Series of two transistors forward ZVZCS converter with phase-shifted control for high input voltage

This paper presents a soft switching series two transistor forward converter (STTFC) in interleaving for high input voltage. Two identical two transistor forward converters are connected in series. The voltage stress of switching device and freewheeling diode is only half the input voltage. In control method, phase-shifted control is applied. All the switches are turned off with zero voltage switching (ZVS), leading switches are turned on with a zero voltage and and zero current switching (ZVZCS), lagging switches are turned on with zero voltage switching (ZCS). The advantages of the proposed topology is high reliability, high efficiency and low cost. The circuit prototype, theoretical analyses and the experimental results of the converter for input voltage 600-1200V, output 24 V/20 A, 20 kHz are presented. The principle balancing voltage automatically is discussed. The effect factors of the efficiency are analyzed. The design is suitable for high input voltage and high power application.