3 phase Electronic soft start

I'm trying to design a 3 phase soft start for an induction motor using 30Vac. I've used a TCA 785 chip from siemens without luck as the chip seems to be unstable,it fires the triac at one time but the stops the next. Can anyone help me in designing one including any suggestions on chips and circuits if possible.

put some NTC in the lines is one cheap,easy option (to a certain power levels)

Please post the schematic.