  In this paper, we investigate the dynamical formation and evolution of 2 +
1-dimensional charged black holes. We numerically study dynamical collapses of
charged matter fields in an anti de Sitter background and note the formation of
black holes using the double-null formalism. Moreover, we include re-normalized
energy-momentum tensors assuming the S-wave approximation to determine
thermodynamical back-reactions to the internal structures. If there is no
semi-classical effects, the amount of charge determines the causal structures.
If the charge is sufficiently small, the causal structure has a space-like
singularity. However, as the charge increases, an inner Cauchy horizon appears.
If we have sufficient charge, we see a space-like outer horizon and a time-like
inner horizon, and if we give excessive charge, black hole horizons disappear.
We have some circumstantial evidences that weak cosmic censorship is still
satisfied, even for such excessive charge cases. Also, we confirm that there is
mass inflation along the inner horizon, although the properties are quite
different from those of four-dimensional cases. Semi-classical back-reactions
will not affect the outer horizon, but they will affect the inner horizon. Near
the center, there is a place where negative energy is concentrated. Thus,
charged black holes in three dimensions have two types of curvature
singularities in general: via mass inflation and via a concentration of
negative energy. Finally, we classify possible causal structures.
