Average and Small-Signal Model of the Four-Switch Buck-Boost Converter under both Duty-Cycle and Phase-Shift Modulation

The four-switch buck-boost (FSBB) topology is often used in combination with other isolated converters to extend the voltage range capability of the overall structure. In such applications, the duty-cycles of the two legs of the FSBB are independently controlled, and a phase-shift is introduced in order to shape the inductor current ripple and thus achieve zero voltage switching. This paper proposes a non-linear average model, and the corresponding linearized small-signal model, for the FSBB operated in the described way. The derived average and small-signal models are shown to be in excellent agreement with simulation and are also validated by measurements on an experimental prototype.