  In systems with time-reversal symmetry, the orbital magnetization is zero in
equilibrium. Recently, it has been proposed that the orbital magnetization can
be induced by an electric current in a helical crystal structure in the same
manner as that in a classical solenoid. In this paper, we extend this theory
and study the current-induced orbital magnetization in a broader class of
systems without inversion symmetry. First, we consider polar metals which have
no inversion symmetry. We find that the current-induced orbital magnetization
appears in a direction perpendicular to the electric current even without
spin-orbit coupling. Using the perturbation method, we physically clarify how
the current-induced orbital magnetization appears in polar metals. As an
example, we calculate the current-induced orbital magnetization in SnP, and
find that it might be sufficiently large for measurement. Next, we consider a
two-dimensional system without inversion symmetry. We establish a method to
calculate the current-induced orbital magnetization in the in-plane direction
by using real-space coordinates in the thickness direction. By applying this
theory to surfaces and interfaces of insulators, we find that an electric
current along surfaces and interfaces induces an orbital magnetization
perpendicular to the electric current.
