A Zero-Current-Switched PWM Full Bridge DC-DC Converter

In this paper a full bridge isolated DC-DC converter is proposed where the active switches are zero-current-switched (ZCS) for the entire range of operation. The proposed converter is targeted for high voltage, high power applications where input side bridge employs insulated gate bipolar field effect transistors (IGBT) and zero voltage turn OFF (ZVS) cannot be fully realised due to the tail current of the IGBT. The input side bridge has three half-bridge legs followed by two high frequency transformers. The Net output of the transformers is fed to a diode bridge feeding a resistive load through a LC filter. In contrast to the conventional phase shifted full bridge converter (PSFB), during the zero state (when there is no active power transfer from input to output), current does not circulate in the input bridge as well as in the transformers. Also the converter has low duty cycle loss. Thus the converter is suitable for the applications with wide output voltage variation as well. The proposed circuit also ensures soft commutation of the diode bridge rectifier. The converter operation principle is discussed. A 1.5 kW prototype is built and tested. Key experimental results are presented to verify the operation.