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Abstract: this paper deals with the modeling of switching systems (a class of hybrid dynamical systems) using the bond graph formalism. The switching components are modeled using an ideal representation so that a variable topology system is obtained. If the system has n switches only a few mode among the 2 n are valid (the Kirchhoff's law must be respected). The purpose of this article is to establish some properties allowing to determine the sequence of the modes using some results concerning the determination of valid modes and the notion of reference mode. As a consequence the working of a static converter can be deduced from structural properties of the system without to adopt the classical scheme that consists in making assumptions about the state of the switches. Two examples illustrate those ideas at the end of the paper