  We analyse dark energy models where self-interacting three-forms or phantom
fields drive the accelerated expansion of the Universe. The dynamics of such
models is often studied by rewriting the cosmological field equations in the
form of a system of autonomous differential equations, or simply a dynamical
system. Properties of these systems are usually studied via linear stability
theory. In situations where this method fails, for instance due to the presence
of zero eigenvalues in the Jacobian, centre manifold theory can be applied. We
present a concise introduction and show explicitly how to use this theory in
two concrete examples.
