Boundary control of buck-boost converters: normalized trajectories and the Natural Switching Surface

This paper derives the natural trajectories for buck-boost converters and defines the Natural Switching Surface (NSS) control law to obtain enhanced transient responses. The study performed in the normalized geometrical domain provides understanding of the transient behavior of the converter and generality to the equations. The analytical framework proves that the converter can be operated at the physical limits. As a result, an excellent dynamic response during start-up and large load disturbances is achieved using the resulting Switching Surface (SS), accomplishing steady state in only one switching action. The analysis presented in this paper completes the theory of control using natural trajectories for basic topologies - buck and boost, with the addition of buck-boost. A design procedure, along with experimental results are presented to confirm the benefits of the normalization method and illustrate the qualities of the Natural Switching Surface.