Abstract

Full bridge dc/de converter topology is extensively applied in medium to high power conversion. In a power level up to 3 kW, the full bridge converter now employs MOSFET switches. High efficiency, high power density, high reliability and low EMI are some of the most desirable features in these applications, particularly for computer and telecom systems. To achieve these features, soft switching techniques are normally employed. However, the conventional soft switching full bridge converter topologies would either lose the soft switching at some operating conditions, or become rather complex in design and implementation for a few kilo watts applications. This thesis presents and analyzes an improved zero voltage switching dc/dc full bridge converter topology. The proposed topology employs asymmetrical auxiliary circuits that consist of only a few passive components. However, the advantage of the proposed topology is significant: it achieves soft switching independent of line and load conditions. Detailed steady state and dynamic analyses are performed to understand the operating principle of the proposed topology and its performance. A dc blocking capacitor is essential to prevent the current sense transformer from saturation, and the study of this thesis shows that contrary to the conventional pulse width modulated full bridge converter, the peak current mode control can still be used along with the blocking capacitor in a phase shift full bridge converter. Design procedure for industrial application is presented. Experimental and simulation results of a prototype 500 W 350-400 Vdc to 55 Vdc converter operating at 100 kHz verify the analysis and design, and show an overall efficiency of greater than 97% at full load.