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.

A Systematic Method for Studying the Use of DC/DC Converters With Three Discontinuous Conduction Modes as Automatic PFCs

“…Two different trajectories have been drawn in this figure: α = 1 and α = 0.3. The expressions that define the DC conversion ratios for each conduction mode (expressions in the forms ( 18) and ( 19)), are as follows [13]:…”

“…1. • Converters with two diodes that remain in inductive branches when the transistor is OFF (and therefore converters with three DCMs), working as conventional DC/DC converters [12] and [13] (i.e., as in the first case, constant output voltage, limited input voltage variation, and fast duty cycle variation characterize their operation).…”

“…Let us consider conventional DC/DC converters, but now with two diodes and two inductors (L 1 and L 2 ). If the two diodes remain in two inductive branches (made up of inductances L 1 and L 2 or a combination of the two) when its transistor is in OFF state, then the converter will have four conduction modes, one CCM and three DCMs [12], [13], [15], [16]. An example of the current passing through the converter diodes is shown in Fig.…”

“…which is the boundary DCM1-DCM3, valid for when 0 < k 1 < k 1 Pc . As demonstrated in [13], equations ( 42)-( 51) are also valid for a Ćuk converter with an additional diode at its input port.…”

“…That paper examined the use of a Versatile Buck-Boost converter. This same method was applied in [13] to address the case of SEPIC and Ćuk converters with an additional diode in series with their input inductors. In all of these cases (Versatile Buck-Boost and the modified versions of the SEPIC and Ćuk converters) three DCMs are possible, and their main characteristics were correctly identified and verified in both papers.…”