• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.1
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• pp.72-81
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• 2009

This paper presents quasi-resonant type high power factor ac power supply for atmospheric pressure plasma cleaning system adopting three phase PFC boost converter and it's control method. The presented ac power supply consists of single phase H-bridge inverter, step-up transformer for generating high voltage and three phase PFC boost converter for high power factor on source utility. Unlikely to the traditional LC resonant converter, the propose one has an inductor inside only. A single resonant takes place through the inside inductor and the capacitor from the plasma load modeled into two series capacitor and one resistance. The quasi-resonant can be achieved by cutting the switching signal when the load current decrease to zero. To obtain power control ability, the propose converter controlled by two control schemes. One is the changing output pulse period scheme in the manner of PFM(Pulse Frequency Modulation) control. On the other, to provide more higher power to load, the DC rail voltage is directly controlled by the 3-phase PFC boost converter. The significant merits of the proposed converter are the uniform power providing capability for high quality plasma generation and low reactive power in AC and DC side. The proposed work is verified through digital simulation and experimental implementation.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.3
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• pp.209-218
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• 2011

In low voltage high current applications such as fuel cells the current-fed DC-DC converter which has small ripple current and turn ratio is more efficient. In the applications larger than 5kW the conventional single-phase current-fed converter based on full-bridge, half-bridge or push-pull topologies has high current burden of devices such as switches, and the selection and optimized design of the devices are not easy. In this paper a three-phase active-clamped current-fed push-pull DC-DC converter suitable for high power high step-up applications is proposed. The proposed converter has reduced current burden and is suitable for wide input voltage applications due to the use of whole duty cycle range. Design methods of main components including three-phase high frequency transformers are provided, and the validity and performance of the proposed converter are proved from a 5kW prototype.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2701-2703
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• 1999

A new mode of parallel operation of a modular 3-phase AC-DC Flyback converter for high power factor correction along with tight regulation is presented in this thesis. The converter offers input/output transformer isolation for safety, a unity input power factor for minimum reactive power, high efficiency and high power density for minimum weight and volume. Compared with previously developed 3-phase two-stage power converter, the advantage of the proposed converter does not require expensive high voltage and high current devices that are normally needed in popular boost type 3-phase converter. In this paper, a detailed small signal analysis of the modular 3-phase AC-DC flyback converter is provided for control purposes and also experimental results are included to confirm the validity of the analysis.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.5
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• pp.372-375
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• 2021

A three-leg inverter-type isolated DC-DC Converter that can use 220 and 440 V grid input voltages is introduced. The secondary circuit structure of the proposed topology is center-tap, which is the same as the conventional phase-shifted full-bridge converter. However, the primary circuit structure is composed of a three-leg inverter structure and a transformer, in which two primary windings are connected in series. The proposed circuit structure has a wider input voltage range than the conventional phase-shifted full-bridge converter, and the circulating-current on the primary-side is reduced. In addition, the voltage stress at the secondary rectifier is greatly improved, and high efficiency can be achieved at a high input voltage by removing the snubber circuit added to the conventional converter. Prototype converters with input DC of 311 V, output of 622 V, and 50 V and 6 kW class specifications were designed and manufactured to verify the validity of the proposed topology; the experimental results are presented.

• Journal of the Korean Society for Railway
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• v.19 no.5
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• pp.617-628
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• 2016

This paper proposes the structure of a smart transformer to improve the performance of the 60Hz main power transformer for rolling stock. The proposed smart transformer is a kind of solid state transformer that consists of semiconductor switching devices and high frequency transformers. This smart transformer would have smaller size than the conventional 60Hz main transformer for rolling stock, making it possible to operate AC electrified track efficiently by power factor control. The proposed structure employs a cascade H-Bridge converter to interface with the high voltage AC single phase grid as the rectifier part. Each H-Bridge converter in the rectifier part is connected by a Dual-Active-Bridge (DAB) converter to generate an isolated low voltage DC output source of the system. Because the AC voltage in the train system is a kind of medium voltage, the number of the modules would be several tens. To control the entire smart transformer, the inner DC voltage of the modules, the AC input current, and the output DC voltage must be controlled instantaneously. In this paper, a control algorithm to operate the proposed structure is suggested and confirmed through computer simulation.

• Journal of Electrical Engineering and Technology
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• v.11 no.1
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• pp.257-264
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• 2016

In this paper, new electric railway feeding system which has active transformer is modeled for evaluating the steady state analysis using PSCAD/EMTDC. Equivalent models including power supply, feeder, train and transformers are proposed for simplifying the model of the feeding system in high speed electric railway. In case study, simulation results applied to proposed model are compared with the conventional and new systems through the catenary voltage, three-phase voltage of PCC (Point of Common Coupling) and the efficiency of regenerative braking energy.

• Progress in Superconductivity and Cryogenics
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• v.5 no.3
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• pp.30-33
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• 2003

1MVA high temperature superconducting (HTS) transformer with double pancake windings made of BSCCO-2223 HTS tapes was designed and manufactured. And prototype transformer with the same capacity was manufactured also. The each rated voltage of the HTS transformer is 22.9 kV and 6.6 kV. Four parallel BSCCO-2223 HTS tapes were wound in the double pancake windings of low voltage side. In order to distribute the currents equally in each HTS tapes, the three times transposition was performed between the double pancake windings. The windings of prototype transformer were wound using copper tape with the same size as BSCCO-2223 HTS tape. The core of the transformer was designed and manufactured as a shell type core made of laminated silicon steel plate. The several characteristics tests for the prototype transformer were performed in liquid nitrogen and insulation tests were accomplished also.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.1873-1877
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• 2010

In the high-speed EMU, the modularized traction converter produces the significant harmonic currents caused from the switching behavior of a power converter. These harmonic currents bring the interference among the traction equipment. One way to minimize the interference is to design the secondary windings of a power transformer decoupled magnetically as possible. This paper presents a magnetic field analysis on a winding disposition to clarify an impact on magnetic decoupling between secondary windings, under a limited height of a train. Two winding dispositions for a single-phase shell-type transformer are constructed and simulated by a three-dimensional finite elements method (FEM) model. Two different winding dispositions are constructed and simulated by three-dimensional FEM model using Maxwell3D.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.12
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• pp.1678-1687
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• 2013

This paper describes a prototype of 3-phase 3.3kV/220V 6kVA modular semiconductor transformer developed in the lab for feasibility study. The developed prototype is composed of three single-phase units coupled in Y-connection. Each single-phase unit with a rating of 1.9kV/127V 2kVA consists of a high-voltage high-frequency resonant AC-DC converter, a low-voltage hybrid-switching DC-DC converter, and a low-voltage hybrid-switching DC-AC converter. Also each single-phase unit has two DSP controllers to control converter operation and to acquire monitoring data. Monitoring system was developed based on LabView by using CAN communication link between the DSP controller and PC. Through various experimental analyses it was verified that the prototype operates with proper performance under normal and sag condition. The system efficiency can be improved by adopting optimal design and replacing the IGBT switch with the SiC MOSFET switch. The developed prototype confirms a possibility to build a commercial high-voltage high-power semiconductor transformer by increasing the number of series-connected converter modules in high-voltage side and improving the performance of switching element.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.438-443
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• 1998

A simple single-stage AC/DC forward converter with transformer magnetic energy feedback technique for power factor correction is proposed. The operational principle of the proposed converter is presented. The proposed converter gives the good power factor correction, low line current harmonic distortions, and tight output voltage regulation. The prototype shows high power factor with low line current harmonics.