Power converters by their nature present hybrid behavior since they contains switched circuits. Such circuits can be described by a set of discrete states with associated continuous dynamics. In this paper a new hybrid model for a 3-cells power converter is proposed. This hybrid model incorporates both the continuous and discrete states allowing better understanding of the system operating modes and properties. Of particular interests the new concept of hybrid Z(TN) observability is used to deal with the observability of the capacitors voltages and a discussion on the achievable observation dynamics is given. A sliding mode observer strategy is derived to estimate the flying voltages of the converter. Furthermore, it is derived that under some specific control sequence, the observation errors are asymptotically stable. Finally, experimental results are presented in order to illustrate the performance of the proposed approach.