• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.82-89
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• 2021

This study proposes a DAB two-stage series structure with insulated bidirectional DC-DC converter for two-way power transfer between the renewable energy of high voltages (1 kV and above). The proposed circuit transforms the existing DAB converter into a two-stage series structure to reduce the pressure in the switch. The problem of power imbalance occurring in the design of the DAB converter second-stage series is improved by applying the cell balancing method circuit and the common mode coupled inductor using an external flying capacitor instead of reflecting the existing improvement measures, voltage balance control, and inductor current control. In addition, a no-load supercharging sequence is proposed in high voltages and high-speed switching by using the fixed duty output method. This study presents the analysis results through the structure of the proposed circuit, the principle of improving the power imbalance problem, and simulations. Prototypes were manufactured to meet the specifications of input/output voltage of 1700 V, maximum load of 65 kW, and switching frequency of 51kHz, and the validity of the topology was verified using the experimental results and efficiency data.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.6
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• pp.66-73
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• 2002

This paper presents ZVZCS(Zero-Voltage and Zero-Current Switching) Three Level DC/DC Converter without primary freewheeling diodes. The new converter presented in this paper used a phase shirt control with a flying capacitor in the primary side to achieve ZVS for the outer switches. A secondary anxiliary circuit which consists of one small capacitor, two small diodes and one coupled inductor, is added in the secondary to provide ZVZCS conditions to primary switches, ZVS for outer switches and ZCS for inner switches. Many advantages include simple secondary auxiliary circuit topology, high efficiency, and low cost make the new converter attractive for high power applications. Also the circulating current flows through the circuit so that it causes the needless coduction loss to be occurred in the devices and the transformer of the circuit The new converter has no primary auxiliary diodes for freewheeling current. The principle of operation, feature and design considerations are illustrated and verified through the experiment with a 1[㎾］ 50[KHz］IGBT based experimental circuit.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.5
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• pp.397-400
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• 2018

This paper presents a miniaturized 65 nm CMOS 30~46 GHz wideband amplifier. To minimize the chip area, coupled inductors are used in the matching networks. The measurement shows that the fabricated amplifier exhibits 9.3 dB of peak gain, 16 GHz of 3 dB bandwidth, and 42 % fractional bandwidth. The measured input and output return losses were more than 10 dB at 35.8~46.0 GHz and 28.6~37.8 GHz, respectively. The chip consumes 42 mW at 1.2 V. The measured group delay variation is 19.1 ps within the 3 dB bandwidth and the chip size excluding the pads is $0.09mm^2$.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.5
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• pp.373-380
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• 2016

In this paper, a 50-kW high-efficiency modular fast charger for both electric vehicle (EV) and neighborhood electric vehicle (NEV) is proposed. The proposed fast charger consists of five 10-kW modules to achieve fault tolerance, ease of thermal management, and reduce component stress. Three-level topologies for both AC-DC and DC-DC converters are employed to use 600V MOSFET, resulting in ease of component selection and increase in switching frequency. The proposed three-level DC-DC converter with coupled inductor and its hybrid switching method can reduce the circulating current under wide output voltage range. A 50-kW prototype of the proposed fast charger was developed and tested to verify the validity of the proposed concept. Experimental results show that the proposed fast charger achieves a rated efficiency of 95.2% and a THD of less than 3%.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.3
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• pp.267-274
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• 2016

In this study, a fast charger for electric vehicle with wide charging voltage range is proposed. To achieve high efficiency, three-level topologies are employed for the AC-DC and DC-DC converters. Given that the output range of the DC-DC converter in fast chargers is quite wide, the circulating current of conventional three-level converter will increase under low voltage condition. The proposed hybrid switching method mitigates this issue. When a coupled inductor is used on the output side, the circulating current is further reduced, and the switches $S_2$, $S_3$, $S_6$, and $S_7$ achieve turning-off under the ZCS condition. Experimental results from a 50 kW prototype are provided to validate the proposed charger, and a rated efficiency of 95.9% is obtained.

