Variable Speed AC Motor

Hello Am wondering if someone has had experience with or has built a Variable Freq. Drive for a brushless AC motor , I have a 1/12 HP motor for a welder fan , this is a sealed brushless motor that I would like to run at a slower speed , part of the time it would be at the full 1550 RPM and I would like to run it about half that speed , motor normally runs on 230 volt , have had it running for about an hour at 115 volt , does get a little warm , am not sure if it would last all day at that temp. , lowering voltage is a simple solution , not very efficient and breaks every rule , I just thought someone might have been down this road before and could give me a few words of wisdom , lots of [3] speed motors on the market , most of them have an open cage that lets all the dirt go inside , or go in the wrong direction , would really like to keep the motor I already have . Thanks Phil