Clamped Topology Morphing of the Isolated Full-Bridge Converter for Reduced Rectifier Semiconductor Blocking Voltages and Transformer Volume

Inhalt:
To operate the isolated full-bridge converter at high input voltages, the operation can be extended from the conventional full-bridge operation to the half-bridge mode where one switch is continuously turned on and the other switch of the same bridge leg is turned off. To switch from one operating mode to the other, the on-the-fly morphing modulation is employed. This paper shows that the conventional morphing modulation has two major flaws - critically high blocking voltages of the rectifier stage semiconductors and an increased transformer flux. To solve this issue, a transformer clamping method is proposed along with a modified modulation. The concept is validated both by simulations and experiments. Enabled by the proposed modulation, the transformer can be build up with a smaller cross section and rectifier elements of reduced blocking voltages can be employed.