Your descriptions above are slightly confusing..

If you want to make a controlled 3ph rectifier to drive a DC motor...then you would need a thyristor bridge and phase angle delay techniques to control it...

So it would be a relatively simple matter of detecting the zero crossing of each phase ,then applying a timer based delay to retard the firing of the thyristors.

I could be wrong ,but I dont think its possible to make a 3ph rectifier using 6 igbt's ?..

If your aim is to produce a controlled AC output using 6 igbt's ,a standard 8051 running a sinusoidal software PWM will not be easy.

The CAPCOM of the Infineon chips has a feature not usually found in PCA's ...It has the ability to count up and down (in effect your triangle wave)..
Combined with the ability to compare in either direction...This make it far simpler to produce a 3ph output with a low cpu load..

Motorola also produce the MC3PHAC , which may be an easier solution as it requires no programming on your part..


Is this an educational project?..

Rob