Here is a plan for a very small single to three phase converter. The plan was published in a 1966 Popular Mechanics issue, The author claims it works and there was a retail kit available to build it. I have never built it, so I can't vouch for it, but it is the easiest and smallest converter I have ever seen. I have many more modern plans that are larger and much more complicated constructions.
The author claims it will run 1 to 3 hp, 3 phase, Y wound motors, off single phase mains. This is one I would like to try some time, just to see if it works.