I. Introduction
The main advantage of three-level converter (TLC) is that the voltage stress on switches is only the half of the input voltage, so TLC is very suited for high voltage and high power DC-to-DC conversion [1]. [2] analyzed the derivation of TLC, and extended the derivation to all the dc-dc converters, and proposed a family of TLCs, including Buck, Boost, Buck-Boost, Cuk, Sepic, Zeta, Forward, Flyback, Push-Pull (PP), Half-Bridge (HB), Hybird Full-Bridge (H-FB) and Full-Bridge (FB) TLCs. [3] introduced the concept of blocking capacitor and modified the six non-isolated TLCs to make the output share ground with the input, among which the Buck TLC and Boost TLC are the same as the converters proposed in [4]. The blocking capacitor is essentially the same as the flying capacitor popularly called in three-level and multi-level converters. So hereinafter we rename the blocking capacitor as flying capacitor.