  The $U\rightarrow +\infty$ one-dimensional Hubbard model in an electric field
has be exactly solved, with an emphasis on the charge current. It is found that
undamped Bloch oscillations extensively exist in the system. Such conclusion
has also been discussed for more general cases and we find that it is closely
related to the temporal periodicity of the model Hamiltonian in electric field,
rather than to the integrability of the model. As a comparison, we have also
studied a model of electrons with $\delta$-function interactions in continuous
space, which is closely related to the Hubbard model, but is non-integrable;
and we find that the charge current strangely shows a dissipationless behaior
which is comparable with the undamped Bloch oscillations.
