Design and Control of Fault-Tolerant Nonisolated Multiphase Multilevel DC-DC Converters for Automotive Power Systems

In this paper, a bidirectional, nonisolated dc-dc converter with several interleaved phases of multilevel modules for dual low-voltage automotive power systems is presented. Instead of using a two-level stage with short-circuit protection elements, a three-level module in a multiphase structure is proposed to achieve improved fault-tolerance. The dimensioning of the required flying capacitor for multilevel dc-dc converters is described. Further, benefits such as ripple reduction, automatic fault current limitation, and enhanced efficiency are achieved. Moreover, the control strategy for normal operation including the stability of the flying capacitor voltage as well as reconfiguration after semiconductor open- and short-circuit failure for ongoing degraded operation are explained.