An Energy-Based Model of Four-Switch Buck-Boost Converters

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 typically used 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 operating in the described way. Notably, the proposed approach is based on the modeling of the inductor energy, which allows the correct description of the dynamics related to the phase-shift, in addition to those related to the duty-cycles. The derived models are shown to be in excellent agreement with simulation results and are also validated by measurements on an experimental prototype.