To use Subversion (SVN) under Windows on JetBrains PHPStorm 7, 8 and 9 you`ll need to install the Subversion Client  1.8.x from CollabNet first.
This can be found at www.collab.net/downloads/subversion

After installing the client, go to File –> Settings –> Version Control  –> Subversion
And set the path to C:\Program Files\CollabNet\Subversion Client\svn.exe   or whatever path you have installed the client in to.