Operation of fault-tolerant non-isolated multiphase 3-level DC-DC converters for 48 V automotive power systems

The operation of a non-isolated, bidirectional DC-DC converter with several interleaving phases of 3-level flying capacitor modules for automotive power systems is analysed in theory and a 3-phase prototype implementation. Control techniques for equal phase current sharing and flying capacitor voltage balance are applied. The converter efficiency is compared to a status quo 2-level multiphase converter with protection switches. Moreover, the system behaviour in case of semiconductor switch failures is investigated. The 3-level modules are always superior to a 2-level structure and need only the relatively small flying capacitor as additional component.