cwd is the Net::FTP method name; cd is the standard FTP and shell command for changing directories. You may be confusing the two. The question is what your FTP server does when you call Net::FTP's cwd method.

I built a directory/file browser package on top of FTP and have run it across a variety of FTP servers. I have never found any that don't support Net::FTP's cwd method. I have found that I need to configure whether the ls or dir method is used to get long directory listings.