Soft switching hybrid converter with low circulating current

In this paper, a new hybrid dc-dc converter with low circulating current within the freewheeling interval, wide range of zero voltage switching (ZVS) and reduced output inductors is presented. The proposed hybrid circuit includes two three-level pulse-width modulation (PMW) converters and a series resonant converter with shard power switches in lagging leg. Series resonant converter is operated at fixed switching frequency (close to series resonant frequency) to extend the ZVS range of power switches at lagging leg. The output of series resonant converter is connected to the secondary sides of three-level converters to produce a positive rectified voltage instead of zero voltage. Hence, the output inductance can be reduced. The reflected positive voltage is used to decrease the circulating current to zero during the freewheeling interval. Therefore, the circulating current losses in three-level converters and series resonant converter are all improved. Finally, experiments are presented for a 1.44kW prototype circuit converting 800V input to an output voltage 24V/60A.