216 Journal of Electrical Engineering & Technology, Vol. 1, No. 2, pp. 216~225, 2006 A Novel type of High-Frequency Transformer Linked Soft-Switching PWM DC-DC Power Converter for Large Current Applications Keiki Morimoto*, Nabil A. Ahmed † , Hyun Woo Lee** and Mutsuo Nakaoka** Abstract – This paper presents a new circuit topology of DC busline switch and snubbing capacitor- assisted full-bridge soft-switching PWM inverter type DC-DC power converter with a high frequency link for low voltage large current applications as DC feeding systems, telecommunication power plants, automotive DC bus converters, plasma generator, electro plating plants, fuel cell interfaced power conditioner and arc welding power supplies. The proposed power converter circuit is based upon a voltage source-fed H type full-bridge high frequency PWM inverter with a high frequency transformer link. The conventional type high frequency inverter circuit is modified by adding a single power semiconductor switching device in series with DC rail and snubbing lossless capacitor in parallel with the inverter bridge legs. All the active power switches in the full-bridge inverter arms and DC busline can achieve ZVS/ZVT turn-off and ZCS turn-on commutation operation. Therefore, the total switching losses at turn-off and turn-on switching transitions of these power semiconductor devices can be reduced even in the high switching frequency bands ranging from 20 kHz to 100 kHz. The switching frequency of this DC-DC power converter using IGBT power modules is selected to be 60 kHz. It is proved experimentally by the power loss analysis that the more the switching frequency increases, the more the proposed DC-DC converter can achieve high performance, lighter in weight, lower power losses and miniaturization in size as compared to the conventional hard switching one. The principle of operation, operation modes, practical and inherent effectiveness of this novel DC-DC power converter topology is proved for a low voltage and large current DC-DC power supplies of arc welder applications in industry. Keywords: DC-DC power converter, High frequency transformer link, Quasi-resonant soft-switching PWM, Active Snubber by DC rail switch and lossless capacitor, Low voltage large current DC power supply, Arc welding power supply 1. Introduction Generally, the high performance isolated DC-DC power conditioning converter type semiconductor switching mode power supplies ranging from several kW to about 30 kW or more have been practically required for DC feeding systems, telecommunication power plants, automotive DC bus converters, plasma generator, electro plating plants as well as promising fuel cell interfaced power conditioner and the power supplies of TIG and MIG arc welding applications in industry. Many downsized arc welding high frequency switching mode high power supplies using power MOSFETs, IGBTs and SITs with the aid of transformer resonant, quasi-resonant and multi-resonant circuit topologies have been begun to be developed for large current applications and partially put into practice. However, high frequency resonant power converter topologies on the basis of series resonant, parallel resonant, series and parallel resonant circuits have been adopted for the low voltage and large current DC switch mode power supplies with DC output power rating not more than 10kW due to the effective cost and difficulty to condition the DC output voltage with high power conversion efficiency. Therefore, high frequency pulse width modulated switching mode DC-DC power converters with a high frequency transformer, which is based upon hard-switching PWM voltage source-fed full-bridge inverter circuit operating in the switching frequency of 10 kHz, have been considered widely for output power supplies designed for low voltage-large current applications as arc TIG/MIG welding machines in industry. Under this technological situation, high performance and high efficiency DC-DC power converter with an isolated transformer link should be practically developed for higher power arc welder more than 10 kW and high switching frequency bands ranging from 20 kHz to 100 kHz or more. † Corresponding Author: Dept. of Electrical and Electronic Engineering, Sophia University, Tokyo, Japan. (nabil@power.ee.sophia.ac.jp) * Welding Engineering Dept, DAIHEN Corporation, Osaka, Japan ** Electric Energy Saving Research Center, Dept. of Electrical and Electronic Engineering, Kyungnam Univerity, Masan, Korea. Received August 10, 2005; Accepted March 18, 2006