC) converter, by which the voltage spike across primary side of the power transformer can be suppressed and the absorbed energy can be transferred to the output side. When compared with the basic passive snubber, the two single-inductors are replaced by a coupled-inductor in the improved snubber. As a result, synchronous resonances in the snubber can be achieved, which can avoid the unbalance of the voltage and current in the snubber. The operational principle of the improved passive snubber is analyzed in detail based on a single-phase PFC converter, and the design considerations of both the snubber and the coupled-inductor are given. Finally, a laboratory-made prototype is built, and the experimental results verify the feasibility of the proposed method and the validity of the theoretical analysis and design method.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.128-137
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• 2015

A novel parallel three-level zero voltage switching (ZVS) DC converter is presented for medium voltage applications. The proposed converter includes three sub-circuits connected in parallel with the same power switches to share load current and reduce the current stress of passive components at the output side. Thus, the size of the output chokes is reduced and the switch counts in the proposed converter are less that in the conventional parallel three-level DC/DC converter. Each sub-circuit combines one half-bridge converter and one three-level converter. The transformer secondary windings of these two converters are connected in series in order to reduce the size of output inductor. Due to the three-level circuit topology, the voltage stress of power switches is equal to $V_{in}/2$. Based on the resonant behavior by the output capacitance of power switches and the leakage inductance (or external inductance) at the transition interval, each switch can be turned on under ZVS. Finally, experiments based on a 2 kW prototype are provided to verify the performance of the proposed converter.

• Journal of Power Electronics
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• v.15 no.5
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• pp.1217-1226
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• 2015

In a grid-connected photovoltaic (PV) system, the traditional Z-source inverter uses a low frequency transformer to ensure galvanic isolation between the grid and the PV system. In order to combine the advantages of both Z-source inverters and transformerless PV inverters, this paper presents a modified single-phase transformerless Z-source PV grid-connected inverter and a corresponding PWM strategy to eliminate the ground leakage current. By utilizing two reversed-biased diodes, the path for the leakage current is blocked during the shoot-through state. Meanwhile, by turning off an additional switch, the PV array is decoupled from the grid during the freewheeling state. In this paper, the operation principle, PWM strategy and common-mode (CM) characteristic of the modified transformerless Z-source inverter are illustrated. Furthermore, the influence of the junction capacitances of the power switches is analyzed in detail. The total losses of the main electrical components are evaluated and compared. Finally, a theoretical analysis is presented and corroborated by experimental results from a 1-kW laboratory prototype.

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.200-202
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• 2006

We investigated the operating characteristics of a flux-lock type superconducting fault current limiters according to the number of the serial connection each the superconducting element at the additive polarity winding of a transformer. This SFCL consists of two coils wound in parallel on the same iron core, and the secondary coil is connected to the elements in series. Operating characteristics can be controlled by adjusting the inductances and the winding directions of the coils. It turns ratio between the primary and the secondary coils is 63:21. The analysis of voltage, current, and resistance in serial connection each element was performed to increase the applied voltage of flux-lock type SFCL. When the applied voltage was 200/$\sqrt{3}[V_{rms}]$ with three elements connected in seres, the peak value of the line current increased up to 26,24[A]. On the other hands, resistive SFCL increased up to 36.35[A], under the same conditions. This enabled the flux-lock type SFCL to be easy to increase the capacity of power system.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.8
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• pp.1278-1284
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• 2008

Electric propulsion motors are operated from a variable frequency drive, which supplies power to motors at a frequency appropriate to the desired speed. The objective of this study was to evaluate power converters for shipboard applications and to recommend converters that meet lower harmonic distortion levels and torque ripples. Two systems were studied in detail : Cyclo-converters and PWM-converters. Cyclo-converters are the obvious choice where size, weight and efficiency are the most critical issues. However they have a disadvantage in power factor and they produce severe torque ripples in the motor which makes them unacceptable without special systems. PWM-converters produces better motor current waveform and eliminates common mode voltage issues at the motor, but suffers a multiple stages of power conversion and the isolating transformer. Results of this case study show that PWM-converters are more advanced and efficient drives for induction motor of electric propulsion ship.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.301-303
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• 2001

In this paper we present a Capacitor Charging Power Supply (CCPS) using a series-resonant three-level inverter topology to improve voltage regulation and use semiconductor switches having low blocking voltage capability such as MOSFETs. This inverter can be operated with two modes, Full Power Mode (FPM) and Half Power Mode (HPM). In FPM inverter supplies the high frequency step up transformer with full DC-link voltage and in HPM with half DC-link voltage. HPM switching method will be adopted when CCPS output voltage reaches the preset target value and operates in refresh mode-charge is maintained on the capacitor. In this topology each semiconductor devices blocks a half of the DC-link voltage[2]. A 15kW, 30kV CCPS has been built and will be tested for an electric precipitator application. The CCPS operates from an input voltage of 500VDC and has a variable output voltage between 10 to 30kV and 1kHz repetition rate at 44nF capacitive load [3]. A resonant frequency of 67.9kHz was selected and a voltage regulation of $0.83\%$ has been achieved through the use of half power mode without using the forced cut off the switch current [1]. The theory of operation, circuit topology and test results are given.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.386-392
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• 1991

If we rely only on the conventional technology, It may be difficult to meet the recent requirments to electric power system such as further improvement of the quality of electric power supply, technology problems environmental compatibility and so on. Nowadays, power engineers much interest in applying new technology to power system industry. It is confirmed the technology of superconductivity applied components plays an important role in solving the problems of power system, because superconductors, used in suitable applications, can make electric power equipment smaller, lighter, more efficient and perhaps with better dynamic response. Two specific applications are considered here : electric machinery (Generators, Superconducting Magnetic Energy Storage, Transformer, Current limitter) and transmission line. The paper addresses the limitation of conventional technology, the technology impact & problems of superconductivity applied components to future power system from qualitative and some quantitative viewponts. The paper close with questions posed to simulate thinking on how superonductivity might be applied to power systems on a holistic basis.

• Proceedings of the KIPE Conference
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• 2001.12a
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• pp.139-143
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• 2001

Recently, the interest on power quality has been hot issue. The equipments cause voltage disturbance and has become more sensitive to the voltage disturbance. This paper deals with 5-Level H-Bridge Line-Inter active Dynamic Voltage Restorer(LIDVR) system. The LIDVR has following advantages in comparison with the DVR with series injection transformer It has the power factor near to unity under normal source voltage, can compensate the harmonic current of the load and the instant interruption, and has the fast response. First, the construction, the operation mode and algebraic modeling of LIDVR are reviewed. And then a voltage controller is proposed to get sinusoidal load voltage with constant amplitude. To find PWM method suitable for H-Bridge converter, two PWM methods are compared and analyzed. Finally, simulation results verify the proposed 5-level H-Bridge LIDVR system.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.6
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• pp.515-522
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• 2013

In this paper, a new PCS is proposed which is consisted of high boost dual converter and single phase half-bridge inverter. The proposed PCS is configured in parallel input / serial output, using two interleaved voltage doubler converter. Converter of the proposed PCS is distribute input current by configuring parallel input and reduced turn ratio of transformer by configuring serial output. Also, compositions of the inverter are composed of serial output capacitor of converter and half-bridge inverter. The dual converter and single phase half-bridge inverter is designed and characteristic of the new PCS is analysed. The system of the 1.5[kW] PCS is verified through an experimental about operation and stability.