Buck Type (8kA, 10V) High Frequency Quasi-Resonant Converter Ilknur Colak ISTANBUL TECHNICAL UNIVERSITY Dep. of Elect. Eng., 34469 Istanbul, Turkey Tel: +90 / (212) – 285.67.45 Fax: +90 / (212) – 285.67.00 ilknur.colak@cern.ch URL: http://www.elk.itu.edu.tr Acknowledgements The author would like to thank TUBITAK-Marmara Research Center Laboratories for hosting this project and for their support to make it possible. In particular, Caner Unsalver, Selim Turan and Erdinc Cekli are also gratefully acknowledged for their valuable support by working day and night for months together in bringing this system out. Keywords «Battery charger», «DC power supply», «Resonant-mode power supply». Abstract Submarine lead-acid batteries need high current, low voltage battery chargers with high DC stability and high dynamic response at low level ripple. A buck type phase shift pulse-width modulated switching quasi-resonant converter is presented in this paper. Switching principles and operation modes of the proposed system are described with design based analysis. The experimental results of a 8kA, 10V modular converter are presented to verify the feasibility of the proposed system. Introduction In low voltage, high current modular applications mostly soft switching techniques are used in the field [1..3]. However, soft switching techniques make the system control more complicated. Recently, quasi-resonant converters have been introduced to replace conventional converters in high power applications. Switching losses are reduced in these converters as zero-current or zero-voltage switching can be realized which increases system efficiency and power density [4..7]. In this study, an application of zero voltage switching in a full bridge converter is introduced which enables high power soft switching. 180° phase shifted gate signals in the same leg are always kept constant but the phase angle between the legs is changed to regulate the output voltage. The phase shifting method has increased the power density of the system by allowing zero voltage transition of the power switches. Experimental results obtained show that the phase shifting pulse width modulation method is a good choice for low voltage, high frequency, and high current applications. They also show that zero voltage transition method reduces the switching losses, and 45° interleaved modules decrease the output ripple. Description of the Proposed Converter This project is designed to test and charge the submarine lead acid batteries. Each battery cell has 12000Ah, 2V dc rated values. The proposed converter should be capable of charging up to four serially connected battery cells with 0.1% and 0.005% voltage and current ripple respectively. Which also means the system has to have very high accuracy for maximum current at minimum output voltage