Maybe its a crazy idea (the simple option)
The simple option is ,can't you do it like with big transformers .
Small (high powered) resistor in serie that you will bridge after the initial inrush .
Second option a bit less simple but a lot more sophisticated .
That option is called a ac-ac chopper .www.stmicroelectronics.com/stonline/books/pdf/docs/12105.pdf
You can simplify this schema quite a bit
(dispose of the switcher) use conventional powersupply .
Use a opto-gatedriver for the highside .
Leaves a bunch of fast diodes ,igbt's .
Ofcourse you will have to make something up with zerocrosssing detection to make it run nice in 3 phase .
Those mcu's aint that expensive just use 1 for every faseand have it triggered by zerocrossing
Goodluck and be carefull