Small signal modelling of open-loop SEPIC converters

This study presents the application of a signal flow graph and the Mason´s gain formula for deriving small signal models of open-loop single ended primary inductance converter (SEPIC) converters. The control to output and the input to output transfer functions are derived. Conventional modelling methods using the averaging and small signal linearisation techniques are powerful for basic converters like buck and boost. However, for high-order converters like SEPIC, solving of high-order symbolic equations becomes complex and difficult. In this study, the application of the signal flow graph and the Mason´s gain formula help the manipulation of equations. Thus, derivation of small signal models can be easily carried out in detail. Theoretical and measured results are shown to verify the accuracy of the derived small signal models.