Use any DC-DC controller (TL494, SG3524 etc) to convert 12V to 300V and any controller with 4 hardware PWM channels + 4xIGBT bridge to create sine wave by modulating PWM using sine table and DDS principle.
lots and lots of reading, and training.
find some good books on theory there are some on the net free and for sale
Find someone who is good at electronics and would be kind enough to be your mentor as you learn and experiment