  We study partial supersymmetry breaking from ${\cal N}=2$ to ${\cal N}=1$ by
adding non-linear terms to the ${\cal N}=2$ supersymmetry transformations. By
exploiting the necessary existence of a deformed supersymmetry algebra for
partial breaking to occur, we systematically use ${\cal N}=2$ projective
superspace with central charges to provide a streamlined setup. For deformed
${\cal O}(2)$ and ${\cal O}(4)$ hypermultiplets, besides reproducing known
results, we describe new models exhibiting partial supersymmetry breaking with
and without higher-derivative interactions.
