The more common technique is one used by variable speed drives and that is rectifying the mains into a capacitor and using pwm to drive IGBTs or MOSFETs to regenerate the ac waveform with the required frequency and amplitude. Not something that is particularly easy. I would suggest trying the Internation Rectifier site for some app notes.
as I suggested, this is the technique used in AC motor variable speed control i. e. the "inverter"

Erik