Study of Multiple Discontinuous Conduction Modes in SEPIC, Ćuk, and Zeta Converters

Abstract

In this paper, we studied the discontinuous conduction modes (DCMs) of modified versions of the SEPIC, Ćuk, and Zeta converters. The modified versions of these converters were obtained by adding an extra diode to the classical versions of these converters; thus, we obtained converters with multiple DCMs. In the case of the SEPIC and Ćuk converters, the additional diode was added in series with the inductor placed at the input port, thus resembling the connection of a four-diode bridge rectifier at the input (where these converters work as power factor correctors in AC/DC conversion). The 2 diodes of the modified versions of these converters define 4 possible conduction modes: 1 continuous conduction mode (CCM) and 3 DCMs. In this paper, the 4 conduction modes were exhaustively studied, calculating their voltage conversion ratios and the equations of the curves that define the borders between conduction modes in both open- and closed-loop operations. The conduction modes and the straight line that describes the converter operation are represented in a plane called the “k1k2 plane”. As in the case of other characteristics exhibited by the SEPIC, Ćuk, and Zeta converters, the conduction modes, the voltage conversion ratios in each conduction mode, and the boundaries between conduction modes, coincide for the three studied converters. Finally, all theoretical predictions resulting from the analysis were verified experimentally through a reconfigurable converter prototype, working as both modified SEPIC and modified Ćuk converters.