• Journal of Power Electronics
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• v.3 no.4
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• pp.249-258
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• 2003

This paper presents a high-efficient and cost effective three-phase AC/DC-DC/AC power conversion system with a single two-switch type active Auxiliary Resonant DC Link (ARDCL) snubber circuit, which can minimize the total power dissipation. The active ARDCL snubber circuit is proposed in this paper and its unique features are described. Its operation principle in steady-state is discussed for the three phase AC/DC-DC/AC converter, which is composed of PWM rectifier as power factor correction (PFC) converter, sinewave PWM inverter. In the presented power converter system not only three-phase AC/DC PWM rectifier but also three-phase DC/AC inverter can achieve the stable ZVS commutation for all the power semiconductor devices. It is proved that the proposed three-phase AC/DC-DC/AC converter system is more effective and acceptable than the previous from the cost viewpoint and high efficient consideration. In addition, the proposed two-switch type active auxiliary ARDCL snubber circuit can reduce the peak value of the resonant inductor injection current in order to maximize total system actual efficiency by using the improved DSP based control scheme. Moreover the proposed active auxiliary two-switch ARDCL snubber circuit has the merit so that there is no need to use any sensing devices to detect the voltage and current in the ARDCL sunbber circuit for realizing soft-switching operation. This three-phase AC/DC-DC/AC converter system developed for UPS can achieve the 1.8% higher efficiency and 20dB lower conduction noise than those of the conventional three-phase hard-switching PWM AC/DC-DC/AC converter system. It is proved that actual efficiency of the proposed three-phase AC/DC-DC/AC converter system operating under a condition of soft switching is 88.7% under 10kw output power.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.6
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• pp.356-360
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• 2014

In this paper, the effect of underpass structure on quality factor and breakdown voltage of octagonal inductors which were fabricated with 90 nm complementary metal-oxide-semiconductor (CMOS) technology for radio frequency integrated circuit (RFIC) was studied. It was found that quality factor and breakdown voltage of inductors with more than one metal layer for underpass showed improved properties compared to those with one metal layer. However, little change of quality factor and breakdown voltage was observed between the inductors with two and more than two metal layers for underpass. Therefore, underpasses with two metal layers are promising for RFIC designs of the octagonal inductors in 90 nm CMOS technology.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.3
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• pp.283-288
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• 2005

A portable primary inductance standard set that includes a Maxwell-Wien bridge and a 10 mH standard inductor installed in a thermostat has been developed at KRISS. Two auxiliary resistance capacitance networks (analogous to a 'Wagner ground') provide excellent stability of the bridge balance and impose less strict requirements on the components of these networks. Removable capacitance and ac-dc resistance standards used in the bridge arms made it possible to reproduce 10 mH and 100 mH inductance values in the frequency range of 500 Hz to 3 kHz. From investigations of this standard and preliminary comparison with VNIIM (D. I. Mendeleyev Institute for Metrology), the results have demonstrated that the bridge can be used as a part of the transportable inductance standard with a measurement uncertainty within (1-3) $\mu$H/H at frequencies of 1 kHz and 1.6 kHz. The application of the bridge as a constituent part of the transportable standard gives us an opportunity to eliminate the influence of the standard inductors.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.5
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• pp.396-402
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• 2008

This paper presents the structure and performance of a new Integrated magnetics-based transformer, which can be readily adapted to zero-voltage switching full bridge dc-to-dc converters. The proposed transformer features with two paralleled primary windings and a center-tapped secondary winding. The transformer can be fabricated on standard EE or EI cores where the primary and secondary windings are placed on the outer legs while the output filter inductor is wound on the middle leg. The performance of the proposed transformer is demonstrated with a 100 kHz 720 W experimental dc-to-dc converter which recorded a 92% conversion efficiency at 12 V output voltage.

