Development of a Four-Switch Buck-Boost Converter: Operation Modes, Control and Experimental Results

This paper presents the development and practical implementation of a four-switch buck-boost converter for variable input voltage. The circuit operates in buck or boost mode when the input values are higher or lower than the output. For voltages near the required level, the traditional buck-boost mode is replaced by modes A and B consisting in the combination of some periods working in buck mode with others working in boost mode. The sequence and duty cycle assignment of these transition modes are defined according to an approach based on steady-state analysis and discrete-time models. The digital system is completed by the addition of a voltage control loop that regulates the output under possible perturbations. Experimental results show that the proposed modes A and B present less ripple and appreciable less losses than the buck-boost counterpart. Thus, the prototype achieves efficiencies above 95% for all the input range and nominal load.