DC/DC converter for high input voltage: four switches with peak voltage of Vin/2, capacitive turn-off snubbing and zero-voltage turn-on

A new four-switch full-bridge DC/DC converter topology is especially well-suited for power converters operating from high input voltage: it imposes only half of the input voltage across each of the four switches. The two legs of a full-bridge converter are connected in series with each other, across the DC input source, instead of the usual topology in which each leg is connected across the DC source. The topology reduces turn-off switching losses by providing capacitive snubbing of the turn-off voltage transient, and eliminates capacitor-discharge turn-on losses by providing zero-voltage turn-on. (Switching losses are especially important in converters operating at high input voltage because turn-on losses are proportional to the square of the input voltage, and turn-off losses are proportional to the input voltage.) The topology is suitable for resonant and nonresonant converters. It adds one bypass capacitor and one commutating inductor to the minimum-topology full-bridge converter (that inductor is already present in many converters, to provide zero-voltage turn-on, or is associated with one or two capacitors to provide resonant operation), and contains a capacitor in series with the output transformer (that capacitor is already present in resonant power converters). The paper gives a theoretical analysis, and experimental data on a 1.5 kW example that was built and tested: 600 Vdc input, 60 V output at up to 25 A, and 50 kHz switching frequency. The performance agreed well with the predictions. The measured efficiency was 93.6% at full load, and was a maximum of 95.15% at 44.8% load