Raj, Thanks for reply. I will elaborate my situation little more here:
My hardware is already fixed, I am only doing the firmware part.
It uses a PIC16F72 running at 20MHz(Instruction cycle = 200nsec at 1/4th fosc).
Sinewave output is fed back to ADC input of 16F72, via an OP-AMP so as to generate a 2.5V centered sine wave.
PWM output is 6.4KHz, thus period is 156usec per pulse. There are total 64 values per half cycle. I am using two timers to generate the PWM - Timer 0 running at 156usec continuously while Timer 1 running at ON period as per sine table.
My algorithm is:
At the first occurrence of timer 0 interrupt, start ADC acquisition.
On next timer 0 interrupt, the acquisition is completed, so start conversion and enable ADC interrupt.
When ADC interrupt occurs, read ADC value, add it to Sum (Variable initialized to zero).
This repeats for one half cycle and I get 32 values summed.
At the crossover point i.e. when the next cycle begins, I calculate average of all these summed values and using this value as the feedback representing the sine wave amplitude. The sum is then initialized to zero again.
If this feedback is lesser than THRESHOLD_LOW, then multiplier is increased and if this feedback is higher than THRESHOLD_HIGH, then multiplier is decreased.

You can say it is a layman's method for closed loop control and I am myself not satisfied with the results yet.

I would like to go for waveform adjustment but not having any idea how to do that. For e.g. I can store these 32 readings in an array and then compare it with a stored array of 32 values representing ideal sinewave. If I find that some particular value is higher than the stored value then that particular pulse width will be reduced. Is it the way to do waveform adjustment? It does not involve multiplier adjustment? Moreover, when the waveform gets clipped, if we increase the pulse width, the waveform will get more clipped. How to achieve control over that then?

Pleas advise me.


Mahmood, Thanks for your reply. Rectification doesn't produce linearly varying values for clipped sinewave. Will use of op-amp help here?

This particular inverter uses PIC16F72 with AC feedback. It is a 800VA domestic use inverter.