How do you design a three phase to single phase transformer 415v input 220v output 15kva?

might be interested in having a look at this:

Single-phase power through three-phase self-excited induction generator utilizing renewable energy resources

by Goel, SK (Goel, Sandeep Kumar); Srivastava, A (Srivastava, Ajay)

search for it online

Regards,

Bill