The architecture of a back-to-back converter, needed to feed the rotor windings
of a 3-phase doubly-fed induction machine and such that power can flow both ways,
is described, from both the modelling and experimental viewpoints. In particular,
a PCHS model using selected GSSA variables is described in detail. Some new and
improved results concerning the detailed PCHS structure of a GSSA expansion of
a PCHS are also presented.