\documentclass{article}
\usepackage[NewCommands]{ragged2e}
\begin{document}
{\centering
1abc
}
{
\CenteringLeftskip 0pt plus .5\hsize
\CenteringRightskip 0pt plus .5\hsize
\centering
2abc
}
{
\hbadness10000\emergencystretch\hsize
\centering
3abc
}
\end{document}