  A critical challenge in power conversion in electric vehicles is the
efficient use of DC-DC buck converters that need to provide 12-V supply for
load systems from 400/800-V batteries. This paper presents a literature review
on the development of DC-DC buck converters. Moreover, one novel four-phase
interleaved step-down topology is selected for simulation and hardware
experiments. Based on the four-phase interleaved structure, an extended-phase
topology is proposed, which has a higher voltage conversion ratio. Control
techniques are also applied to it. Theoretical analyses and simulation results
are provided to verify the improved converter. A 400V-to-12V and 150W output
power hardware prototype is implemented to verify its performance
