Centered text, aligned left

You could use a tabular which aligns the text to the left and is itself centered in the text. This could look like this:

\documentclass{scrreprt}
\usepackage{lipsum}
\begin{document}
 \lipsum[1]
 \begin{center}
  \begin{tabular}{l}
    This is line 1 with some text. \\
    This is line 2 with a slightly different text \\
    Line 3 is completely different and also a bit longer. \\
  \end{tabular}
 \end{center}
\end{document}

The output looks like this: