Depressing The Voltage Oscillation Across The Rectifier Diodes Of Full-Bridge Converter With Current-Doubler-Rectifier

Phase-shifted (PS) full-bridge (FB) converters can realize zero-voltage-switching (ZVS) for the power switches with the use of the leakage inductor of the power transformer and the output capacitors of the power switches, and they have been widely used in medium-to-high power conversion applications. There are different output rectifier topologies for the FB converters. Compared with the full-wave rectifier, the current-doubler rectifier (CDR) has a simple configuration for only one secondary winding. Meanwhile, the output filter inductor current is only half of the load current, and this is beneficial for high output current applications. This thesis focuses on depressing the voltage oscillations across the secondary rectifier diodes of the CDR FB converters.Two clamping diodes can be introduced to the primary side of the transformer to eliminate the voltage oscillation caused by the reverse recovery of the diodes. The principle of operation of the CDR FB converter under continuous current mode (CCM) and discontinuous current mode (DCM) is analyzed in details, respectively. The comparison between the FB converters with CDR and full-wave rectifier under DCM is given particularly when the clamping diodes are introduced. Under DCM, the clamping diode current in the CDR FB converter decays faster than that in the full-wave rectifier FB converter, which leads to shorter conduction time and lower average current, and thus, lower conduction losse of the clamping diodes. Morever, the clamping diodes can achieve zero-current turn-off, and the reliability of the converter can be improved.In order to reset the clamping diode current, this thesis proposes a CDR FB converter with an auxiliary transformer. The operation principle of the proposed converter at CCM and DCM is analyzed in details. Particularly, the comparison of with and without the auxiliary transformer under DCM has been given in details. With the auxiliary transformer, the current of the clamping diodes declines faster under the light load condition, thus the clamping diodes are soft turn-off, and the conduction loss is thus reduced.In order to verify the theoretical analysis, a 600 W prototype is built in the laboratory. The design procedure of the proposed converter is given, and the experimental results are provided.