• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.2
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• pp.104-111
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• 1997

In this paper, three-phase PWM AC to DC boost converter that operates with unity power factor and sinusodial input line currents is presented. The current control of this converter is based on the space vector PWM strategy with fixed switching frequency and the line currents track to reference currents within one sampling time interval. By using this control strategy low ripples in the outut current and the voltage as well as fast dynamic response are achieved with small dc link cpacitance employed.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.188-190
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• 1995

This paper describes a soft switching using discontinuous inductor current. The soft switching snubber circuit provides ZCS and ZVS for main switch. For high power applications, the input ractifier is fed from a three-phase ac source. The Conventional switching method is hard switching technics, because of the device turn off is ocurred in maximum reactor current. In this time, switching losses are maximised by the hard switching. In generally, soft switching technique has been adjusted with the snubber condenser in order to compensates for this losses. So, it was compared hard switching with soft switching which has proposed in this paper for switching losses, distortion factor by the simulation.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1207-1208
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• 2006

Recently, a fuel cell with low voltage and high current output characteristics is remarkable for new generation system. It needs both a DC-DC step-up converter and DC-AC inverter to be used in fuel cell generation system. Therefor, this paper, consists of an isolated DC-DC converter to boost the fuel cell voltage 380[VDC] and a PWM inverter with LC filter to convent the DC voltage to single-phase 220[VAC]. Expressly, a tapped inductor filter with freewheeling diode is newly implemented in the output filter of the proposed high frequency isolated ZVZCS PWM DC-DC converter to suppress circulating current under the wide output voltage regulation range, thus to eliminate the switching and transformer turn-on/off over-short voltage or transient phenomena. Besides the efficiency of 93-97[%] is obtained over the wide output voltage regulation ranges and load variations.

• 전기의세계
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• v.23 no.4
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• pp.60-65
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• 1974

This paper is to study on the pilot work of bi-directional S.C.R. power converter adopted by the method of diode-bridge type circuit. This apparatus acts as a converter when it is used in convering 3-phase a.c source to d.c output, and it can be used as an inverter which recovering surplus d.c power to a.c source when d.c load become active to cause the induced voltage higher than the presetted point of d.c output voltage. At the same time, its d.c voltage varies continuously in the presetted range of positive and/or negative polarity. As a result of test, the AC/DC bi-directional power converter represents maximum converting efficiency of 91% and power factor of 0.98. Furthermore, this converter also can be applied as a cycleconverter by varying the period of gate triggering signal.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.367-370
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• 1987

A high-performance PWM technique in current-controlled AC to DC converter is introduced. This converter used information about source voltage vectors to make good PWM switching pattern that it can control the DC output voltage with reduced ripple factor and rapid response. In addition to reduction of harmonic current, AC input power factor can be controlled to leading or lagging by current reference. Simulation was made based on analytical approach and it showed a good agreement with theory.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.14-15
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• 2013

본 논문에서는 컨버터의 병렬운전을 하는데 있어 제안한 드룹제어를 사용하여 전력을 분담한다. 제안한 방법을 이용하면 직류배전에서 병렬시스템의 용량증설을 용이하게 할 수 있다. 기존의 교류전원에서 사용하는 드룹 제어 방법을 새롭게 개선하여 직류전원에서 드룹 제어가 적용되도록 드룹 제어기를 설계한다. 그리고 제안한 드룹 제어기의 제어방법을 상세히 설명한다. 본 논문에서는 제안한 제어방법을 50[kW] 직류배전 시스템에 적용하여 시뮬레이션을 통하여 제안된 기법의 타당성을 검증한다.

• Progress in Superconductivity and Cryogenics
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• v.6 no.2
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• pp.25-28
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• 2004

Three-phase inductive superconducting fault current limiter (SFCL) with DC reactor rated on 6.6 $KV_{rms}/200 A_{rms}$ has been developed in Korea. This system consists of one DC reactor, AC/DC power converter, and a three-phase transformer, which is called magnetic core reactor (MCR). This paper deals with the short-circuit analysis of the SFCL. The DC reactor was the HTS solenoid coil whose inductance was 84mH. The power converter was performed as the dual-mode operation for dividing voltage between the rectifying devices. The short-term normal operation (1 see) and short-circuit tests (2∼3 cycles) of this SFCL were performed successfully. In regular short-circuit test, the fault current was limited as 30% of rated short-circuit current at 2 cycles after the fault. The experimental results have a very similar tendency to the simulation results. Using the technique for the fault detection and SCR firing control, the fault current limiting rate of the SFCL was improved. From this research, the parameters for design and manufacture of large-scale SFCL were obtained.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.4
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• pp.57-66
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• 2012

When typical Z-source DC/AC inverter(ZSI) is operated in high voltage gain area, because of its high duty ratio, voltage and current stress in Z-network of typical ZSI are increased. This paper proposes a new switched trans ZSI(STZSI) with two switched trans cells which consist of one trans and two diodes. To confirm the operation performance of the proposed system, the PSIM simulation is performed for typical ZSI, switched inductor ZSI and the proposed STZSI. Voltage / current stress and transient state characteristics of each method are compared under the condition of DC input voltage 100[V] and output phase voltage 66[Vrms]. As a result, we confirmed that transient state of the proposed STZSI is short compared with the conventional ZSI because the high voltage gain is obtained using the same duty ratio, also a low duty ratio is required for the same output voltage. Finally, we could know the proposed system have low voltage and current stress in Z-network compared with the conventional ZSI.

• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.77-81
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• 2004

In this paper a novel line interactive UPS (Uninterruptible Power Supply) using the two 4-leg VSCs and AC line reactor is proposed. The 4-leg Voltage Source Converter(VSC) can use the DC link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by $15\%$ in comparison to that of the conventional line-interactive UPS system. One VSC is in parallel with the AC line reactor of the power source side, and the other is in series with the load. The parallel 4-leg voltage source inverter controls three-phase line voltage independently in order to control the line reactor current indirectly. It eliminates the neutral line current and the active ripple power of the source side using the pqr theory so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series 4-leg voltage source inverter compensates the line voltage and allows the load voltage to be balanced and harmonic-free. Both of parallel and series 4-leg voltage source inverters always act as independently controllable voltage sources, so that three-phase output voltage shows a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through computer simulation results.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.568-572
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• 1994

This paper presents equipment for charging and discharging with high power factor aid high efficiency. This equipment is consisted of $3{\phi}$SPWM AC/DC converter for improving input current waveform and input power factor, and bidirectional DC/DC converter for electric isolation in the DC link Part. Therefore, Input power factor and the total efficiency in the proposed system can be increased more than in the conventional phase-controlled thyristor Charging - Discharging System.