Woo-Young Choi

Bio: Woo-Young Choi is an academic researcher from Pohang University of Science and Technology. The author has contributed to research in topics: Power factor & Boost converter. The author has an hindex of 15, co-authored 26 publications receiving 1041 citations. Previous affiliations of Woo-Young Choi include Samsung.

Bridgeless Boost Rectifier With Low Conduction Losses and Reduced Diode Reverse-Recovery Problems

Abstract: A bridgeless boost rectifier with low conduction losses and reduced diode reverse-recovery problems is proposed for power-factor correction. The proposed boost rectifier can reduce the conduction losses and alleviate the diode reverse-recovery problems by using a coupled inductor and two additional diodes. Zero-current turn-off of the output diodes is achieved, and the reverse-recovery currents of the additional diodes are slowed down to reduce the diode reverse-recovery losses. All inductive components are realized on a single magnetic core by utilizing the leakage inductance of the coupled inductor. Furthermore, for the use of this topology in the practical design, the linear peak current mode control is employed for the proposed boost rectifier. A detailed analysis and a control strategy are presented. Experimental results for a 300-W prototype are also discussed to show the performance of the proposed boost rectifier

Single-Stage Single-Switch PFC Flyback Converter Using a Synchronous Rectifier

Abstract: A single-stage single-switch power factor correction (PFC) flyback converter with a synchronous rectifier (SR) is proposed for improving power factor and efficiency. Using a variable switching-frequency controller, this converter is continuously operated with a reduced turn-on switching loss at the boundary of the continuous conduction mode and discontinuous conduction mode (DCM). The proposed PFC circuit provides relatively low dc-link voltage in the universal line voltage, and also complies with Standard IEC 61000-3-2 Class D limits. In addition, a new driving circuit as the voltage driven-synchronous rectifier is proposed to achieve high efficiency. In particular, since a driving signal is generated according to the voltage polarity, the SR driving circuit can easily be used in DCM applications. The proposed PFC circuit and SR driving circuit in the flyback converter with the reduced switching loss are analyzed in detail and optimized for high performance. Experimental results for a 19 V/90 W adapter at the variable switching-frequency of 30~70 kHz were obtained to show the performance of the proposed converter.

Surface Morphology, Molecular Reorientation, and Liquid Crystal Alignment Properties of Rubbed Nanofilms of a Well-Defined Brush Polyimide with a Fully Rodlike Backbone

Abstract: Nanoscaled films of poly{p-phenylene 3,6-bis[4-(n-butoxy)phenyloxy]pyromellitimide} (C4-PMDA-PDA PI), a well-defined brush polyimide (PI) composed of aromatic−aliphatic bristles set into a fully rodlike polymer backbone (two bristles per chemical repeat unit of the polymer backbone), were studied by atomic force microscopy, optical retardation, prism coupling, and linearly polarized IR spectroscopy before and after mechanical rubbing with velvet fabric, and their liquid crystal (LC) aligning abilities were investigated. Uniform, homogeneous LC alignment was achieved at the rubbed film surfaces of PIs with positively birefringent characteristics. Surprisingly, however, the LC alignment director for this PI is perpendicular to the rubbing direction as well as to the reorientation direction of the polymer main chains. This is the first time that LCs on a PI surface have been induced to align in the direction perpendicular to the rubbing direction, a significant departure from the LC alignment observed for al...

Photoreactions and Photoinduced Molecular Orientations of Films of a Photoreactive Polyimide and Their Alignment of Liquid Crystals

Abstract: A soluble photoreactive polyimide (PSPI) with side-group cinnamate (CI) chromophores that forms good quality films through conventional solution spin-casting and drying processes was successfully synthesized with a reasonably high molecular weight: poly(3,3‘-bis(cinnamoyloxy)-4,4‘-biphenylene hexafluoroisopropylidenediphthalimide) (6F-HAB-CI). This 6F-HAB-CI PSPI is thermally stable up to 340 °C, its glass transition temperature (Tg) is 181 °C, and it was determined by prism coupling to be positively birefringent. The photochemical reactions of the PSPI in solution and in films, as well as the molecular orientations of the PSPI that are induced by exposure of its films to linearly polarized ultraviolet light (LPUVL), were investigated in detail by nuclear magnetic resonance, ultraviolet−visible, infrared, and Raman spectroscopies and by dissolution testing and optical retardation measurements. It was confirmed that the CI chromophores of the PSPI undergo both photoisomerization and photodimerization. LPU...