• Journal of Power Electronics
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• v.9 no.2
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• pp.164-172
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• 2009

Recently, 2-dimensional flat light sources have been attracting much attention for its use in LCD backlight applications because of its high luminous efficiency and uniformity. A long-gap discharge, mercury-tree flat fluorescent lamp has been developed, which shows a high brightness ($>5000\;cd/m^2$) and high luminous efficacy (60 lm/W). Additionally, it has a wide operating margin and stable driving condition with the aid of an auxiliary electrode. For driving the lamp, a narrow pulse power to maintain the glow discharge state is required. Since there has been no research for this kind of lamp driving, this paper proposes a newly developed short-pulse, high-voltage lamp-driving scheme. The proposed lamp system uses a ballast with a coupled-inductor in order to raise the short pulse voltage up to the lamp ignition level and to obtain energy-recovery action during the glow discharge mode. The operation principles are presented and also the system performances such as the lighting efficiency, spatial and angular uniformities are evaluated by hardware experiments. The results show that the proposed lighting system is a good candidate for the next-generation of LCD backlight systems.

• Journal of Power Electronics
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• v.13 no.4
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• pp.592-599
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• 2013

This paper investigates a new isolated single-phase AC-DC converter, which integrates a modified AC-DC buck-boost converter with a DC-DC forward converter. The front semi-stage is operated in discontinuous conduction mode (DCM) to achieve an almost unity power factor and a low total harmonic distortion of the input current. The rear semi-stage is used for step-down voltage conversion and electrical isolation. The front semi-stage uses a coupled inductor with the same winding-turn in the primary and secondary sides, which is charged in series during the switch-on period and is discharged in parallel during the switch-off period. The discharging time can be shortened. In other words, the duty ratio can be extended. This semi-stage can be operated in a larger duty-ratio range than the conventional AC-DC buck-boost converter for DCM operation. Therefore, the proposed converter is suitable for universal input voltage (90~264 $V_{rms}$) and a wide output-power range. Moreover, the voltage stress on the DC-link capacitor is low. Finally, a prototype circuit is implemented to verify the performance of the proposed converter.

• Journal of Power Electronics
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• v.17 no.5
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• pp.1137-1149
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• 2017

In order to reduce the cost, improve the efficiency and simplify the complicated control of existing isolated LED drivers, an improved boundary conduction mode (BCM) Buck ac-dc light emitting diode (LED) driver with extended output voltage and low total harmonic distortion is proposed. With a coupled inductor winding and a stacked output, its output voltage can be elevated to a much higher value when compared to that of the conventional Buck ac-dc converter, without sacrificing the input harmonics and power factor. Therefore, the proposed Buck LED driver can meet the IEC61000-3-2 (Class C) limitation and has a low THD. The operating principle of the topology and the design methodology of the ac-dc LED driver are presented. A 150 W ac-dc prototype was built in the laboratory and it shows that the input current harmonics meet the lighting standard. In addition, the THD is less than 16% at a typical ac input. The peak efficiency is higher than 96.5% at a full load and a normal input.

• Journal of Power Electronics
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• v.14 no.5
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• pp.815-826
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• 2014

An improved bridgeless interleaved boost power factor correction (PFC) rectifier to improve power efficiency and component utilization is proposed in this study. With combined conventional bridgeless PFC circuit and interleaved technology, the proposed rectifier consists of two interleaved and magnetic inter-coupling boost bridgeless converter cells. Each cell operates alternatively in the critical conduction mode, which can achieve the soft-switching characteristics of the switches and increase power capacity. Auxiliary blocking diodes are employed to eliminate undesired circulating loops and reduce current-sensing noise, which are among the serious drawbacks of a dual-boost PFC rectifier. Magnetic component utilization is improved by symmetrically coupling two inductors on a unique core, which can achieve independence from each other based on the auxiliary diodes. Through the interleaved approach, each switch can operate in the whole line cycle. A simple control scheme is employed in the circuit by using a conventional interleaved controller. The operation principle and theoretical analysis of the converter are presented. A 600 W experimental prototype is built to verify the theoretical analysis and feasibility of the proposed rectifier. System efficiency reaches 97.3% with low total harmonic distortion at full load.

• Proceedings of the KIPE Conference
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• 2019.11a
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• pp.19-21
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• 2019

본 논문에서는 용접 전문의 전력단 스위치로 MOSEFT을 사용하는 ZVS-PWM 스위칭 방식의 풀브리지 회로에 대한 연구결과를 발표한다. 제안된 ZVS-PWM 풀브리지 컨버터는 스위칭 주파수를 60kHz로 사용하고 변압기를 병렬로 적용해 고전력밀도를 갖도록 설계되었다. 변압기 병렬 구동 시 발생하는 전력 불균형 현상은 공통모드 결합 인덕터(CMCI; Common Mode Coupled Inductor) 부착을 통해 개선되었다. 본 논문은 제안된 회로의 연구를 실험을 통해 검증하고 이에 대한 실험 결과 및 분석을 나타내고 있다.