Instability of dc-dc converters at the boundary between CCM and discontinuous capacitor voltage mode [articol]

Abstract

In this paper, the operating mode between Continuous Conduction Mode (CCM) and Discontinuous Capacitor Voltage Mode (DCVM) of dc-dc converters is investigated. A large-signal model for the switching network is obtained. The small-signal averaged model is derived, and it is used to obtain analytical expressions for the small-signal transfer functions, for the ĆUK, SEPIC and ZETA converters. It is shown that the transfer functions exhibit at least one right half-plane (RHP) pole. This pole cannot be eliminated by varying the circuit parameters. From this it is concluded that the operating mode between CCM and DCVM is unstable and unusable.