• Journal of Power Electronics
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• v.15 no.3
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• pp.587-601
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• 2015

A high step-up dc-dc converter is proposed for photovoltaic power systems in this paper. The proposed converter consists of an input current doubler, a symmetrical switched-capacitor doubler and an active-clamp circuit. The input current doubler minimizes the input current ripple. The symmetrical switched-capacitor doubler is composed of two symmetrical quasi-resonant switched-capacitor circuits, which share the leakage inductance of the transformer as a resonant inductor. The rectifier diodes (switched-capacitor circuit) are turned off at the zero current switching (ZCS) condition, so that the reverse-recovery problem of the diodes is removed. In addition, the symmetrical structure results in an output voltage ripple reduction because the voltage ripples of the charge/pump capacitors cancel each other out. Meanwhile, the voltage stress of the rectifier diodes is clamped at half of the output voltage. In addition, the active-clamp circuit clamps the voltage surges of the switches and recycles the energy of the transformer leakage inductance. Furthermore, pulse-width modulation plus phase angle shift (PPAS) is employed to control the output voltage. The operation principle of the converter is analyzed and experimental results obtained from a 400W prototype are presented to validate the performance of the proposed converter.

• 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 Electrical Engineering and Technology
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• v.12 no.2
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• pp.654-664
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• 2017

This paper proposed an unified dual-phase-shift (UDPS) control for dual active bridge (DAB) converters in order to improve efficiency for a wide output power range. Different operating modes of UDPS are characterized with respect to the reactive current distribution. The proposed UDPS has the same output power capability with conventional phase-shift (CPS) method. Furthermore, its implementation is simple since only the change of the leading phase-shift direction is required for different operating power range. The proposed UDPS control can minimize both the inductor rms current and the circulating reactive current for various voltage conversion ratios and load conditions. The optimal phase-shift pairs for two bridges of DAB converter are derived with respect to the comprehensive reactive power loss model, including the reactive components delivered from the load and back to the source. Simulation and experimental results are illustrated and explained with details. The effectiveness of the proposed method is verified in terms of reactive power losses minimization and efficiency improvement.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.556-558
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• 1996

PLS 2-GeV linac has 11 sets of high power klystron-modulator system as a main RF source for the beam acceleration. The modulators can provide 200-MW peak pulsed power(400-kV, 500-A) with a pulse width of $7.5{\mu}s$(ESW), a maximum pulse repetition rate of 120-Hz at the full power level. The DC power supply provides a 25-kV, 7-Adc and the charging system consists of a charging inductor, charging capacitor, and the diode for reverse current protection. The charged PFN voltage by a LC resonant charging method has two times of the DC high voltage and the pulsed power is delivered to the load by a thyratron switch. To reduced the press of high voltage lit thyratron switch, the command charging is the best method. In this article, the high voltage switch for the command charging method is tested to the start work and the system is presented with the experiment results of the trigger and operational characteristics.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.6
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• pp.491-496
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• 2005

In this paper, test on characteristics of 3-phase line-interactive UPS system, known as delta conversion UPS system, is studied. Delta conversion UPS system is new line-interactive UPS system using two series-parallel PWM converters instead of using series inductor in conventional single conversion line-interactive UPS system. It is known that the characteristics of input and output in delta conversion UPS system is much improved by controlling source current of AC lines directly. Here the results on load test, normal/backup mode test, and normal/bypass mode test, which are very important in the test on characteristics of UPS system, is presented. And finally overall evaluation on delta conversion UPS system is given.

• Journal of Power Electronics
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• v.14 no.2
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• pp.203-216
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• 2014

In the conventional dc-dc converter, a pair of additional diode and the adjacent passive component capacitor/inductor can be added to the circuit with an X-shape connection, which generates a family of new topologies. The novel circuits, also called diode-assisted dc-dc converter, enhance the voltage boost/buck capability and have a great potential for high step-up/step-down power conversions. This paper mainly investigates and compares conventional dc-dc converter and diode-assisted dc-dc converter in wide range power conversion from the aspects of silicon devices, passive components requirements, electro-magnetic interference (EMI) and efficiency. Then, a comprehensive comparison example of a high step-up power conversion system was carried out. The two kinds of boost dc-dc converters operate under the same operation conditions. Mathematical analysis and experiment results verify that diode-assisted dc-dc converters are very promising for simultaneous high efficiency and high step-up/step-down power conversion in distributed power supply systems.