The best way to vary speed ac motor using PLC

I would like to ask a basic and simple question.
What can i use to vary a single-ph induction motor using PLC?
as far as i know is using VFD but quite expensive for a student like me. any other methods?just need some suggestion then i do the research myself on it.Please help me

Do a fourm search on single phase motor speed.

http://www.plctalk.net/qanda/search.php?searchid=837660

There is lots of informmation there - including discussion on the obstacles.