Duk-You Kim

Wide-Range ZVS Phase-Shift Full-Bridge Converter With Reduced Conduction Loss Caused by Circulating Current

A conventional phase-shift full-bridge (PSFB) converter with two clamp diodes and an additional resonant inductor is widely used for front-end dc/dc stage in the distributed power system. However, the hold-up-time requirement limits its operating duty ratio at normal operation. It results in conduction loss caused by circulating current. Therefore, a wide-range zero-voltage switching (ZVS) PSFB converter with reduced conduction loss caused by circulating current is proposed in this paper. The proposed converter adopts the large resonant inductance and replaces clamp diodes in the conventional PSFB converter with MOSFET switches. With these modifications, the proposed converter can achieve the ZVS operation over wide load range as well as can reduce the conduction loss caused by the circulating current. These advantages result in the improvement of whole load efficiency. The operational principle and analysis of the proposed converter are presented and verified by the 1.2-kW prototype.

Synthesis of Li2TiO3 ceramic breeder powders by the combustion process

Abstract The synthesis of the ultra-fine Li 2 TiO 3 powder by the combustion reaction of lithium nitrate, titanium nitrate and specific fuels was investigated. Ultrafine Li 2 TiO 3 powders could be synthesized using glycine or a mixture of urea and citric acid. A pure Li 2 TiO 3 phase was obtained by the simple process without further calcination reaction. The specific surface area of the as-synthesized powder was 10 to 14 m 2 /g and the primary particle size was about 30 nm. The Li 2 TiO 3 body sintered at 800°C for 3 h had dense agglomerates which were formed by the inter-agglomerate sintering process. Each of the agglomerates consisted of very fine grains with a size of 0.3 to 0.5 μm.

A Simple Switching Control Technique for Improving Light Load Efficiency in a Phase-Shifted Full-Bridge Converter with a Server Power System

In phase-shifted full-bridge (PSFB) converter, using discontinuous conduction mode (DCM) is one of the most effective ways to improve efficiency in the light load condition. DCM of the PSFB converter allows getting reduced the duty ratio and zero voltage switching (ZVS) in the light load condition. Because of its simplicity, commercial IC adapted DCM by turning-off synchronous rectifiers (SRs). However, turning-off SRs causes large conduction losses in body diodes of SRs, and ZVS condition or optimized dead time are not defined yet. This letter proposes to use “AND-gated” control signals for SRs to reduce conduction losses in body diodes. Also, the ZVS condition is presented to design dead time easily. The feasibility of the proposed technique has been verified with 90-265 Vac input, 400 V link voltage, and 12V/750 W output server computer power supply system.

A Three-Level Converter With Reduced Filter Size Using Two Transformers and Flying Capacitors

This paper proposes a pulse-width modulation (PWM) three-level converter with reduced filter size using two transformers. The proposed converter has many advantages. All switches sustain only the half of the input voltage and since the secondary rectified voltage is a three-level waveform, the output filter inductor can be reduced. Also, because of the power sharing of transformer and reduced output inductor, high efficiency can be obtained. The operational principle, analysis, and design considerations of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results from a prototype with 600W, 500–600V input, and 60V output.

High-Efficiency Slim Adapter With Low-Profile Transformer Structure

This paper presents the implementation of a high-efficiency slim adapter using an resonant converter. A new structure of the slim-type transformer is proposed, which is composed of copper wire as the primary winding and printed-circuit-board winding on the outer layer as the secondary winding. The proposed structure is suitable for a slim and high-efficiency converter because it has advantages of easy utilization and wide conductive cross-sectional area. In addition, the voltage-doubler rectifier is applied to the secondary side due to its simple structure of secondary winding, and a filter is adopted to reduce the output filter size. The validity of this study is confirmed by the experimental results from an 85-W prototype.

Variable Delay Time Method in the Phase-Shifted Full-Bridge Converter for Reduced Power Consumption Under Light Load Conditions

This paper proposes a new control method in the phase-shifted full-bridge converter for the server power supply, which is variable delay time of lagging-leg switches under the light load conditions. By widening the delay time, the switching occurs at the lower drain–source voltage and then switching loss can be reduced under the light load conditions. The voltage stress of synchronous rectifier switches is also reduced. Without additional power devices and side effects at heavy load condition, the higher efficiency under the light load conditions can be obtained. The analysis and experimental results are presented in this paper to confirm the validity of this study.

Wide range ZVS phase shift full bridge converter with low conduction loss

The conventional phase shift full bridge (PSFB) converter is widely used for front-end DC/DC stage of distributed power system (DPS). However, hold-up time requirement limits its operating duty ratio in normal operation and it results in the increase of conduction loss in conventional PSFB converter. Therefore, wide range ZVS PSFB converter with low conduction loss is proposed in this paper. The proposed converter adopts the large resonant inductor and replaces clamp diodes in conventional PSFB converter with MOSFET switches. With this modification, the proposed converter can achieve the ZVS operation over wide load range as well as can reduce the conduction loss of switches caused by the circulating current. There advantages result in the improvement of whole load efficiency. The operational principle and analysis of proposed converter are presented and verified by the 1.2kW prototype.

Magnetic resonant wireless power transfer for propulsion of implantable micro-robot

Recently, various types of mobile micro-robots have been proposed for medical and industrial applications. Especially in medical applications, a motor system for propulsion cannot easily be used in a micro-robot due to their small size. Therefore, micro-robots are usually actuated by controlling the magnitude and direction of an external magnetic field. However, for micro-robots, these methods in general are only applicable for moving and drilling operations, but not for the undertaking of various missions. In this paper, we propose a new micro-robot concept, which uses wireless power transfer to deliver the propulsion force and electric power simultaneously. The mechanism of Lorentz force generation and the coil design methodologies are explained, and validation of the proposed propulsion system for a micro-robot is discussed thorough a simulation and with actual measurements with up-scaled test vehicles.

Switched capacitor with chain structure for cell-balancing of lithium-ion batteries

In rechargeable batteries such as lithium-ion, the cell balancing circuit is necessary to enhance life time and guarantee safety. Switched capacitor circuit is a cost-effective and simple cell balancing method, but it shows the prolonged balancing time caused by a cell-to-cell energy shift. Therefore, this paper proposes switched capacitor with chain structure to increase balancing speed. In this paper, balancing principle of conventional switched capacitor is explained and the mechanism of charge transfer between adjacent cell and faraway cell is analyzed. Two proposed circuits with the chain structure are described. From the chain structure, the uppermost cell can be adjacent cell of the undermost cell by using additional switches and capacitor, and it can achieve faster cell balancing. Balancing performances of the proposed circuits are confirmed with PSIM simulation, and comparisons between conventional and the proposed circuits are presented. Experimental results are also shown to verify the validity of the proposed structures.

Adaptive link capacitor voltage control for server power system

An adaptive link capacitor voltage variation control method for server power supply is proposed. In this paper, to increase the efficiency under light load condition, the proposed scheme adjusts nominal link capacitor voltage with the consideration of the hold-up time requirement. Thereby, the effective duty ratio of DC/DC stage can be expanded and we can save the power loss. Therefore, power losses on the major components of both PFC stage and DC/DC stage can be decreased when the proposed scheme is applied. The analysis and design considerations are presented. To confirm the validity of the proposed control scheme, experimental results from the 1200W prototype power supply are presented.