Modeling of a SEPIC Converter Operating in Discontinuous Conduction Mode

A SEPIC (Single-Ended Primary Inductor Converter) DC-DC converter is capable of operating in either step-up or step-down mode and widely used in battery-operated equipment. There are two possible modes of operation in the SEPIC converter: Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). This paper presents modeling of a SEPIC converter operating in DCM using the State-Space Averaging (SSA) technique. The modeling leads to a small-signal linear model of the converter, from which the transfer functions used for feedback control design can be determined. It is found that the derived model is a reduced-order model, which can accurately predict the converter's characteristics up to one-tenth of the switching frequency.