Single-Switch Quasi-Resonant Converter

Abstract: A single-switch quasi-resonant converter is proposed to obtain high efficiency. Using a variable switching frequency control, this converter is continuously operated at the critical conduction mode for soft switching of the power semiconductor switch. By the resonance, the proposed converter reduces the turn-on loss of the switch without additional active switches and alleviates the reverse-recovery losses of the rectifying diodes. Furthermore, the voltage stress of the rectifying diodes due to the output series resonant circuit is clamped to the output voltage. Experimental results for the 48-V/160-W converter at the variable switching frequency are obtained to show the performance of the proposed converter.

Performance Evaluation of Bridgeless PFC Boost Rectifiers

Abstract: In this paper, a systematic review of bridgeless power factor correction (PFC) boost rectifiers, also called dual boost PFC rectifiers, is presented. Performance comparison between the conventional PFC boost rectifier and a representative member of the bridgeless PFC boost rectifier family is performed. Loss analysis and experimental efficiency evaluation for both CCM and DCM/CCM boundary operations are provided.

Performance Evaluation of Bridgeless PFC Boost Rectifiers

Abstract: In this paper, a systematic review of bridgeless PFC boost rectifiers, also called dual boost PFC rectifiers, is presented. Performance comparison between the conventional PFC boost rectifier and a representative member of the bridgeless PFC boost rectifier family is performed. Design considerations and experimental results in both CCM and DCM/CCM boundary operations are provided.

Comprehensive Study of Single-Phase AC-DC Power Factor Corrected Converters With High-Frequency Isolation

Abstract: Solid-state switch mode AC-DC converters having high-frequency transformer isolation are developed in buck, boost, and buck-boost configurations with improved power quality in terms of reduced total harmonic distortion (THD) of input current, power-factor correction (PFC) at AC mains and precisely regulated and isolated DC output voltage feeding to loads from few Watts to several kW. This paper presents a comprehensive study on state of art of power factor corrected single-phase AC-DC converters configurations, control strategies, selection of components and design considerations, performance evaluation, power quality considerations, selection criteria and potential applications, latest trends, and future developments. Simulation results as well as comparative performance are presented and discussed for most of the proposed topologies.

A High-Performance Single-Phase Bridgeless Interleaved PFC Converter for Plug-in Hybrid Electric Vehicle Battery Chargers

Abstract: In this paper, a new front end ac-dc bridgeless interleaved power factor correction topology is proposed for level II plug-in hybrid electric vehicle (PHEV) battery charging. The topology can achieve high efficiency, which is critical for minimizing the charger size, PHEV charging time and the amount and cost of electricity drawn from the utility. In addition, a detailed analytical model for this topology is presented, enabling the calculation of the converter power losses and efficiency. Experimental and simulation results are included for a prototype boost converter converting universal ac input voltage (85-265 V) to 400 V dc output at up to 3.4 kW load. The experimental results demonstrate a power factor greater than 0.99 from 750 W to 3.4 kW, THD less than 5% from half load to full load and a peak efficiency of 98.9% at 70 kHz switching frequency, 265 V input and 1.2 kW load.

Operation Mode Analysis and Peak Gain Approximation of the LLC Resonant Converter

Abstract: With the advantage of achieving zero voltage switching for a wide input voltage range, the LLC resonant topology has become increasingly popular for use in high power density and high-efficiency power converter applications. However, when the LLC converter is applied to wide input voltage range applications, the widely used fundamental harmonic approximation is incapable of guiding the design due to its inaccuracy. Thus an accurate LLC converter model is desired. In this paper, a generalized mode analysis is presented that provides highly accurate prediction on resonant current and voltage behavior and dc gain characteristic. Also, because operation modes are affected by load, frequency, and gain conditions, the boundaries and distribution of modes are discussed and illustrated. Based on the mode analysis, an approximation method is developed to estimate the peak gain point, which is useful in LLC design. This approximation demonstrates high accuracy within the simulation results. An experimental prototype is built to verify the analysis.